Why Isn’t It “Platinium”?

The majority of chemical elements have names ending in “-ium”. In British English, we also have “aluminium” as opposed to the American “aluminum”, but we also have “tantalum” and “platinum”, so oddly the usual “-ium” ending has a couple of exceptions, as is common with spelling, grammar and word formations. The periodic table generally shows the order of discovery in how the names are formed. The older elements tend to have less regularly-formed names such as “phosphorus” and “antimony”, then after a certain point several half-hearted attempts to regularise them (e.g. “hydrogen”, “nitrogen”, “oxygen”) ensued, but it’s all rather haphazard.

The individual groups sometimes have some kind of order imposed on them. All the halogens, even the transuranic tennessine, end in “-ine” and no other element does. All the noble gases except helium end in “-on”, but this is rather spoilt by the names “carbon” and “silicon”. In a way, it makes sense that helium should have a different ending because it isn’t a typical noble gas, having only two electrons in its sole orbital as opposed to eight, as the others have. Incidentally, the noble gases are easy to contemplate in physical terms because they all consist straightforwardly of single atoms with regularly increasing weight. Oganesson, which is a transuranic noble “gas”, has a melting point of 52°C, but it can’t really exist in bulk. It would, I’m guessing, be a non-metal and therefore an oddity being so heavy and yet not a metal.

There have been two systems of nomenclature for elements which are either not yet discovered or unfamiliar. One of them imposed Sanskrit numeral prefixes, though only “eka-” and “dvi-“, i.e. one and two. This was where there were gaps in the periodic table, so for example gallium was originally called “ekaäluminium”, or perhaps “ekaäluminum” because the predicted metal hadn’t been discovered yet. This system is obsolete as all the holes in this portion of the table have now been filled. There is also the issue of what happens towards the end of the periodic table, where new elements have been discovered on a semi-regular basis. This system uses Greek and Latin numerals as prefixes for “-ium”, as in “ununoctium” for oganesson, but the numbers are chosen so as not to produce ambiguous abbreviations. They consist of the atomic number in decimal and yield three-letter symbols rather than the more usual two- or one-letter ones, which makes sense because these elements don’t meaningfully participate in chemistry owing to their instability. It would of course be possible to name all the elements in this way, producing a word like “nulnulhexium”, or possibly just “hexium”, for carbon, and “septoctium” for platinum, but this is unnecessary. One thing which somewhat bothers me about these names is that they use the decimal base rather than something which seems more fundamental such as hexadecimal or binary, or perhaps a base which matches the length of the sequences in the periodic table itself, which would give the elements systematic names matching their groups. They’re not as neat as they might villa .

The ending “-um” is clearly straightforwardly from the Latin neuter second declension, and there are also the “-on” endings from the same Greek declension. It seems to have connotations of “inanimate thing” in this context, so for example gallium is “Gaul thing”, i.e. the thing named after the country of France. There doesn’t seem to have been the kind of drive to neutrality which exists in astronomical naming. For instance, the constellation Scutum used to be called Scutum Sobieskii, but the second part was dropped, I presume because it refers to Poland, but polonium is still called that. This location naming business has led to the Swedish village of Ytterby, population 3 000, giving its name to no fewer than four elements (ytterbium, terbium, yttrium and erbium) due to the discovery of a dark, heavy rock in the area. Other elements are named after Stockholm and Scandinavia in their own way (holmium and thulium) for the same reason, and there’s also scandium. This seems disproportionate.

You will be aware though that the majority of elements ending in “-um” have an I before that ending, so the question arises of why there are exceptions. Aluminium is the oddest one of these because it varies according to American and British usage. The metal was discovered by Humphry Davy by electrolysis from alumina, which is aluminium oxide, and he originally called it “alumium”. In 1812, he changed the name to “aluminum” but this was difficult to maintain because of its lack of conformity. It got adopted by the general public in the US but not by American chemists, whilst in the Commonwealth it was uniformly “aluminium”. Canada, though, uses “aluminum”, as it’s generally more American than the rest of the Commonwealth, and also more American than Ireland come to think of it. The International Union of Pure and Applied Chemistry (IUPAC) recommends “aluminium”.

Even so, there are four other elements like this, namely molybdenum, lanthanum, tantalum and platinum, and these always use that form. All of the other “-iums” always use that form too. Platinum was the first element to be given a name ending in “-um” officially after discovery, so it could be that the convention of inserting an I was yet to be established. All of the elements discovered prior to it ending in “-um” in Latin have no I: plumbum, aurum, argentum, ferrum, hydrargyrum. However, “zinc” is cadmiæ. Hence there are two other questions. Firstly, why did they start sticking an I in in the first place? Following that, why are there later discoveries without an I? Molybdenum was discovered before they started putting it in, and the first one with an I is tellurium. Tantalum was named long after it was discovered and lanthanum was discovered quite late. It’s distinctive in that like actinium it’s the name of a whole series of similar elements. Tantalum is presumably called that because Tantalus wasn’t called “Tantalius”.

Hence it does make sense, historically, that platinum has no I. Platinum has strong symbolic value compared to the other platinum metals, which are relatively obscure, being used, of course, for the platinum anniversaries and the jubilee, the only one in the history of any of the home nations, so it’s appropriately rare. It also turns up in platinum discs and platinum blond hair. There is, however, no “Platinum Age” or a platinum medal. The latter is easy to understand, since it would involve disrupting an established system and render previous gold medals invalid, and the older version of the age system was thought up before platinum was known in the Old World. It was, however, known in the New, being found in river deposits in South America before the Christian Era. It’s one of the densest and least reactive metals, has a very high melting point and is very hard. In spite of all these qualities, pre-Columbian artifacts made of platinum do exist, such as a mask and jewellery, occurring in present day Columbia and Ecuador.

Platinum is actually the most widespread platinum metal. Osmium and iridium, the heaviest elements of all, are not widely found on the surfaces of planets because they sink to the centre during their worlds’ molten phases. However, being an even-numbered element, platinum is more abundant than some of the others by virtue of that alone. Palladium is considerably rarer and osmium and iridium are mainly associated with their density rather than their use as precious metals. Osmium is the rarest precious metal of all, and also the densest, and is used in alloys to make pen nibs and in electron microscopy. It slowly oxidises in air and the fumes it gives off can cause blindness and lung damage. Iridium is well-known as the sign that non-avian dinosaurs were wiped out by the Chicxulub Impactor, as small celestial objects do not exhibit the stratification of larger ones due to their low gravity and often low temperature. Ruthenium, rhodium and rhenium are also platinum metals. They’re all useful as catalysts, famously in the case of platinum itself. The anticancer drug cisplatin contains it, and works like most anticancer drugs by interfering with DNA replication.

It may be just me, but I consider platinum blond hair as gendered in this culture. I’ve never been a fan of fair hair, on me or others, in æsthetic terms, but the technique for producing the effect is academically interesting.

Of course, the reason I’ve chosen to blog about this today is the fact that it’s the Jubilee, but I wanted to do so in a way which didn’t partake of any controversy between royalist and republican sentiments, so here it is.

Two Flowerings And A Cousin

Here at chez zerothly, the mornings are currently filled with the bongs and bings of Duolingo as Sarada and I vainly and not so vainly, not respectively, attempt to learn two distantly-related languages. Sarada is having a lot more luck than I am, or rather, she’s making progress much more rapidly. I am plodding, and as I advance through the lessons the number of mistakes I make grows steadily. I feel in no way on top of my learning, and that’s unusual for language learning for me, although not in any way a surprise in this case. Sarada in the meantime has a degree in French and is learning a closely-related language which she’s already made progress in through evening classes. As far as I can tell, the sum total of her efforts with respect to learning this language right now consist of Duolingo. My efforts consist of listening to radio stations in my language and watching the TV news in it. There probably isn’t much difference in our degree of motivation, but whereas she’s not putting as much time into it as I am, she’s getting a lot further a lot faster.

Both languages are Western European Indo-European KENTUM languages. I’ve been into the classification of IE languages before on this blog, but to cut a long story short, here’s a quick summary. The Indo-European language family is the largest and best-researched language family and consists of languages originating in Eurasia from Ireland and Portugal through to Bangladesh, extending into the Arctic Circle and across Russia. Particularly in Europe, there are only a handful of indigenous tongues which are not members. The family consists of three divisions, one much smaller than the other two and completely extinct, namely the Anatolian languages which include Hittite and were so ancient they were often written in cuneiform. Of the other two, one is probably a more genuine division than the other: KENTUM and SATEM, based on their words for “hundred”, which reflect sound changes in the two main branches. Although KENTUM languages tend to be more western in origin than the SATEM ones, the easternmost subfamily of all, completely extinct now for over a millennium, is Tocharian and is KENTUM. The SATEM group is probably not closely bound and likely reflects the languages which simply didn’t descend from the one which underwent the KENTUM changes rather than having a common ancestor beyond Proto-IE itself

I’ve covered all of this before. Among the KENTUM languages, as I count them, and this is not actually the official way they’re counted nowadays but I do this based strictly on the word for “hundred” which may have been altered by other influences, the branches are Illyrian, Tocharian, Celtic, Germanic and Italic. The sole surviving Illyrian language is Albanian, but there are likely to have been many others spoken in the Balkans which were never written down and just died out. I don’t include Greek because its word for “hundred” isn’t like ours, and I seem to remember that linguists often group it and Armenian together. However, the Armenian word for “hundred” is “հարյուր”, and I think you’ll agree that doesn’t look much like ours, beautifully written though it be. I am, incidentally, aware of the peculiar history of Armenian but I don’t want to get too sidetracked.

I’ve taken old written examples of each branch of the KENTUM languages and compared the vocabulary. I found, perhaps surprisingly, that the two closest seemed to be Latin and Gothic. This is a little misleading as history is, literally in this case, written by the winners, and the Albanians, Tocharians and Celts definitely didn’t turn out to be the victors in the long run. The Tocharians were so long gone and utterly eradicated that nobody even remembered they’d existed and they were only unearthed because they lived in a desert area of Chinese Turkestan where their documents were preserved by the conditions. The Albanians are the sole survivors who seem to have clung on because of living in an isolated mountain kingdom which nobody wanted and was in any case pretty inaccessible. As for the Celts, well . . .

On the SATEM side of things, Baltic and Slavic are evidently rather close to each other, and also influenced Germanic because the people speaking these languages didn’t have much respect for what philologists were going to do in fifteen centuries’ time, and therefore didn’t realise they weren’t supposed to speak to their KENTUM neighbours. In the KENTUM case, two subgroups are particularly close to each other, or rather, they’re closer than the others are, and also closer to each other than they are to the others. These are Italic and Celtic. In a late nineteenth century edition of Cassell’s Etymological Dictionary, a book I studied very closely as a child before I got a copy of Skeat as an Xmas present, Italo-Celtic was considered a single branch on the family tree rather than two.

Both the languages Sarada and I are currently learning, or in my case trying to learn rather unsuccessfully, are Italo-Celtic. Sarada is picking up Italian quickly and I am slogging away unfruitfully at that nasty grandparent language known as Gàidhlig. Sarada has on a number of occasions asked me why I’m bothering, considering it’s such a huge effort and such a minor language, to which my answer is that it’s an endangered language and part of my heritage. I’ve been into this before on this blog. I’m not going to pretend it’s easy, wonderful, beautiful or anything else, but the fact is that it’s on its last legs and deserves to be preserved. To compare, there are more than three dozen native American languages with more speakers than Gàidhlig and I’d never suggest that they should be allowed to die out, so here I am learning this language whose term for spider translates for some reason as “wild stag”, and in other circumstances I’d find that picturesque and charming but to be honest my immediate reaction is “Just why on Earth‽”. But this unlovely tongue is the one in which my surnames are, and what kind of rootless fool would I be if I couldn’t even pronounce my own name? So I’m stuck with it, and as you’ll know if you’ve been reading this blog, I consider myself obliged to learn the sodding thing. This is in no way a slight on the Gaels, which would be weird and self-hating to some extent anyway, though I consider myself a White Northwestern Eurasian above everything else (or a NW European if you want to be parochial about it). To be fair, I’m not a huge fan of English either due to things like its weird vowels and diphthongs, overuse of the word “do” and only having one word for “you”, but I honestly can’t say I actually prefer Gàidhlig as a language.

There’s considerable doubt about the validity of Celtic as an identity, but whatever is true, there are a maximum a few thousand speakers of each surviving spoken Celtic language, which are divided into two halves, P-Celtic and Q-Celtic according to how they treated proto-IE “KW”. P-Celtic survivors comprise Welsh, Cornish and Breton, plus a few words adopted into a now-extinct Siouan language called Mandan. The Q-Celtic languages are Gàidhlig, Irish and Manx, which form a linguistic continuum interrupted by the ingress of Scots and English into the southwestern part of what became Scotland, although a P-Celtic language was also spoken there. It must also be mentioned that all surviving Celtic languages have mysterious similarities to Afro-Asiatic languages such as Arabic and Hebrew which have never been explained, and again I’ve been into this before.

All that said, this isn’t what I’m going to focus on today. Rather, the activity of learning Gàidhlig just as Sarada is learning Italian has highlighted the possibility of Italo-Celtic as a division of the KENTUM branch of IE, and in fact if you go back far enough they’re remarkably similar, particularly if you take out the bizarre Semitic tendency in Celtic.

The Italic languages are peculiar in that they’ve flourished twice. They’re the only example I know of a language group which developed into a whole range of spoken languages, all but one of which died out, only for that sole survivor to become another whole range. That was of course Latin, and its descendants the Romance languages, including Italian itself and also Catalan, Provençal, Romanian, French, Castilian and various others. Traces of the older Italic languages still exist in Italian dialects but the only one to emerge and spread from the Italian peninsula was Latin itself. The others were Oscan, Umbrian, South Picene, Faliscan, and possibly Ligurian, Sicel, Nuragic, Raetic and Venetic. There were also other less-closely related languages spoken before the founding of Rome on the peninsula and associate islands, including the unclassified Etruscan, which was definitely not IE but whose actual allegiance can’t be traced definitively, and also Illyrian languages and Greek, as well as Punic, an Afro-Asiatic language spoken in North Afrika. The actual Italic speakers had migrated southward from the trans Alpine region, and this is where the Celtic connection becomes apparent.

The area north of the Alps was Celtic at the time, insofar as the Celts ever really existed in their own right, so either the speakers of the Proto-Italic language were in contact with the speakers of Proto-Celtic or they actually were the speakers of Proto-Celtic, id est they were actually the same language. I’m going to use Latin spelling here as I write the numbers from one to ten in Proto-Italic:

oinos, duo, tres, quettuor, quenque, sex, septem, octo, novem, decem.

Here’s the same in Celtic using the same spelling:

oinos, duau, tris, quetuares, quenque, suexs, sextam, oxtu, navam, decam.

I’d say these are close enough to be in the same language spoken in different accents. Proto-Celtic has a more archaic flavour to me, and the presence of the A’s in “navam” and “decam” give them a kind of Sanskrit flavour –  नव (nava) and दश (daśa) being the same words in that language. That doesn’t mean the rest of the two languages were as similar. For instance, even now some Q-Celtic uses a dual number – a form like the plural but for when there are two of something – but Italic has never had that, although it has traces such as “ambas/-os” in Castilian for “both”, and of course similar traces exist in English. That said, the languages are unusually similar.

You might be wondering how this can be reconstructed since this was all going on rather a long time ago. The answer is that Italic languages did in fact often have a written form, having alphabets derived from Greek, usually via Etruscan which was the high civilisation on the peninsula at the time. Each actually had a different script. Consequently it can be seen that there are a number of similar languages which have certain things in common and one-way processes can be identified. Italic is not puzzling in this respect. Celtic is somewhat more confusing, because the only surviving Celtic languages are the ones spoken in the British Isles and Breton, which is descended from a British Celtic language, and those only date from the first millennium CE in written form. There are older examples but these tend to be rather limited, consisting of short inscriptions. On the Iberian peninsula, five scripts existed which seem to have been derived directly from Phœnician. They tended to be syllabaries rather than alphabets, i.e. one character per syllable. Elsewhere, Celtic languages actually used Italic scripts, which considering they were in the same area is unsurprising but it illustrates the close contact between the two groups.

Turning to more general vocabulary, similarities are sometimes obscured by semantic drift, id est, changes in the meanings of words, as for example happened with our “silly”, “nice” and “gay”. For instance, the Proto-Celtic word for “snake” is “natrixs” but the Latin “natrix” means “water snake”, the Proto-Italic word being “anγwis”, which became the Latin “anguis”, which now means “slow worm”, and later the word for eel, “anguilla”. The vocabulary is in both cases also, unsurprisingly, both less “Latin” and less “Celtic” in character because it retains words from PIE which later disappeared and may also have picked up words from the Germanic tribes living nearby. Hence Latin “filia” for daughter is a replacement for a word closer to “daughter” which in Oscan, for example, is “futir”. Even so, various words are quite close or identical:

Proto-ItalicProto-CelticEnglish
tututhou
iseshe
quesquiswho
quidquiswhat
nenenot
aliosaliosother
anγustosangusnarrow
tenuistanauiosthin
virosvirosman
matermatirmother
paterφatirfather
piscisφescosfish
cocudog
palma (palm)φlamahand
auzisausosear
cordcridiomheart
canocanetising

There are many more examples, and this is not cherry-picked, although the words are from a core vocabulary which tends to change less than average. What I have done is ignore vowel length and adjusted both sets of spelling to a kind of classical Latin standard, which brings out how similar Proto-Celtic and Latin really are.

However, it’s uncontroversial that Proto-Celtic and Proto-Italic are related. This is already established. A proper study would compare it with the successful Germanic branch of the KENTUM group. Fortunately this can be done. Here are the numbers from one to ten in Proto-Germanic:

ainaz, twai, þriz, fedwor, fimf, sehs, sebum, ahtou, newun, tehun.

These are, as could be expected, somewhat similar to Italic and Celtic but don’t have the uncanny affinity shown between those two. As for the list above, the Proto-Germanic version looks like this:

þu, iz, hwaz, hwat, ne, allaz, anguz, þunnuz. weraz, moder, fader, fiskaz, hundaz, handaz, auso, herto, singwaną.

In this case, though, the words selected are synonyms whose alternate forms are not found, and as Germanic language users ourselves we can spot some of these, such as “allaz” and “anguz” for “other” and “narrow”, both of which already existed in Proto-Germanic in recognisable forms as “anþeraz” and “narwaz”. This doesn’t happen so much with Proto-Italic and Celtic. Germanic is distinctive in having a large number of words not closely connected to other IE words. Apparent examples here are “hand” and “sing”. But it could still be that Germanic is simply the outlier and Celtic and Italic developed along more typical lines. Except that this isn’t so.

As well as the similarities between words, the two languages also share other features not found in Germanic or any other IE languages. For instance, the superlative, expressed in English by “-est”, and similarly in, for example, Greek, is expressed in Italic and Celtic using an ending based on “-isṃmo-“, as in Italian “fortissimo” and Old Irish “sinem” – “oldest”. The subjunctive mood of the verb is descended from the proto-IE optative (“would that it. . .”) in both cases, which is highly unusual. The genitive uses an I in its ending in both cases too, and there are several other grammatical similarities. Again, these could be primitive features which survived in Italic, Celtic and nowhere else rather than direct connections between the two, but something like the adaptation of the optative to the subunctive isn’t an archaism or that mood would have been like that in Sanskrit, for example, and it isn’t.

The hypothesis became popular from the 1860s and was attacked successfully by the Harvard linguist Calvert Watkins in 1966, so it could be that my attachment to the idea is anachronistic. The problem is supposed to be that the features held in common each connect only one Italic and one Celtic language, and not the same pairs at any point. This is interesting for another reason. Celtic languages are fairly well-known for falling into two subgroups: P-Celtic and Q-Celtic. Hence the Welsh for “five” is “pump” but the Irish equivalent is “cúig”, and the Old Irish for “son” is MAQ, later “mac”, but the Welsh word is “mab”. For a while it was thought that this division merely occurred in the British Isles, but it turns out that continental Celtic languages were also divided in this way. Something similar happens in today’s Italic languages with, for example, the Romanian “patru” for Italian “quattro”, although this development occurred after Latin split up. It also, though, took place in the older Italic languages. Oscan and Umbrian use P where Latin and Faliscan use QU. Hence a weird division can be made among Italo-Celtic where Q languages include Italian, French, Manx and Irish, among others, whereas P languages include Breton, Welsh, Oscan and Umbrian, reflecting a tendency in the entire group for this to happen, as it has in Romanian for example. However, all these similarities don’t mean that Romanian and Welsh have a common ancestor in Oscan, and likewise some of the other tendencies might follow from a pre-existent state which trends in that direction. It’s similar to the phenomenon where both English and German started off with a long I pronounced “ee” and a long U pronounced “oo”, which however became “ai” and “au” independently: min – mine/mein; hus – house/Haus.

Nonetheless, I’m not writing this with the courage of my convictions and that long list of identical and very similar words is hard to discount. This part of western Eurasia can be simplified into a series of peninsulas. There’s Scandinavia in the north, the main part of Western to Central Europe further south and the separate peninsulas of Iberia, Italy and Greece stretching into the Med. The Greeks and Illyrians occupied the last and are not so relevant to the situation. The Germanic peoples originate in Scandinavia, a peninsula which provides an obvious stronger separation from the others, and the characteristics of our languages clearly show the influence of the Uralic languages, for instance in the absence of a separate inflected future tense. It makes sense that Germanic languages would be the outliers in this respect. Then, further south lie the Tumulus and then Urnfield Cultures of the Bronze Age, itself followed by the clearly Celtic Hallstatt Culture. The peoples of the first two of these came to radiate south into Iberia and Italy, but there was a period during which the Etruscans dominated in Italy and only later came to cohabit with the Italic-speaking peoples. These clearly came from the north, trans Alpine region, and the Alps clearly constitute a barrier between the Italics and the Celts. What seems to have happened, or might have anyway, is that the Italo-Celtic speaking people north of the Alps and also spreading into Iberia got separated from the Italic speakers of Italy, and the languages started to diverge, but it clearly makes complete sense that the Urnfield Culture, lasting from 1300 – 750 BCE, or put another way, the five and a half centuries before Romulus and Remus, spoke a group of dialects which were ancestral to both Irish and Portuguese, as it were, along with everything therebetwixt.

These two branches fared very differently. Italic languages kind of triumphed, although most of the first season became subsumed into Latin dialects, and in the form of Latin came to dominate first much of Europe and then the wider globe, such as South and Central America, the Philippines, the former French colonies, and indirectly in the form of English with its extensive French borrowings. Celtic had a very successful period during which it was spoken in the British Isles, Gaul, Iberia, Central Europe and Anatolia, but was then eclipsed by first Latin and then Germanic, leaving it spoken only in Brittany, Ireland and the west of Great Britain and nearby islands, although it did also reach Nova Scotia and Patagonia in the end, in small communities. The grammar of the two halves today shows almost nothing recognisable in common except for things like the occasional letter I in unexpected places in Q-Celtic, but the vocabulary is still faintly connected. This, however, is unclear because of the influence of the Church, leading to loanwords from Ecclesiastical Latin. The Celts are also outside the Empire. The languages were spoken and finally throve best where Latin was not spoken. Their distribution was complementary, and this complementarity followed class and ethnic divisions as well as geographic ones.

The Tumulus Culture is named after the practice of interring bodies in mounds of earth. This practice seems to have spread from the Kurgans of the area north of the Black Sea, named after similar structures, who are widely believed to be the original Proto-IE speakers, so it makes sense that these people would’ve been speaking the common ancestor of Celtic and Italic languages. Their successors, the Urnfield Culture, are named after their tradition of cremating their dead and burying them in urns in fields. If these people were indeed Celts, there may a direct line between this practice at the Cremation Act 1902, which legalised crematoria in Wales, England and Scotland. This act was passed after a famous test case where in 1884 an eccentric Welsh medical doctor, Dr William Price, cremated the body of his five-month old son on a funeral pyre and was tried for it. He was re-enacting a Druidic practice in doing so and was cremated himself a few years later in 1893. Hence our current practice of widespread cremation in Britain may be directly descended from the Urnfield Culture.

At this point, I should make it clear that I know practically nothing about archæology, so I’m venturing well beyond my comfort zone here and you should take what I’m saying with a larger than usual pinch of salt. I should also point out that I don’t in fact know why Celts are not considered an ethnicity beyond a very sketchy idea that they are generally just what the Romans and Greeks thought of as the “not-we’s”,which can’t be quite true or it wouldn’t explain Germans.

The idea that the Urnfield Culture is the original Celtic culture, or Italo-Celtic, is only one of several competing theories about the origin of the Celts. There are also “central” and “western” theories. The western theory is that Celtic languages began along the Atlantic coast and were used as an auxiliary language between traders. This then spread eastward. This is interesting because it seems to imply that the areas where Celtic languages are currently spoken were close to their original territory. The idea of Atlantic Europe is anthropological and in current terms includes Portugal, the British Isles, Northwestern France, the Low Countries, the hinterland of the German coast, Jutland and Norway. Interestingly from a British perspective, it has a Southwest-Northeast orientation like divisions on our own island. It used to be claimed that there was considerable genetic unity among the humans of this area, but in the case of the British Isles any sign of this is obscured by the presence of the R1b haplogroup, of which I have a subclade. This originated from the Yamnaya in the Copper Age, who were what used to be called the Aryans. That is, they were the original PIE speakers. They’re the fair-skinned lactose-tolerant people who tend to occupy Europe.

The “central” theory is that Proto-Celtic arose in Gaul and radiated thence, which makes it easier to account for the similarities in ancient Celtic languages over a large area. It also means that the Celts began close to Italy, which means the Italo-Celtic hypothesis can be maintained more easily.

One thing I haven’t done here is mention the ancient Celtic languages much. The oldest known written Celtic is Lepontic, found in Cisalpine Gaul from about two centuries after the foundation of Rome. There are also Celtiberian, Gaulish, British, Galatian (spoken in what became Turkey – it’s been disputed whether this is a truly Celtic language), Noric and Gallaic. Celtiberian in particular is of interest here as it’s a Q-Celtic language which seems to be ancestral to Irish and therefore also Manx and Gàidhlig, confirming the origin story of the Irish that they came from Spain. There’s actually a fair amount of continuous text available in Celtiberian because of the Botorrita Plaques, which are bilingual Latin and Celtiberian law codes dating from the fifth century Anno Urbis Conditæ. This is a fairly raw transliteration of one of the plaques (the language did not use the Latin alphabet):

trikantam : bergunetakam : togoitos-kue : sarnikio (:) kue : sua : kombalkez : nelitomnekue [: to-ver-daunei : litom : nekue : daunei : litom : nekue : masnai : dizaunei : litom : soz : auguaresta[lo] : damai : uta : oskues : stena : verzoniti : silabur : sleitom : konsklitom : gabizetikantom [:] sanklistara : otanaum : togoitei : eni : uta : oskuez : boustom-ve : korvinom-vemakasiam-ve : ailam-ve : ambidiseti : kamanom : usabituz : ozas : sues : sailo : kusta : bizetuz : iomasekati : [a]mbidingounei : stena : es : vertai : entara : tiris : matus : dinbituz : neito : trikantameni : oisatuz : iomui : listas : titas : zizonti : somui : iom : arznas : bionti : iom : kustaikosarznas : kuati : ias : ozias : vertatosue : temeiue : robiseti : saum : dekametinas : datuz : someieni touzei : iste : ankios : iste : esankios : uze : areitena : sarnikiei : akainakubosnebintor : togoitei : ios : vramtiom-ve : auzeti : aratim-ve : dekametam : datuz : iom : togoitos-kuesarnikio-kue : aiuizas : kombalkores : aleites : iste : ires : ruzimuz : Ablu : ubokum

Gallaic was spoken in Gallicia north of what is now Portugal. Only the occasional word has been recorded, but there are traces in placenames in Galicia and Portugal. This is somewhat complicated by the Celtic Britons who settled there after the fall of Rome, although their influence was minor. Galician and Portuguese both have some Celtic vocabulary, which is presumably from Gallaic.

Gaulish is well-attested. There are more than five gross Gaulish inscriptions and French has more Celtic loanwords than any other non-Celtic language has. It had essentially the same vowels as Classical Latin and the main difference in the consonants were the presence of velar fricatives “kh” and “gh”, and the affricate “ts”. It had seven cases, including the instrumental which had been lost in Italic but does exist in Germanic. Unlike the living Celtic languages or Latin, word order was subject-verb-object, like English. Gaulish is also quite close to British itself. The general impression given by Gaulish is that it’s basically Latin with different words and endings, it not having any of the peculiarities one tends to associate with the surviving Celtic languages such as the confounding periphrastic approach, unusual syntax and consonant mutation. All of that appeared later. Latin and Greek are only distantly related to each other but their general approach to grammar is very similar. The same approach is found in Gaulish.

There are said to be more living speakers of Celtic languages today than there were in Roman or pre-Roman times, so in a way this is their heyday, if that’s true. I think it probably helps to know that there’s a host of lurking cognates to Romance words in Gàidhlig even though the spelling is, though to some extent justified, really annoying. I’ve decided, sight unseen, to reproduce the above list of cognates in Gàidhlig once again, in the form of a table with Italian and English equivalents:

ItalianGàidhligEnglish
tuthuthou
lui, essoehe
chiwho
chewhat
nonchan eil(is) not
altroeileother
strettocaolnarrow
sottilecaolthin
uomofearman
madremàthairmother
padreathairfather
pesceiasgfish
canedog
manolàmhhand
orecchiocluaisear
cuorecridheheart
cantareseinnsing

This isn’t very promising, I have to say. I don’t know how Welsh fares here, although I get the impression it’s less peculiar than Gàidhlig. At least the spelling is clearer.

To conclude then, I wonder if the Romance languages had been as marginalised as the Celtic whether they would have changed in equally peculiar ways. I now realise how little I know about Celtic and the Celts, which may in fact not really have much in common, and I also don’t know why it’s often denied that there is even such a thing as Celtic identity, and what political significance that idea has. And finally, after looking at all this evidence and making a cursory attempt to test it rather than seeking confirmation bias, I definitely accept that Italo-Celtic is a valid grouping of IE languages, more closely bound than either is to Germanic or Illyrian, and that in the late Bronze Age they were a single language with dialects, in close proximity to other languages which were related but not mutually intelligible with it. And I don’t know why anyone would claim the contrary, but then I’m not a linguist.

«Je ressens la pluie d’une autre planète»

It’s a trite cliché that artists have to draw what they see, and with twentieth and twenty-first century art it seems to be false. Perhaps with Fauvism an artist might attempt to concentrate on how she might see a particular shade or hue and paint it as that colour throughout, or at least that’s the impression (!) I got. In fact it seems to be nothing like that, but it does force the viewer to see the geometrical components of a scene while retaining one’s emotional relationship therewith, or maybe the artist’s feelings. Cubism, a couple of years later, concentrates on geometry while removing emotion.

Right now I feel that my tour of the Solar System has to some extent placed me in the second category, but only somewhat. I expect, if someone had genuinely visited other worlds, if their experience of Earth on their return would be more emotionally charged. I’m sure they’d never be the same again.

There will be something like poetry. Where it starts is another matter.

In the park near us, there’s a small fountain in a pond. Its drops describe a series of parabolas. These parabolæ radiate from the central showerhed and rise maybe fifty centimetres from the water surface. They remind me, right now, of nothing so much as a volcanic eruption on Io. With its exceedingly tenuous atmosphere and gravity less than a fifth of Earth’s, the fountain of ejecta from Io’s volcanoes resembles the fountain in the park but is cyclopean in extent, being over 150 kilometres high. However, the same laws of physics govern the movement and form of the drops. This was the first alteration in perception I became aware of.

Swerving into herbalism territory, like most Western herbalists my stock-in-trade substantially comprises a series of bottles containing what probably look like thick brown liquids to most people. These are usually ethanol and water solutions containing dissolved active ingredients of the plants in question. I could go into more depth about the more subtle distinctions herbalists perceive in the appearance of these tinctures, but for quite a number of them the residue remaining if some is spilt and the solvents evaporate becomes a tarry, often reddish-brown substance which is often a mixture of tannins and other compounds. Tannins are generally linked rings of organic molecules with hydroxyl and oxygen groups. Bakelite is another example of a substance made of these phenolic rings, and the brown or black appearance of a caster, mains plug or saucepan handle is often due to this. And out there in the depths, or maybe heights, of the outer Solar System are countless worlds covered in tholins, which are in some ways similar to this residue, though not necessarily phenolic. The sticky, reddish-black tincture residue is substantially similar to the same stuff coating the surface of many TNOs.

Another parallel with herbalism occurs when certain worlds are cold enough to have frozen nitrogen on their surfaces, such as Pluto and Triton. This brings tholins into contact with the element, leading to the formation of organic compounds containing nitrogen. These are quite similar to alkaloids. Alkaloids are a group of compounds which each have some of the following characteristics: they all contain nitrogen and have a markèd physiological action, tend to have rings including a nitrogen atom, and originate from plants. There are exceptions to the last two and the function of the alkaloid for the plant in question isn’t clear – they may act as reserves of fixed nitrogen. Alkaloids include caffeine, nicotine, atropine and cocaine. There are research programs to find novel alkaloids in rainforest plants for medical use, a race against time thanks to deforestation. Well, heinous as that may be, it so happens that many outer system worlds are coated in nitrogenous organic compounds, and this is just me but I do wonder if there are many such compounds out there. Maybe there could be heroin mines on Charon. The Universe doesn’t care about that.

The way tholins spread across the surfaces of the likes of moons and asteroids is reminiscent of how mould, lichen or plants colonise a new habitat. They are, as I’ve said before, a fork organic chemistry can take when free from technological influence instead of coming alive. It’s literally true to say that there’s an organic quality to tholins. Alternatively, maybe the way tholins went on Earth involved a freak accident with them coming to life. Consequently, when I look at a road surface, wall, pavement or other stone-like artifact, I see a parallel to the surface of a distant planet, where reddish-brown tar is gradually being deposited, just as moss and lichen gradually creep across these fresh plains. The difference is that in spite of the amazingly gradual encroachment of lichen at about a millimetre a decade, it’s still thousands of times faster than the rate of tholin deposition.

I don’t know if you’ve ever been to Dungeness. This area of Kent, held constantly in place by shingle lorries shuttling to and fro 24/7, is an example of a rare type of habitat known as a shingle bank whose largest examples on Earth are it and Cape Canaveral. The delicacy of this landscape is such that walking across it will leave footprints visible decades later due to the slow-growing foliose lichen living there. It has to be said that putting one of NASA’s main launchpads there is rather questionable, and much of what I’ve been able to write about in this series is contingent on environmentally questionable launches from that location. Dungeness at least has a lot in common with the lunar surface in that the footprints and human influence there, and doubtless in Cape Canaveral too, are extremely durable. Dungeness has been compared to “the surface of the Moon”, and this could equally well be inverted to comparing the surface of a distant planet to Dungeness. Titan in particular springs to mind.

On the whole, the view from moons, planets and asteroids on the Universe is either obscured or clear. There is a strong tendency for conditions to be close to extreme here. Either the sky is completely clear or completely cloudy. This is not universally so. For instance, on Mars clouds do occur but on the whole the sky is empty of them. Earth is cloudier than Mars but not as cloudy as Venus. This is one situation where I may not be aware of conditions outside the British Isles and over much of the planet the sky is either usually clear or mainly cloudy, but there are even so areas where there are, for example, little fluffy clouds in a blue daytime sky. The clouds on this planet are usually mainly water ice or water vapour, but the volcanoes are usually silicate rocks.

It needn’t be this way. Martian clouds are generally either water ice or dry ice, i.e. carbon dioxide. On the outer planets they’re various, sometimes evil-smelling, substances like ammonium hydrosulphide or hydrogen sulphide. On Titan they’re methane, and form a largely uninterrupted deck of obscurity. One notable thing about all these clouds is that none of them actually constitute a substantial part of the world in question’s atmosphere. Our own atmosphere, for example, is not mainly water vapour, and if it was this planet would be very like Venus and completely uninhabitable with no rivers, lakes, seas or oceans, because steam is a much stronger greenhouse gas than carbon dioxide. Likewise with the prominent clouds elsewhere in the Universe. Even so, there are circular storms, thunderstorms and plenty of cloud types approximating our own, as well as the same formations. On Mars, Earth and perhaps elsewhere, a peak can push a body of air up past the point where it starts to form clouds, and on its leeward side chains of clouds can develop in similar manners. This is of course not always so. Rain clouds of any kind whose drops actually reach the ground are only found on Titan and Earth in this star system. Something like snow is more common, but is sometimes the atmosphere itself freezing. Hence when you look at the sky, you’re seeing clouds like those on countless billions (long scale) of worlds throughout the cosmos.

These processes and structures can be composed of less expected materials in other star systems. A particularly easy kind of planet to detect by the method of looking for light being dimmed by a large body passing frequently between us and the star is the “Hot Jupiter”. These are, as the name suggests, somewhat Jupiter-like planets, but differ from our own largest planet in that they orbit their primaries in a couple of days and are far hotter at their cloudtops than any planet’s surface in our own system. Consequently, although they too have clouds “like” ours, they’re actually made of substances like droplets of molten titanium or quartz, or perhaps crystals of the same. Meanwhile, circling the Sun and doubtless innumerable other stars further out than Earth, the converse situation exists, with volcanoes made substantially of water ice and erupting water instead of silicate, while the clouds are made of ice or water vapour instead. This is as extreme compared to a world like Enceladus, Titan or Pluto as the silicate clouds are to us.

Taking the comparison a bit more deeply, the water that erupts out of volcanoes in the outer system emerges from a mantle of flowing slush analogous in the same way to our own rocky mantle, which does flow but is not really fluid as we understand the term as it’s extremely viscuous, but just as far out moons hide internal water oceans beneath a superficial veneer of ice, though sometimes a very thick crust thereof, so does our home world secrete a deep ocean of rock. It’s easy for us to imagine that somewhere like Europa or Enceladus could be concealing a vast reservoir of sea water replete with its own version of fish because we are ourselves familiar with that from our own seas. Extending that to our own mantle, who are we to say that there are no “fish”, perhaps silicon-based, hundreds of kilometres beneath our feet? After all, the ocean of rock is hundreds of times larger than the ocean of water on our home world. This can only be speculation, at least right now, and it’s hard to imagine how it could become anything else. Maybe there is an extremely hot Earth-sized planet whose lava oceans do contain life forms, or maybe not, but we’re looking for “life as we know it” when the one thing we really do know about life elsewhere is that we know nothing of it, or even of its existence.

And perhaps we will never know. Clearly nothing we’re aware of now could rule out the presence of other life off Earth, because we have an example of life here, but although there are numerous reasons we could project onto the sky that might make it implausible, it’s entirely possible that we’ll simply never know if we’re alone in the Universe, and that might apply even if we embarked on an exploration of it. Even if our entire Galaxy proved to be lifeless apart from us, there might be no particular reason for it other than luck, and another galaxy, such as Andromeda, could have life, and if not that a different galaxy so many gigaparsecs from us that we’ll never know it exists. Right now there doesn’t seem to be any kind of mathematical or scientific argument which would be able to give us an answer to this question. It’s rather like the existence of God. You can be “theist”, believing that there is life elsewhere. You can be “atheist”, observing the Universe and the physical laws which decide what can be in it and deciding that life is just a fantastically improbable freak accident, thus committing yourself to the probability that terrestrial life is all there is. Or, you can be agnostic, and simply withhold an opinion on the matter, while holding out for the possibility that there is or is not on a kind of faith-like basis. It’s even possible that we will never know if there’s life within our own planet.

Getting back to precipitation, there is a line from the TV series ‘Wonder Woman’ which seemed highly dubious when I first heard it. A man from the future visits the late 1970s and remarks to her that there are planets made of diamond where a stick of wood would be a previous commodity. At the time I suppose I assumed that other planets were more like our own than they in fact are, because remarkably for such a soft and unscientific franchise as ‘Wonder Woman’, with the likes of disappearing handbags and invisible aircraft, this is in fact so, and you don’t even need to look outside our own star system to find such planets. Both our ice giants are probably so rich in diamonds that they’re as common as icebergs in the Arctic or hailstones on a spring day, and wood would naturally be unheard of. Wood is also associated with life of course, and we have no idea how specific it is to Earth. If it is, it’s like blue john, which only occurs in one place in our Solar System and probably for many light years further than that, in the Derbyshire Peak District.

Water has influenced the appearance of the Peak District in a couple of significant ways which give the area its distinctive character. One is through the erosion of potholes and other caverns and another is the various effects of glaciers, such as causing lakes to form by blocking rivers and the presence of isolated boulders a long way from their original locations. It isn’t clear what actually happened there in that respect during recent ice ages, but it seems that ice-related erosion and weathering relatively close to melting point where ice expands as its temperature falls is likely to be characteristic of Earth as an ongoing process rather than anywhere else in the system, although during certain relatively short-lived catastrophes this does seem to become significant. The difference here is that in many places the temperature has fluctuated around the range where this takes place, making it a dynamic and repetitive process.

Looking up, we may see Cynthia. I’ve been rather startled to find recently that for some reason flat Earthers perceive her as luminous! She looks like nothing so much as a ball of grey rock to me. A varied and beautiful one to be sure, but not luminous. This impression, though, is not confined to our satellite. The other planets in the system do in fact look like bright stars to the naked eye. Even so, there are noctilucent clouds, which are so high in our atmosphere that they reflect sunlight considerably later or earlier than sunset or sunrise. It’s simply that unexpectedly daylit items in the night look so bright by contrast that they’re practically luminous, but not literally so. It illustrates how much the human eye can adjust to light and darkness that Cynthia can appear to shine. Yes, there is moonlight. Also, the light from the white door in our bedroom reflects onto the blue-painted wall, almost bringing us back to Fauvism.

When Sarada became aware that I tended to get bogged down in details, she recommended a book to me which I very much enjoyed: ‘The Mezzanine’, by Nicholson Baker. Baker’s book, which can hardly be described as a novel, focusses on the minutiæ of the quotidian in a manner possibly reminiscent of «A la recherche du temps perdu». Whereas I find the latter unhealthily self-absorbed (though I haven’t read it), the former caught my attention and was easy to relate to. It has no real plot and has been described as having a “fierce attention to detail”. As a young adult, I used to write long descriptions which I couldn’t turn into stories. Fortunately, Baker has succeeded in getting a work using a similar approach published. Most of our experience, mine at least, consists of such thoughts and unfinished mental doodles. One difference is that ‘Mezzanine’ finishes these. The approach taken is somewhat reminiscent of a minor poetic movement of the late twentieth century called “Martian Poetry”.

Martian Poetry is a small and fairly transient subgenre of poetry whose most famous piece is Craig Raine’s ‘A Martian Sends A Postcard Home’. This can be found here. It can take a while to puzzle out, but refers to such things as books, telephones and sleeping together. It’s a series of riddles, but more than that. Published in 1979, it uses unusual metaphors to make everyday objects and experiences fresh and unusual. It’s a little like the real-life ‘Man Who Mistook His Wife For A Hat’ and it raises the question in my mind of who the narrator is. When I wrote the previous post, I realised I’d created a problem. I had no idea who the aliens describing Earth were and I had to come up with a semi-feasible model of their own world, anatomy and physiology before I could begin to portray our home planet. In particular, I had the alternatives of making their comfort temperature hotter or colder than ours, and chose colder because more of our own star system, and in fact the whole Universe, is colder than Earth’s surface rather than hotter. Once I’d done that, I had something I could relate to and a perspective from which to conceive of Earth as others see it. Craig Raine, unsurprisingly, doesn’t do that. We can, however, glean something about the narrator because of the metaphors used, which can be contradictory. For instance, he uses the word “caxtons” to describe books, which he sees as avian, multiwinged creatures. This is a spiky-sounding word with its C and X, and calls to mind a rustly, fluttering thing which one might imagine capable of flight, and certainly it confers that capacity to its reader’s mind, but calling it after the fifteenth century printer anchors it in human life, and even in England. Nor does Craine play fair with the reader when he later describes mist as making the world “bookish”. The problem Craine sets himself is that of not being able to make the narrator Martian enough, because that would seem to make the poem less comprehensible.

I tried fairly hard to find another example of a Martian poet, but all I could uncover was Christopher Reid’s ‘The Song Of Lunch’, and even then I was only able to see the Emma Thompson and Alan Rickman TV movie version. It has a somewhat similar quality but as the action, such as it is, proceeds, it injects elements of plot and tension into the story and is much more conventional. It can currently be viewed here.

What makes these different from my own perspective of seeing a fountain in the park and thinking of the plume on Io’s Tvashtar Patera is specificity. I’m looking at the world in a kind of Cartesian way. I see the parabolas described by the water and consider the similarity, which does make me view them afresh, but there are only specific and sparse details and the comparison is with a specific alien environment. This cognitive estrangement can, however, be broadened and make the whole world surreal. I can remember one guy describing the experience of going swimming as stripping naked, putting on a pair of turquoise pants and immersing himself in a bluish liquid in a large blue room with various other similarly-attired people, and this is indeed surreal, and is more general than the constrained and sporadic examples I’ve mentioned above.

Neurodiversity has sometimes been described as being on the wrong planet, and there’s a website, wrongplanet.net, with this name. But which planet is wrong? Maybe it’s this one. “We” who are neurodiverse might be on a planet which, as a whole, treats us badly and makes assumptions which the rest of us will never be able to guess. This planet could be morally wrong. However, that’s unfair. In fact it isn’t the planet which treats neurodiversity so much as Homo sapiens. And the planet we come from isn’t wrong either. It’s actually the same planet: a conjoined twin Earth with as much right to life as Neurotypical Earth.

That brings us to the Véronique Sanson «chanson» quoted above. The line from Kiki Dee’s English version of the song has always puzzled me – “I feel the rain fall on another planet”. It comes across as a complete non sequitur. Sarada says I’m overthinking it. The original makes more sense: I have undergone such a life-changing experience that I am sensitive to the whole Universe. Now I have a grandchild (and a teenage grand-niece as of the other day, incidentally, which makes me feel really old), and I’m not comparing the experience of considering the Solar System’s other worlds in their own right to losing one’s virginity, but yes I am. I haven’t undertaken a project as grand as the so-called “Grand Tour” because all I’ve done is sit in the living room and typed stuff about the likes of Enceladus, but even that relatively mild enterprise has changed the way I see the world, and we all know about the Overview Effect, so who knows what would await us out there culturally or psychologically if any of our species crossed the lunar orbit?

A Large Terrestrial Planet Orbiting A Yellow Dwarf

After an extensive sky survey covering the planetary systems of a wide range of mid- to high-mass long-lived stars, a number of interesting systems were identified. Although scientists have traditionally focussed on stars suitable for life, with some success, the decision was made to widen the parameters for consideration to larger and more luminous examples in order to prevent observer bias. In particular, a fairly large and hot star was located whose planetary atmospheres showed a number of interesting features. The star was named Sol.

Sol is on first examination not the ideal location for life-bearing worlds. The star itself is considerably more luminous, hotter and more short-lived than our own and there is a notable absence of planets in the habitable zone, occupied by asteroids in this system. Moreover, there is an unusual absence of any planets with the mass of Planet, and therefore moons such as our home world, where life can arise and evolve straightforwardly, are completely lacking. The problems with life arising in this system are multiple. The lifetime of the star is relatively short, the system inside the asteroid belt is above the boiling point of ammonia, which in any case tends to get broken down by the radiation.

In the inner system, there are a large number of moons, all of which are however not particularly hospitable to life. Although three of the four gas giants have large moons, only one has a substantial atmosphere and is too cold for life as we know it to thrive or even appear there. Even so, this proved to be the most hospitable environment and a base was established there from which to mount missions to the other worlds in the system. None of the moons were at all promising. However, just out of curiosity, it was suggested that we investigate the inner system, in spite of its presumed hostility to life.

The situation did not at first appear very promising. There was only one relatively large satellite and even it was too small to maintain an atmosphere. The fourth planet had two small asteroid-sized moons which were even less promising, and the inner two planets had none at all. Two of the planets were large, and of these the outer planet was the host for the single large satellite, although it was considerably smaller than Planet itself. The fourth planet is close to our own world in size but is less dense and has very little to no ammonia on its surface and a tenuous atmosphere incompatible with the existence of most liquids.

Although slightly less hostile than the second planet, the host planet attracted attention because of its rather unpromising moon. It was found that, most improbably, the moon was of such a size and distance from the planet that it would perfectly cover the planet’s star from some locations on the planet, a situation which may well be unique in our Galaxy. This attracted attention to the solid surface of said planet, henceforth referred to as Sol III.

Sol III is a large, hot and rocky planet with a highly corrosive atmosphere and a surface largely covered in an expanse of molten dihydrogen monoxide rock, a substance henceforth referred to by its systematic standard name of oxidane. Runaway exothermic chemical reactions periodically occur on the surface where the likes of thunderstorms and volcanic eruptions trigger destructive processes which it might be thought would completely transform the surface. However, it has been found that in many cases this reaction can be limited by the presence of the liquid oxidane, which prevents dioxygen and the compounds in question coming into contact. Although the atmosphere is mainly (di)nitrogen, over a fifth of it consists of free dioxygen at sea level, becoming ozone some distance above the surface. Although the moon shows captured rotation, Sol III does not, rotating once every 24 hours. This has the consequence of causing the molten rock to flood the margins of the isolated land promontories twice every rotation. Any organism able to survive the extreme heat of most of the solid planetary surface unfortunate enough to find itself in such a location would be swiftly boiled to death by such events. Even away from the lava fields, liquid rock often falls from the sky, so there is little respite elsewhere on the planet.

There are exceptions to these conditions. There is a small area on the west side of one of the southern land promontories where this precipitation rarely or never takes place and many other regions close to the equator where it’s a relatively uncommon event, and these areas are free from the rivers and other bodies which make conditions so hazardous. The liquid is also quite corrosive and somewhat acidic compared to ammonia and tends to eat away at the solid surface of the planet. There are clouds of vaporised rock higher in the atmosphere which sometimes reach ground level. Near the poles the situation is slightly more hospitable, since these areas stay below oxidane’s melting point, and near the south pole temperatures are comfortable through most of the planet’s orbit and relatively normal crystallised oxidane.

Surface gravity is about triple our own, which would make it difficult to tolerate for long, and immersion in liquid would be one strategy to enable us to survive for long periods on the surface Sol is bluer than our own sun, with the result that the landscape, seascape and items within it have a blue tinge. This particularly applies to the lava plains dominating the surface and the sky when free of cloud. The higher gravity also flattens the solid surface, most of which is below the level of the lava, reducing the relief still further.

Considering the oxidane as a simple bulk substitute for our own ammonia, the chief difference between Sol III and our home moon is that the majority of the world is covered by an interconnected body of water, into which streams and rivers tend to feed, unlike our system of independently interconnected lake networks. Its mineral nature is emphasised by the presence in solution of many minerals, partly due to the strongly solvent properties of the liquid. More than half the solid surface is in permanent darkness and only just above oxidane’s melting point, though still far above the levels compatible with life as we know it. Also common here is a manifestation of the even hotter interior of the planet, also found on land, where even the silicate minerals melt and flow like ammonia. The silicate volcanism of Sol III, though, is physically still quite similar to our own oxidane volcanism, except that the volcanoes produced tend to be flatter and have less steep sides.

Technical terms have had to have been invented for the surface features of the planet. The lava fields are referred to by the arcane classical term “ocean”, and the giant island promontories as “continents”. Although the ocean is a single entity, there are also lakes on the surface which are not linked to them. These tend to be purer oxidane because of the reduced volume and time available to dissolve the underlying rocks. The ocean itself is conceptually divided into four sub-oceans, referred to as “northern”, “western”, “eastern” and “southern”. Currents running along the last three also mean that there is in a sense a further ocean not separated by land from the others. There are six continents. A relatively hospitable one is situated in the southern polar region, where the temperatures remain low enough for practically the whole surface to be lava-free. The corrosive atmosphere and high gravity, of course, remain. Most of the surface from the northern coasts of the polar continent is molten although the smallest continent, referred to as “Southern” is relatively free of precipitation. There are then two triangular continents, both linked to northern ones, referred to as “West Triangle” and “East Triangle” . The larger one, East Triangle, has two large areas free of precipitation but like Southern is extremely hot. West Triangle has a small stretch with practically no precipitation. Adjoining East Triangle is the Great Continent of the northern hemisphere. This is the largest continent of all, and its northeastern region is again cool enough not to kill someone quickly. The same is true of the final continent to be mentioned, the Lesser Northern Continent, although this and the Great Continent become very hot nearer the equator.

The surface of the planet is young. Unsurprisingly, the oceans are in constant motion, but the oxidane also eats away at the solid surface over a much longer time scale, although the occasional catastrophe can make major changes very quickly. WInds are another significant erosive factor. Also, in a process not found on our home world, the surface as a whole is constantly remodelled over a period of millions of years and the continents move around, collide with each other forming island chains and mountain ranges and split apart. This is, however, a very slow process. One consequence of this along with the erosion is the near-absence of impact craters.

A paradox of Sol III is how such a hot planet with a highly reactive atmosphere can remain in a fairly stable state rather than all the dioxygen reacting with the surface rocks and being removed from the atmosphere. The solution to this is quite remarkable: there are two balanced biochemical processes, one combining oxidane and gaseous carbon dioxide into energy-storage compounds with the aid of stellar radiation which releases the toxic gas as a waste produce, and another which combines the energy-storage compounds with dioxygen and releases carbon dioxide. Things were not ever thus. The planet went through a stage early in its history at an equable temperature, though still higher than our home world, with a harmless and hospitable atmosphere. Then, a certain group of microbes developed a mutation causing them to release the poisonous gas and the pollution of the atmosphere killed much of the biosphere. Hence not only is there life on the planet, in profusion in fact, but it actually requires the extreme high temperatures, molten lava and toxic atmosphere to survive. Although there are a few less extreme environments on the surface free of oxygen, all life on the planet uses molten oxidane to survive. Only a very few species could survive at temperatures we would consider comfortable or even survivable, and at such temperatures they’re in a dormant state from which they can only emerge in conditions of extreme heat. There is no true overlap between conditions life on Sol III would find tolerable and our own definition of survivable conditions.

Leaving microbes aside, some of which have biochemistry a little closer to our own with the proviso that they don’t employ ammonia, the larger organisms on the surface fall into three categories, which are covered below. It might be thought that the high gravity would make a buoyant environment more suitable for life, and in fact there is indeed more life living within the oxidane than out of it, there is also plenty of life outside these conditions. Although land life on Sol III tends to be smaller and stockier than the kind we’re familiar with, it’s as diverse and widespread as it is on our home world. One difference is that our own life originates from three different stocks due to our independent lake networks, whereas all life on Sol III is related because it originated in the ocean, or at least spent a long time evolving there before becoming able to leave it and exploit other niches.

One form of macroscopic life tends to use a prominent green pigment to absorb red light from the star to drive a nutrition-synthesising process. Its reliance on red light may reveal how life on Sol III is at a disadvantage compared to life on worlds near to redder stars. It’s this process, known as photosynthesis, which was responsible for poisoning the planet and causing the extinction of most life forms earlier in its history. Most large organisms reliant directly on photosynthesis do not move much of their own volition and the terrestrial varieties often bear colourful genitals which attract motile organisms to bear their semen to other members of their species and fertilise their eggs.

Another form of life tends to be able to move of its own accord and survives by consuming the bodies of other, often living, organisms. Their anatomy and physiology is usually centred around their need to move dissolved gases around their bodies, which they often manage using a system of tubes and one or more pumps. Their reliance on dioxygen and need to remove carbon dioxide gas from their tissues necessitates that all of their bodies need to be in close contact with a respiratory fluid, and all of the larger organisms also have entire body systems to deal with gases, either dissolved in the water around them or present in the air. In the case of the dominant class of animals, as they are known, on the land, this has limited their size as they rely on tubes open to the atmosphere. Incredible though it may seem, most animals can’t survive more than a few minutes without a constant supply of dioxygen.

The third form of life forms a kind of bridge between living and non-living parts of the food chain. Like the photosynthesisers, these are largely sessile and immobile, and tend to live off a substrate consisting of the dead or diseased bodies of other organisms. They do not photosynthesise. Many of them consist of subterranean mats of fibres which produce occasional fruiting bodies above ground level. Some of them are also parasitic. Without this group of organisms, there would be an ever-increasing unusable biomasse which would eventually cause all advanced life on Sol III to grind to a halt.

Animal evolution on Sol III went in a somewhat surprising direction. Unusually, a particular kind of fluid-living animal developed a hard internal skeleton and its descendents were able to use it to aid their movement rather than the more usual arrangement of holding them in place. These have proliferated into a variety of forms, though they constitute a small minority of species on the planet and animals themselves occupy much less biomasse than the plants (the photosynthesisers). Of all these species, one rather large, by the standards of the planet, type has become dominant over the planet through a technology based initially on the use and control of the runaway oxidative reaction and the discovery of language, which is acoustic and mediated by means of the organs which evolved to exchange gases. Remarkably, in spite of the intense gravitational field, these animals are able to achieve an erect bipedal gait.

It should be noted that the pace of animal life on Sol III tends to be very frenetic. This seems to be due to the high temperature and the employment of dioxygen as a means of releasing chemical energy. This hyperactivity doesn’t apply to plants to the same extent. It’s all the more so for those animals whose bodies rely on their own heat to drive their metabolism, and unsurprisingly this includes the technological species. Dormancy is a less significant phase of life for many animals living on the planet, partly because the years are shorter and in many parts of the world the seasons are less extreme. However, many species do become dormant on a diurnal basis for a considerable fraction of the planet’s rotation period, often when it faces away from the star, and depriving them of it for surprisingly short intervals leads to increasing mental derangement. The need of such organisms for food, oxidane and their respiratory gas is quite extreme compared to our own. This constitutes a barrier to space travel, as it means they are unlikely to be able to survive interstellar space voyages as easily as we can. This may not be a bad thing because there is a tendency for some members of the species to be quite violent, but this is also likely to be self-limiting. However, it’s probably better not to speculate too much about this aspect of their nature without more data.

One major lesson to learn from the complex life present on Sol III is that we may have restricted views on what constitutes an hospitable environment for the advent and evolution of advanced life forms. Before this discovery, the proposal that a sophisticated biosphere could exist on a planet two-thirds covered in molten rock with a dense caustic atmosphere capable of eating through metal, with a high gravitational field and temperatures far above boiling point over most of its surface, circling an ageing Sun much hotter and more massive than our own would have seemed ridiculous to all. These life forms can not only tolerate living with acidic molten rock in an aggressively reactive atmosphere but have evolved in tandem with it to the extent that depriving them of the gas for more than a few minutes is uniformly fatal and they need a continual intake of liquefied dihydrogen monoxide to survive more than a couple of rotations of their home world. Who knows what the inhabitants of Sol III might consider suitable conditions for life given their own extreme circumstances?

Any resemblance to Arthur C Clarke’s ‘Report On Planet Three’ is not entirely coincidental.

Are We Out In Dullsville Now?

If you go back to where I started this series properly, you’ll find that I produced a post, whose name and location I’ve currently forgotten, introducing the Solar System from the outside in. I’ve now returned to the outermost part of the system except for the Oort Cloud, and I ask myself, are these outer reaches really dull? Well, they are in a literal sense of course, in that the Sun is pretty dim at this distance, but the wide separation, small size and low temperature of worlds, if that’s the right word for them, combined with the facts that nothing has ever visited them and that they’re hard to detect, means that they might also be exceedingly boring. I can imagine people travelling to them who want to get seriously away from it all, and from other people. In fact, there’s a scene in an Iain M Banks novel about someone who has done precisely that. I think it’s ‘Excession’.

There’s a lot going on in the regions near the Sun, and I use “near” quite loosely as I intend for it to apply to Jupiter and Saturn, the latter being well over a milliard kilometres from it. Incidentally, why is it we get stuck at kilometres? I’ve just fished out an obscure English word to describe a distance which could easily be referred to as a terametre, and yet we never say that. The further out one goes, the less is happening, with the occasional exception such as Triton’s liquid nitrogen geysers and the mysterious brightness of the surface of Eris. Average distances between worlds increase, temperatures plummet and the Sun looks ever dimmer. That said, it’s still possible, for example, to imagine a world so cold that it has oceans of helium II which crawl over its surface and climb mountains, or outcrops of superconducting alloys which generate incredibly powerful magnetic fields. I don’t know if either of those things are possible, because the 3K background temperature of the Universe might rule them out and helium only becomes superfluid at 2.17K, but there have always been surprises. Few people would’ve guessed that Neptune has winds which blow faster than the sea level speed of sound, for instance. Perhaps high winds on a very cold planet would cool it below the temperature of deep space.

Considering the history of the Universe, a frantic and hyper beginning slows down continually, through the current stelliferous era and other less and less eventful stretches of time until basically nothing is happening. Space is rather like this too. Not a lot goes on in the Oort Cloud.

Even so, there is stuff out there. For instance, there’s a planetoid nicknamed FarFarOut, which is 132 AU from the Sun. Also known as 2018 AG37, FarFarOut is about four hundred kilometres across, which means it could be round. It actually swings round to being only 27 AU, closer than Hamlet. It takes 718 years to orbit and at its maximum distance of 132.7 AU the Sun is almost 18 000 times dimmer than from here. There’s also 2019 EU5, which averages 1 380 AU from it and has a maximum distance of 2 714 AU. These figures are highly uncertain, but if the aphelion is correct (it could be considerably greater or less), sunlight at such a distance is finally weaker than our moonlight and the planetoid takes fifty-one thousand years to orbit the Sun at a mean velocity of about eight hundred metres per second. With such planetoids, it becomes difficult to judge their actual trajectories because they move so slowly and haven’t been observed for long.

There are now five human-built spacecraft out there: Pioneers 10 and 11, Voyagers 1 and 2 and New Horizons, the last being the newcomer, only launched in 2006. Voyager 1 was manœuvred out of the ecliptic so it could get a good view of Titan, and is therefore heading out into the scattered disc rather than the Kuiper belt. It’s 153 AU from the Sun at the moment. Voyager 2 is 130 AU out. Both were launched in 1977. The Pioneer probes have been going for rather longer but are actually closer, at 129 and 108, but they’re all now over twice as far away as Pluto ever gets. New Horizons is a mere 50 AU from the Sun right now. Now a viable claim is made that the Voyager and Pioneer probes are now in interstellar space because the pressure of the solar wind is weaker than the ambient “flow” (I suppose) of charged particles between the stars, but there are still planetoids orbiting out there, even ones which never dip into the volume inside the heliosheath. Isaac Asimov’s novel ‘The Currents Of Space’, though its science is out of date, uses the idea of similar flows as an important plot point, so this is one possible way in which the outer part of the Solar System might not be boring. Processes taking place within the heliosheath which influence planets, asteroids, moons and so forth would not operate beyond it. For instance, any magnetospheres which exist out there would not be thrown into asymmetry by the solar wind, and larger and denser atmospheres could exist out there, although the only elements able to maintain a gaseous state at such temperatures would be hydrogen and helium, and in fact ultimately helium. It also means the useful isotopes found in lunar regolith would be absent from many trans Neptunian objects and this reduces the utility of mining for them.

There are a dozen known planets, dwarf planets by the IAU definition of course, which reach 150 AU or more from the Sun. This is one motivation for not calling them planets. If they were, they’d now outnumber the major planets. The same is, though, also true of asteroids and centaurs, and asteroids were simply called “minor planets”. The whole thing seems a bit silly and solves a “problem” which had in any case already been sorted when such concepts as major and minor planets, or planetoids, were invented to address the issue after the discovery of Ceres, in the early nineteenth century CE. Right: I’m going to resolve not to go on about this for the rest of this post as I’m sure it’s getting old. These objects include Haumea, Quaoar, Eris, Sedna, Makemake, Albion, Gonggong, Pluto itself, Varuna, Arrokoth, Arawn, Chaos, Ixion and Typhon. Others are also named, but most don’t come up much in discussions or news, and most of them have provisional designations. To be honest, some of them just stick in my mind because of their names, particularly Quaoar but also Makemake and Gonggong. FarFarOut has a predecessor which isn’t so far out called FarOut. There are two zones: the Kuiper belt, which consists of objects orbiting near the plane of the inner system, and the Scattered Disc, comprising objects whose orbits are more tilted. The second category developed because of the gravitational influence of the outer planets, although it occurs to me that this might also be the region where the Sun’s influence and the traces of the solar nebula become less relevant to them. There is also a third region, the Oort Cloud, which is in really deep space beyond either of the others, whence some comets originate, and extends for over a light year in every direction. TNOs are also distinguished by colour (Eris springs to mind but that’s a special case as far as I know). They’re either steely blue or bright red. A classification kind of cutting across this are the poorly-named “hot” and “cold” categories. Cold TNOs orbit close to the ecliptic and are usually red. Hot TNOs have tilted orbits and range between the two colours, which means that the red ones are the “cold” ones.

By Pablo Carlos Budassi – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=94143935

One of the weirdest known trans Neptunian objects is Haumea, illustrated above. This has three remarkable features. It has a ring, two moons and is ellipsoidal but far from spherical. It counts as a dwarf planet. Its unusual shape is called a Jacobi ellipsoid, and is rather surprising. It intuitively makes sense that a rapidly-spinning body would be thrown outwards at its equator and therefore assume a kind of tangerine shape, or perhaps even a discus shape, as seen clearly with Jupiter and Saturn but also with most major planets including Earth to some extent. Venus and Mars are somewhat different, the former being almost spherical and the latter having a more egg-shaped form due to the Tharsis bulge. This more intuitive shape, an oblate spheroid, is quite common and the torus is another quite remarkable stable shape which, however, is hard to envisage actually forming in the first place. There is a notorious (to Sarada and me) pebble classification system called Zingg (two G’s), which divides them into spheres, discs, rods and blades according to their X, Y and Z axes. This used to be a source of joy to us due to its apparent obscurity, but has its uses, and Haumea counts as a blade. Each axis is markèdly different to the other two. Lagrange, who discovered the points of gravitational equilibrium around pairs of masses responsible, for instance, for the trojan asteroids in the orbits of several major planets and the trojan moons in the Saturnian system, held that the only stable shape for a rapidly rotating body of a certain size was the oblate spheroid, but counter-intuitively, this turns out to be wrong. This is the gateway to a whole branch of geometry involving ellipsoids.

Haumea’s axial dimensions are 2 322 × 1 704 × 1 138 kilometres. It spins once every three hours and fifty-five minutes, which is particularly high considering its size. Comparing it to Pluto, for example, that planet takes six and a half days to rotate and has a diameter of 2 377 kilometres. Not only is Haumea considerably smaller and less massive but it also spins three dozen times faster, causing a much stronger centrifugal effect. I have to admit that not only is it entirely unclear to me why Haumea is this shape beyond the simply fact that it’s spinning really fast and has thereby had projections drawn out from it, but also I can’t understand the maths behind it. If this can happen once, maybe there are larger planets out there somewhere with the same shape, maybe even Earth-sized ones. It seems unlikely, at least because a larger object would tend to be more spherical, although there could be other reasons why it might happen such as a nearby massive body pulling it out of shape. Haumea was probably hit some time in the past by something which sent it spinning wildly. It also isn’t clear that it’s reached hydrostatic equilibrium although it’s very large for a solid object if it hasn’t.

Haumea is the Hawaiian goddess of fertility and childbirth. The planet’s moons are named after her daughters, Hi‘iaka and Namaka. It’s thought to be rocky with a surface layer of water ice and seems to have a red crater near one of the geometric poles (i.e. on the equator). I’m guessing the reddish colour is due to tholins. Haumea seems denser than most other Kuiper belt objects, including Pluto, and may be as dense as Mars or Cynthia. It has crystalline water ice on its surface even though its temperature ought to cause the ice to become glassy. There may also be clay on the surface, and cyanides of various kinds. Hence the very surface would often be highly poisonous to ærobic life forms, including humans. There is no methane, suggesting that it was boiled away in the heat of impact.

The ring spins once every twelve hours, in other words a third as fast as the planet. The moons are small and probably result from the collision. Another thing which probably results from the collision is the Haumea family. In other parts of the Solar System, there are various families of objects, for instance the Vesta family, which consists of Vesta plus the asteroids which have been chipped off it, including some meteorites which have arrived on Earth. The Haumea family is the only identified group of objects beyond Neptune, and originates from the collision. They’re all water-ice at the surface and are fairly bright. Some may be up to seven hundred kilometres in diameter and count as dwarf planets in their own right. They average between forty-one and forty-four AU from the Sun. One of them seems to be in the family but is red.

Haumea itself is 43 AU from the Sun on average and has an orbital eccentricity of a little under 0.2. It takes 283 years to traverse this orbit, so it isn’t enormously further away than Pluto and in fact it gets closer to the Sun than Pluto does.

Another name which sticks in the mind belongs to the dwarf planet Sedna. This is one of the reddest known objects in the system and is also tied with Ceres in being the largest moonless dwarf planet. Sedna is one of those planets which makes me wonder whether it’s one of many undiscovered ones, because it was discovered due to happening to be almost as close as it gets to the Sun at 76 AU. Even that distance is almost twice Pluto’s. It takes 11 400 years to orbit the Sun and gets out to five and a half light days from it. The last time it was there, there were mammoths on this planet and the pyramids had yet to be built. It’s around a thousand kilometres in diameter, like Ceres. It’s named after the Inuit goddess of the sea and its denizens. The extremely elongated orbit, which has an eccentricity of almost 0.85, could be explained by the presence of an extremely distant and large planet. It’s part of a class (as opposed to a “family”, as in the Haumea family) of objects whose perihelia are greater than 50 AU and mean distances over 150 AU from the Sun. These orbits have an eccentricity of around 0.8, so although that’s the definition, in actual fact they’re considerably more elliptical. It’s been established that there are no large planets in the system beyond Pluto to a considerable distance, although there is the question of a missing ice dwarf. That would, however, not be detectable by current methods and wouldn’t explain the sednoid bunching of orbits. It’s also been suggested that the sednoids move thus because they were influenced by nearby stars back when the Sun was young and part of a cluster of baby stars. There are occasional stars which seem to be almost twins of the Sun due to similar proportions of heavier elements (often referred to in astrophysics as “metals”), suggesting that they were once our companions. Alternatively, they may have been captured from those stars early on in the history of the system. The other two objects falling into this category are Leleakuhonua and 2012 VP113.

As well as the usual tholins, Sedna is covered in frozen nitrogen and methane, which is present generally but absent from Haumea, probably due to the collision. Its orbit looks like this to scale:

By Tomruen – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=60453344

There may be amorphous carbon on the surface. Unfortunately the term “amorphous carbon” is ambiguous as it can mean charcoal- or soot-like carbon, which in fact consists of graphite sheets haphazardly arranged, or it can literally mean amorphous, i.e. glass-like, carbon, which might have special properties such as being a high-temperature superconductor and being harder than diamond. I suspect they mean the former – just a load of boring old black gunk like you might dig out of a coal mine.

Sedna is special because it isn’t. It’s probably an example of a very numerous class of objects orbiting way out beyond the influence of Neptune in the Oort Cloud. We happen to know it’s there but there are likely to be many, many more examples way outnumbering the objects known in the inner system whose orbits haven’t so far allowed us to detect them. That said, the presence of tholins is related to the influence of solar radiation so it might not be typical of them.

Another planetoid is Arrokoth, unique in being the only trans-Neptunian object other than Pluto-Charon and their moons to have been visited by a space probe, New Horizons. It was nicknamed Ultima Thule, but this was later deprecated due to the association with Nazi occultism. It was actually named in a Pamunkey ceremony. The common “dumb bell” appearance shared by two of Pluto’s moons, some comets and other objects is also seen here. It’s thirty-six kilometres long altogether but consists of two smaller fused planetesimals, fifteen and twenty-two kilometres in length. Planetesimals are the bricks which make up planets and moons, and have never been seen in their raw form before. If a twenty-kilometre object is typical, Earth would be made up initially of over a hundred million of them, having long since melted together and lost their identities. There are interesting substances on its surface, including methanol, hydrogen cyanide and probably formaldehyde-based compounds and complex macromolecules somewhat similar to those found in living things. The basin in the foreground, which is probably a crater, is a bit less than seven kilometres across and called Sky. The axis of rotation passes through the centre of the dumb bell.

Arrokoth is a “cubewano”. These are named after their first discovered member, 1992 QB1. Also known as “classical Kuiper Belt objects”, cubewanos are often in almost circular orbits less than 30°from the plane of the Solar System, but are also often not. They have years between 248 and 330 times ours, the lower limit being defined by the plutinos with their sidereal periods close to Pluto’s. I’ve mentioned them above. They’re distinctive in not being particularly distant (relatively) and also not having orbits connected to Neptune’s.

Quaoar is a particularly large cubewano. Its name is from an indigeous people called the Tongva in Southwestern North America, although for a time it was called “Object X” as a reference to Planet X and because its nature was unknown. You can see the planetary definition crisis developing here, as it was discovered in 2002. It was first imaged in 1954, but like many other bodies went unnoticed for many years. It takes 289 years to orbit the Sun and is 43 AU from it. It seems quite dark, suggesting that it’s lost ice from its surface, which has a temperature of -231°C. It has a moon to keep it company, like many other trans-Neptunian objects. The diameter is around 1 100 kilometres.

Previously, the largest known TNO was Varuna, discovered in 2000. This may also be a “blade”-shaped planet like Haumea, and is just barely beyond Pluto’s average distance from the Sun at 42.7 AU, taking 279 years to orbit. It seems to be less dense than water and its average diameter was recently estimated at 654 kilometres. It takes six and a half hours to rotate on its axis.

I feel that this series is now drawing to a close. However, there are many objects I haven’t considered, such as the Neptune trojans, the possibility of Nemesis and the question of what large objects may be swimming out there in the depths of the Oort Cloud. There is also one planet I haven’t given its own post. It’s a small blue-green planet, third from the Sun, and will form the subject of my next post.

Pluto’s Kingdom

In the furore following from Pluto’s demotion after Eris’s discovery, a few people argued that Pluto of all places deserved to be called a planet because it had a moon. In fact it has at least five: Charon, Kerberos, Hydra, Nix and Styx, not in that order. It certainly seems to make sense that if a world is hefty enough to have its own companions, it ought to count as a planet, but in fact that isn’t how it works, and there are actually a couple of reasons why having moons almost makes a world less planet-like, if by “planet” you mean a solid or fluid spheroidal body with a relatively strong gravitational pull.

Only two of the universally accepted major planets have no companions: Mercury and Venus. These are notably the two next to the Sun, so the reason may be that they lack the gravitational “oomph” to maintain them. Matter circling either wouldn’t have to be very far out before it felt the Sun’s pull more strongly than the planets’. That said, both of them have respectable gravitas of their own and are far more than just a bunch of rocks loosely bound together. This last is the point really. A small object is less able to hold itself together and is therefore more likely to be a collection of stones or chunks of other matter, highly porous and riddled with caves and liable to lose some of itself or not accumulate nearby bits of matter in the first place. Therefore, in a way, if a body has a few moons, this could be more a sign of it not being a proper planet rather than the other way round. The other reason is basically the same but proceeding from the other end. Many Kuiper Belt and scattered disc objects are binary, and quite possibly more than binary. The same is true to a lesser extent of the asteroids. Being binary is therefore a characteristic of agglomerations of matter which are too small to hold together, but confusingly, having moons is also a characteristic of large planets able to pull loads of stuff towards them which is either already in clumps or forms into planet-like worlds in their own right. Hence Pluto having five moons, one of which is very large indeed compared to the planet (yes, planet) itself, doesn’t count towards its possible planethood.

All this aside, Charon is so large that if it orbited alone it would definitely count as a planet, at least if Pluto does. Earth is notorious for having an unusually large moon, if moon it be, of an eighty-first of its density. Charon far outdoes this, and in doing so consequently outdoes all the other planets in this respect, whose moons are generally well under a thousandth of their mass. Charon’s mass is a little under an eighth of Pluto’s, which is deceptively small as it should be remembered that the diameter relates to the cube root of this figure. After all, Cynthia is a large disc in our sky because it’s a quarter of Earth’s diameter, not 1/81. If the ratio applied to Cynthia and Earth, the former would be considerably larger than Mars, and it might even be habitable, which raises the question of whether such double habitable planets exist out there somewhere. Charon is 1212 kilometres in diameter. Cynthia, like many moons, always shows the same face to us, and the same is true of Charon and Pluto, but in their case the situation is mutual. Both worlds face each other at all times.

I’ve allowed Charon to be overshadowed by Pluto in my own mind, and know relatively little about it. The story of its discovery and naming is quite remarkable. The mythological figure Charon is of course the entity who ferries the souls of the dead across the River Styx into the Underworld, and Pluto being king of the aforementioned domain, one might fancy that the motivation for calling the moon that was clear. However, this is not in fact so. The man who discovered Charon, James W. Christy, actually named it after his wife Charlene Mary, whom he calls Char, and had no idea that the Ferryman was called that too. This gives me pause for thought, because it doesn’t seem to work like one would expect it to naturalistically. It’s reminiscent of the fact that before Saturn was believed to have rings, saturnine herbs were those which had prominent rings, and it’s almost as if the names of celestial bodies are “out there” waiting to be discovered rather than invented, like the non-existent American states of Jefferson and Superior. I won’t dwell too long on this here, but a similar phenomenon is manifested in western astrology where hypothetical planets have been used which have turned out to be real, particularly Pluto.

On 22nd June 1978, Christy noticed that his image of Pluto was not circular, and also that it changed shape on a regular, predictable basis:

Pluto appeared to have a lump on its side which appeared and disappeared. Since the planet is far too big to be irregular, it was correctly concluded correctly that it has a moon, and that that moon takes almost six and a half days to orbit Pluto, or rather, that the two of them take that long to orbit each other. Of all moons and planets in the system, other than small irregular ones, Pluto and Charon are respectively the first and second largest worlds in their companion’s skies, even larger than the Sun in Mercury’s sky (which actually isn’t that large though). Due to captured rotation, that’s also the day length for both Pluto and Charon, and it makes Pluto the only planet to have captured rotation with its satellite, to the extent that it actually counts as a planet, not because of the IAU but because it’s binary and almost orbits Charon rather than the other way round. Axial inclination can also be guessed at fairly reliably with this because the two are likely to circle over each others’ equators, and it’s 57°, exceeding 45° and leading to different variations in day length and the like for the two. Any tilt over 45° involves a peculiar set of circumstances where the polar circles are closer to the equator than the tropics are, though at such a distance from the Sun it’s questionable whether it makes much difference. One thing which definitely does make a difference on Pluto is the atmosphere snowing onto the surface in the autumn and evaporating again in the spring, bearing in mind that the dates for these are more than a dozen decades apart. Speaking of dates, there are 14 205½ Charonian (or Plutonian) days in their year.

The two share many characteristics. Some of these are also shared with Triton, which is closer to Pluto in size and mass than Charon is, but the conditions on the two are even more similar because of their gravitational influence on each other and being the same distance from the Sun, having the same axial tilt and day length and so forth. It’s actually slightly awkward to talk about Charon separately from Pluto, but I’ve written quite a bit about the latter already and don’t want to go over it again. New Horizons managed to take photos of the two together, like this:

This picture is a bit misleading, as it’s effectively taken through a telephoto lens. It wouldn’t be possible to see this similarity near either world because the two are almost 20 000 kilometres apart and Charon is considerably smaller than Pluto even though they are closer in size than any other planet-moon combination. Even so, Charon is notably duller and has a reddish cap over its north polar region, whereas Pluto’s is closer to its equator. This red substance is, however, the same, and seems to have been shed from Pluto and deposited on Charon. Unsurprisingly, it consists of tholins, which are as I’ve said before an organic mixture of dark red tarry stuff which reminds me of the deposits made by herbal tinctures, partly because they actually are quite similar. Tannins in particular spring to mind. To repeat myself from elsewhere on this blog, tholins are the alternative route taken in the Universe by organic chemistry to organic life. The question of how often organic chemistry becomes biochemistry is another question, but there are clearly countless examples of tholins in the Universe judging by how many there are orbiting the Sun. Methane is also deposited on the surface from Pluto. Before any of the stuff gets there, though, it’s been part of Pluto’s atmosphere, and is therefore deposited faster near perihelion. Also, we finally get an answer to why trailing hemispheres are more heavily coated than leading ones: it’s because of gravity. Trailing hemispheres simply bear the brunt of falling material because the material has fallen further by then. The north cap is called Mordor Macula, “macula” meaning “spot”, as in “immaculate” – “spotless”.

Unlike Pluto, whose surface is largely solid nitrogen, Charon’s surface away from the tholin cap is mainly water ice but there are also patches of ammonia hydrates. Also unlike Pluto, there is effectively no atmosphere, so the snowing and sublimating processes on that planet don’t occur here. The south pole is also rather dark, but the north is darker. Although Charon doesn’t have a persistent atmosphere, substances on its surface do sublimate, becoming gas. It’s just that its gravity isn’t strong enough to hold on to any of them. The southern polar region was actually imaged with the help of “plutoshine”, as it was night time there when New Horizons visited, so image processing involved removing the tint of Pluto’s light to restore it to how it would’ve looked if sunlit.

Charon does actually seem to be geologically active, with geysers similar to those on Triton, shedding water ice and ammonia nitrate. This must’ve happened last less than thirty millennia ago, probably a lot less, because the ice deposits are still crystalline and haven’t changed to the glassy form expected after such a long period of time. The different composition of the geyser plumes also means that the moon is different beneath the surface and has geological layers, which was previously controversial as it is quite small. It’s likely that the moon is geologically active due to Pluto raising tides within it, a possibly mutual process, which raises the question of whether there’s substantial heating and an internal water ocean, which it’s becoming apparent is very common in the Universe. Scientists believe that in the distant geological past, it did indeed have an ocean within it but that this froze and expanded, leading to the formation of the enormous canyons visible on its surface in the image at the top of this blog post. This is one way in which water, as a geologically significant compound, behaves differently and leads to different land forms than other substances which melt and freeze. On Earth, water is currently not often a geologically significant “rock”, except at high altitudes and within the polar circles. Beyond the frost line of the Solar System, it often is, and unlike the other liquids, which are often gaseous at Earth-like temperatures, it expands on freezing, leading to geology very unlike ours. Although there are some other substances which expand on freezing, such as bismuth and gallium, they don’t generally occur in bulk. In the case of Charon, water ice is a major and significant mineral which contributes to the landscape and interior in a way something like silicate or carbonate rock does on or in Earth.

More precisely, the reason for those canyons is that as the interior of the moon froze, it expanded and fractured the surface, leading to the formation of a number of features referred to as “chasmata” – “chasms”. These include Tardis, Serenity, Nostromo, Caleuche, Mandjet, Argo and Macross. Many of these have a rather obvious naming scheme, which is fun. Caleuche, which is named after a mythical boat which sails the coast of Chile collecting the souls of the dead, is a Y-shaped canyon thirteen kilometres deep, among the deepest chasmata in the system. Mandjet is thirty kilometres wide, four kilometres deep and 385 kilometres long. Serenity is two hundred kilometres long as a chasma but runs an additional two hundred as an unpaired escarpment. All of these chasmata run around the moon’s equator, separating the northern Oz Terra from the southern Vulcan Planum, which is named after Spock’s planet. Oz is a kilometre higher than Vulcan over its whole surface. Both Oz and Vulcan extend across into the portion of the moon which was dark when New Horizons got there, but it seems likely that each occupies an entire hemisphere. Vulcan is less heavily cratered, suggesting that there’s recently (relatively) been geological activity there which has erased them by remodelling the surface. However, there are some craters and also central mountains, including Kirk and Kubrick. Spock, Sulu and Uhura are also represented thus, as well as Clarke (Arthur C Clarke). The entire area seems to have been covered by a large flow of liquid over the entire hemisphere, probably water.

Other craters include Vader, Pirx, Alice, Organa, Dorothy, Nemo, Skywalker, Ripley, Revati, Sadko, Nasredin, Cora and Kaguya-Hime. I do wonder how people whose religion includes some of these figures feel about the avowèdly fictional characters represented here, but perhaps the day will come when the Vulcan and Jedi world views become official religions too, if they haven’t already. There is another macula, Gallifrey, through whose middle Tardis runs. This means, oddly, that the confusion the Bi-Al Medical Foundation receptionist shows in the ‘Doctor Who’ adventure ‘The Invisible Enemy’ could be explained in a fangirlish way by the presence of this feature, which creates an Ontological Paradox similar to the one created by K-9’s motherboard, introduced in the same episode.

That, then, is Charon, which deserves considerable attention as the largest and best-known of Pluto’s moons. However, there are four more to be covered, and this raises a question: how do they orbit? All other known satellite systems with more than two members consist of a relatively large planet and a number of much smaller moons, and although the orbital dynamics can be somewhat peculiar, such as coörbital moons regularly swapping positions, Pluto-Charon is a different matter. There are two relatively similar masses and other moons in the immediate vicinity. It was calculated at one point that there could be stable orbits in such a situation if an object was at least 3.5 times closer to one mass than the other or if it was at least 3.5 times the maximum separation between the pair, and there are also improbable but stable orbits of various kinds between them such as a figure of eight. Ternary star systems usually have two close companions and a third, much more distant one: this is true, for example, of the Centauri system, where Proxima is much further away than A and B are from each other. The Pluto-Charon system is unique as far as is known in the Solar System in this respect.

Where, then, are the other moons?

This is an image taken by the Hubble Space Telescope three years before New Horizons reached Pluto, and was used to plan the mission. It’s notable that Charon and Pluto actually look fainter in this image than Hydra and Nix, or at least smaller. Styx doesn’t seem to be far away enough to maintain its trajectory. This picture shows that the moons are outside the Pluto-Charon region, separated by a small gap but all relatively close to each other, in an arrangement which reminds me slightly of the TRAPPIST-1 system where several planets are within the habitable zone. They don’t seem to be spaced any way like the Titius-Bode Series and although there is a space between the inner two and the rest, the relative distances of the others are not like those of ternary stars. It also raises two questions in my mind: is this similar to how planetary systems might be arranged around binary stars? Also, is this where Earth’s other moons would be if we had any?

There’s a further surprise. At least two of them are merged double moons themselves, namely Hydra and Kerberos. Going off on a tangent for a moment, bearing in mind that scientists now have sufficient reliable information to establish that two of the small moons of Pluto are former double moons, what the heck do flat Earthers and people who believe, and I quote, “space is fake” think is going on here? Why would NASA, other space agencies and the global astronomical community bother to put in that kind of detail about an entirely bogus cosmos? On the other hand, it is also true that esoteric blind alleys have been known to become highly elaborate, so maybe they think it’s along those lines. Also, fictional universes can be very intricate too. It just strikes me as highly implausible that something like this would be made up and makes me wonder about how flat Earthers think.

Anyway. . .

Hydra and Kerberos are former double moons, and this is evident from their shapes. This is Hydra:

This shape is similar to the comet being studied by the Rosetta probe, and in the comet’s case it’s thought to result from the merging of two bodies. This is that comet, known as 67P:

In the comet’s case, it’s been suggested that the shape results from the heat of the Sun eroding the nucleus. However, each lobe has concentric strata, suggesting that it was originally two bodies which got stuck together. Were it only one, it would have layers indicating a former, more regular form. Hydra is fifty-one kilometres long. Like all the small moons, Hydra is shiny with water ice, and is the outermost moon at a distance of 64 738 kilometres from the barycentre, which is outside Pluto. It’s probably receded from Pluto-Charon due to tidal forces. The name is a bit unusual and sticks out because it isn’t named after a humanoid mythological figure, and this principle also applies to the next moon in.

Which is Kerberos, named after the four-headed (the snake forming the tail has a head) guard dog of the Greek Underworld. Isaac Asimov once suggested that the tenth planet should be called Cerberus so that a mission approaching the Solar System from the great beyond would encounter the system’s guard dog first. To that end, it makes more sense that Hydra be called Kerberos and since the latter was already known to be closer to Pluto than Hydra when it was discovered, its name lacks elegance in a way. There are no good images of the moon:

This image gives the impression that the moon has done something naughty and needs to have its identity protected, but it can again be seen to have two lobes, suggesting again that it’s the result of the collision of two former moons. The two-lobed “dumb bell” appearance is quite common and approached by orbit-swapping moon pairs of moons near other planets. It’s about nineteen kilometres long and averages 57 783 kilometres from the barycentre. This figure combined with Hydra’s gives some indication of how close together the outer moons are, as these are the two outermost and there’s a highly unstable region close to Pluto-Charon, so there isn’t much space between them for moons to exist. Kerberos was named after an online poll and was not the most popular choice, and it’s spelt that way because there’s already an asteroid called Cerberus. The final choice was made by the IAU. Hmmm.

The next moon in, Nix, also has a story behind its name, which has again been re-spelt. Nyx is the Greek goddess of night, but since there was already an asteroid with that name, it became Nix in Pluto’s case, which is the Coptic spelling: “Ⲛⲓⲝ”. There’s actually a pretty good image of Nix from New Horizons:

To me, the brown smudge closest to the camera, which is eighteen kilometres across, looks like tholins, and there are also white bits which I imagine are water ice. Nix is almost exactly fifty kilometres long. Like all the smaller moons, Nix doesn’t have captured rotation but tumbles, so all these four moons have no north or south in the rotational sense.

The innermost small Plutonian moon is Styx, and if you thought Kerberos had a poor image, just look at this:

It can be conjectured to be elongated like Nix and is the dimmest known object in the Solar System at a magnitude of 27. That is, it’s as dim compared to a star like Vega as Vega itself is to the Sun, from Earth of course. I’m a little surprised by this because I would’ve thought Adonis, for example, would be dimmer, since that asteroid is only two hundred metres across, but that’s actually hundreds of times brighter at 18. Styx is a sensible name because crossing its orbit brings one into Pluto’s kingdom, more or less, and it’s also the next moon out from Charon. Styx’s longest dimension is sixteen kilometres, so it’s smaller than the oft-employed Isle Of Wight yardstick. It takes twenty days to orbit the barycentre, 42 656 kilometres away.

All of the outer moons have orbital resonances with each other. Styx is almost in harmony with Pluto-Charon too. This brings up the question of their probable mode of formation. All are grey, unlike Pluto, and are thought to have been formed in a similar manner to Cynthia, with an impact from a large body kicking up débris from the surface which later fell into orbits and coalesced. These orbits would’ve been closer to Pluto than they currently are. Interestingly, three of the moons were named in 1940 in a SF story by Peter Hamilton: Cerberus (sic), Charon and Styx. Their orbits are fairly chaotic and not fixed over millions of years.

Next time I’ll turn to the other largish worlds beyond Neptune. We’re really approaching the end now. Thank you for your patience.

Hail Eris!

It used to be so simple, concordant and ordered. There were nine planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Hamlet, Neptune and Pluto. Of course, on the whole people didn’t call the one between Saturn and Neptune by that name but my patience with puerile jokes is finite and I actually think making one of them a joke just because it has a ridiculous name does it and science a disservice. My Very Eager Mother Just Served Us Nine Pizzas. Many Volcanoes Erupt Mulberry Jam Sandwiches Under Normal Pressure, which is the one I remember. Those mnemonics are actually quite odd, not just because they’re memorable sentences – it’d be odd for a mnemonic not to be memorable – but because I don’t actually think many people have any problem remembering what order the planets are in. It’s a bit like “Richard Of York Gave Battle In Vain” or “Roy G. Biv”. It isn’t really hard to remember what order the colours of the rainbow are because they blend into each other: orange is reddish yellow, indigo bluish violet and so on. Indigo in fact is just a kludge so they add up to seven. It’s not that it isn’t a real spectral colour so much as that lime green and cyan are too, but don’t get a mention.

I have a dormant project on the Althist Wiki called ‘The Caroline Era‘, where I imagined that instead of history doing a seemingly weird swerve at the end of the 1970s CE, it just carried on going in the same direction, with the post-war consensus being preserved. It turns out to be messy and difficult to contrive circumstances in which this could’ve happened. No fewer than seven major trends would have to have been different beforehand in order for this to have continued, one of which occurred as early as 1820. This alternate history also has different astronomy, not because there’s any difference in the planets, moons and the like but because the attitudes towards them were preserved and the technology available for investigating them advanced more slowly, in a way. Two of the ways in which this manifests itself are in the names of the solar planets and what’s considered a planet.

Back in the day, a planet was considered a large round non-luminous object orbiting the Sun independently, more or less. There wasn’t a firm definition but this is probably what people would agree with if you described them that way. I have already gone over the rather dubious procedures which led to this being changed to something most ordinary people would disagree with. Before this happened, however, astronomers, science fiction writers and others practically had a name picked out ready to apply to the next major planet to be discovered: Persephone. Persephone is kind of supposed to be the name of the planet, except that there’s a long-established asteroid called Persephone too. That said, there are also many duplicate names in the system and it doesn’t seem to have stopped astronomers reusing them. Ganymede springs to mind. Also, there’s a Latin version, Proserpina, which is also an asteroid, discovered quite early. Nonetheless the opinion is expressed that any “proper” planet out there beyond Pluto will not be called Persephone for this reason.

When Eris was discovered, it wasn’t given a name because its discovery was the main cause of controversy over the definition of a planet, which I’ve already said I consider rather silly. Because it wasn’t clear how it should be regarded, and there are different naming conventions for differently-classified objects in the system, it couldn’t be officially named. It was, though, given the unofficial name Xena after a show I’ve never seen called ‘Xena, Warrior Princess’, and its moon was given the name Dysnomia. The problem Eris was seen to pose was that if it were to be admitted into official planetaricity, the chances are that a lot of other similar worlds would also have to be called planets, and we could well have ended up with more than a hundred official planets. Now I have to admit that one of the things which annoyed me about what I now think of as the children’s space horror book ‘Galactic Aliens‘ (my review is on that page) was its portrayal of star systems as containing dozens of planets, which seemed unrealistic to me, but it now appears that it’s merely a question of definition, and the slight sense of disease I feel at this is not widely shared. The IAU decided to redefine “planet” because of Eris, making its name, after the goddess of discord, highly appropriate because that proved to be unpopular with the public. I presume the motive for calling it that was its disruption of the concept of “planet”, and it certainly succeeded in sowing discord when it provoked the turn against Pluto’s planethood among IAU members.

Eris is comparable in size and mass to Pluto and the probable former plutino Triton. Eris is a mere two percent smaller than Pluto in diameter and 27% more massive, which kind of makes the two cross over and means there isn’t much to choose between them. Hence there is a sense of fairness in excluding Pluto as a planet if Eris isn’t alowed to be one either. Nonetheless, if it had been discovered under different circumstances it would almost certainly have been thought of as one. There is no reason why, if you look at Pluto as a planet, as we did for many decades, you shouldn’t also look at Eris as one.

Compare and contrast this with Sedna. Not to diss the world, but it’s only a little larger than Ceres. Its mass is unknown because it seems to have no moon, which is unusual for these objects. It counts as a dwarf planet, to be sure, but Pluto and Eris are on a different scale.

Naturally Eris has never been visited. It’s the seventeenth largest world in the system, and the largest never to have had a spacecraft sent to it or past it. It averages almost 68 AU from the Sun, takes 559 years to orbit and is currently about a hundred AU from us. Sunlight takes thirteen hours to get there right now. At its closest approach, it comes slightly closer than Pluto’s average distance but it doesn’t cross Neptune’s orbit and is therefore not a plutino and doesn’t interact with Neptune. Its maximum distance from the Sun is 97.4 AU, which means it’s currently about as far away as it gets. I suspect that there are a number of Kuiper belt objects whose existence we only know of because they’re currently near perihelion, but this doesn’t apply to Eris. The Sun is currently over nine thousand times dimmer there than it is here. The distance of the world, and in fact I’m going to call a spade a spade and refer to it as a planet, the planet from the Sun is unprecedented in this series. It’s about five dozen times as bright as moonlight at that distance, meaning that finally the idea of a distant planet being so far from the Sun that it’s like night there may finally have begun to be fairly accurate, although a night of a brightness only seen on this planet had there been a fairly nearby supernova in the past few days. Surface temperatures vary between -243 and -217°C, so it doesn’t even get warm enough there to melt nitrogen or oxygen. It’s currently on the low side, and the seasons would be quite substantially determined by its distance from the Sun rather than just its axial tilt, although that’s also considerable at 78° if Dysnomia’s orbit is anything to go by.

Eris is bright. It isn’t like many of the other trans-Neptunian objects (TNOs), which are quite dark and also red. Its surface reflects most of the light back again, which makes it colder than other such worlds at comparable distances, and it’s also unlike Pluto, Charon and Triton in that respect. This is Charon:

. . .which looks quite like Pluto:

(to an extent), which in turn resembles Triton to a certain degree:

All three worlds have tholins on their surfaces to some extent and reflect up to 76% of sunlight. Eris could well be as bright as Enceladus. Something else is going on, or has gone on, there. One thing which very probably does happen is that it has a seasonal atmosphere. The surface is likely to be covered in a layer of frozen nitrogen and methane which will evaporate in a couple of centuries time when spring comes, at which point it will have a tenuous nitrogen-methane atmosphere for the summer, then with the onset of autumn this will freeze and snow onto the surface, once again covering it. This is a five and a half century process though, so we will never witness it. The last time Eris was where it is now was two decades before the Battle of Bosworth Field and three decades before Columbus reached the New World, and each season lasts something like the interval between the first Boer War and the present day, which means it’s just barely within the memory of my grandparents, and I’m middle-aged. That would be the average length. In reality, the winter is the longest season and the summer the shortest, and all seasons are somewhat affected by the considerable axial tilt. My ignorance of calculus makes it impossible to be more precise.

In considering Eris, we’re thrown back substantially onto pre-space age technology. Although there have been many advances in astronomical observation and reasoning since 1957, considering the planet is reminiscent of the kind of observation and reasoning astronomers used to have to use when all they had was what they saw through telescopes. This is not entirely true though, because conclusions were drawn on the basis of the actual space exploration of similar worlds, which didn’t just rely on light and other electromagnetic radiation, and the Hubble Space Telescope made a big difference too. There are also better modelling techniques. Even so, Eris is a dot in a telescope with another dot, Dysnomia, orbiting it, and astronomers have to base most of their studies on those. I’m once again reminded of Chesley Bonestell’s paintings of Saturn seen from different moons where the central subject more or less had to be the planet’s rather than the moons’ appearance because little was known about the characteristics of the moons themselves other than what was implied by their appearance through a less-than-ideal set of telescopes through Earth’s atmosphere, and their movements. Io, for example, was probably never depicted with a volcanic eruption taking place on it until the late ’70s or after. Nonetheless it’s still possible to go a long way with what we’ve got, and there’s even a kind of nostalgia to it. Just as we used to imagine oceans on Venus and canals on Mars, so we can project our wishes onto Eris. For instance, it could have the ruins of ancient alien space bases on it and we’d be none the wiser, although I very much doubt that’s so. Science fiction might be able to colour it in that way, but the genre hasn’t really developed in that direction. The planet is in a bit of a peculiar position because on the one hand it was fêted and imagined in detail for decades before it was discovered – mentioned on classic ‘Doctor Who’ for example – but when it was discovered for real, it ceased to be considered a planet within about a year and the kind of popular culture which existed by then had little space for such a concept as the “tenth” planet. It’s also been stated that not calling it the tenth planet is insulting to Clive Tombaugh’s memory, because he discovered Pluto. Calling it the ninth would be the same, and also wouldn’t make any sense. It’s either the tenth planet or not a planet at all.

The presence of Dysnomia is fairly typical for dwarf planets, which are often binary or at least have moons. Dysnomia is around seven hundred kilometres in diameter and is therefore almost certainly spheroidal. Here’s an image of the two together:

Eris is the brighter light in the middle, Dysomia the left lesser light. Since the moon can be observed to orbit Eris and perhaps also displace it as it does so, the time taken and the distance between the two can be used to calculate the mass of Eris, and the displacement would enable the density and mass of Dysnomia to be found. The moon might be a rubble pile, apparently, which surprises me because it seems too large not to have welded itself together. It was originally unofficially called Gabrielle due to the ‘Xena, Warrior Princess’ thing. Dysnomia orbits Eris once in almost sixteen days, averaging 37 000 kilometres separation in an almost circular path. It’s a lot less reflective, so it may not be made of the same stuff.

It’s possible to say a few of the usual things about Eris which follow from its known size, mass, density and orbit. It has a diameter of 2326 kilometres and a surface gravity 8.4% of Earth’s, which is about half Cynthia’s and close to Pluto’s. Its orbit is inclined 44° to the ecliptic. Its gleaming surface, which is almost uniformly bright, makes it difficult to measure its rotation, but it seems to be fourteen and a half days, making it just a little less than the “month” of Dysnomia. The planet is actually easily spottable through a large telescope. It wasn’t discovered before because its high orbital tilt keeps it away from the ecliptic where other planets generally stay. Even so, right now it is about ten thousand times too dim to be seen with the unaided naked eye, which is about as bright as a Sun-like star would look at the edge of our Galaxy, i.e. about twenty thousand light years away, so it ain’t exactly bright from this distance. It spends about thirty years in each of the maybe four zodiacal constellations it passes through and is currently in Cetus, the Whale.

Eris is not a plutino but a scattered disc object. The scattered disc is not the Kuiper belt, which consists of objects orbiting close to the plane of the Solar System, but comprises objects with highly tilted orbits such as Eris itself and many others, whereas the Kuiper belt planetoids orbit close to the plane of the inner system. The planet, however, still is quite remarkable as it shines forth compared to many of the others in the scattered disc, which have probably yet to be discovered due to their low albedo. It’s a little hard to imagine what could be so exceptional of Eris, it being, like the others, remote from other such objects barring its moon, and other scattered disc objects also have moons, often large compared to their own bulk like Dysnomia. However, discussion of this should wait for another time when I’ll be going into trans-Neptunian objects in more depth.

The surface area is almost seventeen million square kilometres, which is larger than any continent except Eurasia. It has a 26-hour day. It’s higher in rock than many other outer worlds. There’s very little else to say about Eris because so little is known about it, but it’s certainly a fair target for exploration as it’s certainly unusual. The problem is that because the charisma of being declared a planet was denied it, it’s harder to make a case for visiting it. Pluto didn’t suffer this problem because New Horizons was launched a few months before it lost its status. With current spaceflight technology, it would take a spacecraft nearly a quarter of a century to reach it, and once there it would take a radio signal more than half a day to reach Earth at its current distance. It won’t reach its closest approach until the late twenty-third century. The only probe-based exploration undertaken was from New Horizons itself, which was actually further from Eris than Earth was at the time, the advantage being that it was seen from a different angle.

To be honest, it’s a tall order to try to say anything much at all about Eris, as you may have gathered, but there would surely be a lot to say if the opportunity arose to explore it. Right now this seems quite unlikely, and by the time it’s in a position to be visited, we’ll probably be extinct or have lost the ability to launch spacecraft, so don’t hold your breath.

Next time, I’ll be talking about Pluto’s moons, of which there are five known.

Neptune’s Smaller Moons

For Neptune, or rather knowledge thereof, the early 1970s CE were a simpler time. In fact any time between 1949 and 1989 was a simpler time. Back then, Kuiper having discovered Nereid, a smaller and peculiar moon, at the end of the ’40s, Neptune only seemed to have two moons: Triton and Nereid. This state of affairs continued until the end of the ’80s, which was approximately one Neptunian season. Four decades during which the planet only appeared to have two moons. I’ll start with that.

I’ve already mentioned Triton, the oddball moon of the Neptunian system two hundred times as massive as all its other moons put together, orbiting backwards and at an angle, in an almost perfectly circular trajectory. I haven’t mentioned the equally oddball second moon discovered, Nereid, and I say the early ’70s were a simpler time but in fact its own orbit is very peculiar. Nereid has the most eccentric known orbit of any moon. It sometimes feels like discussing the orbit of a celestial body is a bit tangential to the core of its nature, but orbits have important consequences for the nature of planets, moons and their neighbours, and in this case it’s so odd that it would be strange not to mention it, particularly back in 1971 when that was practically all that was known about it. It sometimes feels like the Solar System “frays at the edges” with all this stuff, because things out here are really quite outré compared to the relatively regular innards of this system we call solar. Nereid’s orbit is entirely outside Triton’s, approaching Neptune by 1 353 600 kilometres at its closest and moving out to a maximum of 9 623 700 kilometres distance from the planet. It takes five days less than a year to go all the way round, which is appealingly similar to Earth’s sidereal period. In fact of all Solar System objects its year seems closest to ours. No other moon is remotely as eccentric. At its closest, Neptune would be a little larger than the Sun is in our own sky, and at its furthest, six months later (so to speak), about the size of a lentil on one’s dinner plate. This is probably the result of Triton’s capture, which to me suggests there are other former moons wandering far beyond Pluto or even in interstellar space, or maybe in the “Gap“.

Nereid is small and grey. There is no good image. The best one is this:

Not very impressive, eh?

Unlike Triton, Nereid orbits in the usual direction, as do two other irregular moons Sao and Laomedea, further out. Another moon, Helimede, is a remarkably similar colour but orbits the other way. It’s considered to be a bit that chipped off of Nereid. Nereid itself is about 360 kilometres across on average and may be somewhat spherical but by no means perfectly so. It’s one of several bodies in the system which are right on the border of being round, and is almost as large as the definitely round (sans Herschel) Mimas, but also rather denser. Its shape is therefore hard to determine. Certainly its gravity would be sufficient to pull Mimas-like material into a spheroid, since it’s higher, but that very density may result in the moon being tougher and more able to support its own weight without collapsing. However, its variation in brightness probably means it’s quite irregular in shape and closer to Hyperion in form. Its colour is markèdly unlike that of most centaurs, and it’s therefore probably a “native” Neptunian moon. There’s water ice on its surface.

Proteus is the one which really surprised me. On the whole, the Voyager probes and others only discovered small moons, although Charles Kowal’s discovery of Leda skews that for the Jovian satellites because it’s unusually small for a telescopic discovery of that time. Proteus is actually the second largest Neptunian moon, being somewhat larger than Nereid, and is shown at the top of this post. It orbits the planet at 117 647 kilometres from the barycentre on average in a fairly round orbit, though nowhere near as round as Triton’s. It can be determined not to be perfectly spherical and is in fact not even particularly rounded, with dimensions of 424 x 390 x 396 kilometres. Its surface consists of a number of planes (or plains) with sharp angles between them at their edges and it’s uniform in colour, being somewhat reddish like many other outer system worlds. It was discovered by Voyager, but two months before the space probe got to Neptune.

Unlike Nereid, Proteus was close enough to Voyager 2 to be mapped. As can be seen above, it’s heavily cratered and its surface is therefore likely to be quite old, meaning that nothing much has happened to it in a long time. NASA also had a very steep “learning curve” with Proteus compared to Nereid as it went from being unknown to being mapped within a few weeks, whereas Nereid’s existence has been established for six dozen years now and still there is no map available except possibly the kind of vague albedo feature map which used to be done for Pluto before a spacecraft got there. It can also be seen through the Hubble Space Telescope. It’s fairly dark, probably because its surface consists of hydrocarbons and cyanides. The only named feature on its surface is the relatively large crater Pharos, 260 kilometres across, but due to its somewhat irregular shape this fails to give it the “Death Star” appearance Mimas has. Proteus is also receding from Neptune due to tidal forces and is now eight thousand kilometres further from it than when it first formed. Unsurprisingly, given that it was undiscovered for so long, it’s a lot darker than Nereid.

The inner moons generally are coated in the same material as Proteus. A couple of them are quite notable. For instance, Larissa, which is 194 kilometres in diameter, was accidentally observed passing in front of a star in 1981, leading to the correct but unwarranted conclusion that Neptune has rings. The chances of a moon of that size being seen to cover a star are very small just anyway, but in Neptune’s case it’s even less likely because it moves against the “fixed” stars so slowly, taking almost three months to cover a distance equivalent to the face of the Sun. Larissa’s period is about twelve hours and it orbits only 73 400 kilometres above the centre of Neptune, putting it close to the Roche Limit, where large bodies are torn apart by gravity. It was, however, given a provisional designation in ’81, namely S/1981 N1, so it was accepted as a moon back then. Like the other inner satellites, it’s likely to be a rubble pile, without enough gravity to pull itself together as a solid object. It may be a future ring.

Another somewhat interesting moon is Hippocamp, which is so dim Voyager failed to notice it and had to wait for the Hubble Space Telescope to discover it, which was done by the combination of a number of images as even then it was too faint to be spotted. It seems to reflect less than ten percent of the light falling on it. It’s only seventeen kilometres across.

The closest moon to Neptune, and in fact to any solar gas giant at all, is Naiad, taking only seven hours to travel round the planet. It’s quite elongated at eight by five dozen kilometres, and will either become a ring or fall into the atmosphere in the relatively near future. Thalassa, the next moon out, is coörbital with it. Their orbits are only eighteen hundred kilometres apart but they never approach that closely because they move north and south of each other as they orbit, putting them a minimum of 2 800 kilometres apart. It’s about the planet’s radius from the cloud tops, making Neptune occupy most of its sky. This would make the surface look deep purple if it has a reddish coating like the others.

Like some other moons, the naming scheme has the prograde moons end in A, the retrograde in E and the highly tilted in O. The two outermost moons, Psamathe and Neso, are relatively close to each other, and stand in contrast to Naiad by being the most distant moons of any known planet at forty-six and fifty million kilometres. Neptune’s lower mass also gives them exceedingly long years of around a quarter of a century.

That’s it for Neptune and its moons, and I’ve already done Pluto, so next stop Eris.

Triton

Triton, along with the similarly-named Titan and also Ganymede, is one of the largest moons of the outer system. Before Voyager 2 reached it, it was considered possibly the largest moon of all. Moreover, apart from our own highly anomalous Cynthia, it’s large in proportion to its planet’s size. Using the largest moons of each planet, the proportions of their masses work out thus:

Earth:Cynthia – 81
Jupiter:Ganymede – 12 808
Saturn:Titan – 4 222
Hamlet:Titania – 25 294
Neptune:Triton – 4 768

In terms of equatorial diameter, the ratios work out thus:

Earth:Cynthia – 3.67
Jupiter:Ganymede – 26.54
Saturn:Titan – 22.62
Hamlet:Titania – 32.15
Neptune:Triton – 18.19

Just for reference, the ratios for Pluto:Charon are 1.96 for diameter and 8.22 for mass, but Pluto‘s status as a planet is not unquestioned. It can in any case be seen that of all the large moons, Neptune’s Triton is still in proportion and there’s a big gap before our own special case, but it is still unusually big.

A common mechanism for the formation of moons is for the region around a planet to behave like the solar nebula did when the planets themselves were formed, with eddies in the cloud pulling in matter as the planet takes shape. Hamlet’s moons may be an exception to this, as they may result from the trauma that planet underwent. Outer and irregular moons are, however, often the result of captures and this is particularly evident when they orbit the opposite way from most Solar System bodies, and Triton is by far the largest body to do this. This has been known since its orbit was plotted in the nineteenth century. Due to its size and therefore relative brightness, the moon also holds the record for the shortest gap between the discovery of its planet and its own, as it was found in October 1846 CE, only a month after Neptune. This, however, is not as impressive as it sounds because all the planets out to Saturn have been known since ancient times and Pluto is very small and may not be counted as a planet, so it basically means that of the two planets discovered in the telescopic age, one of them has a very large and relatively bright moon which was easy to spot.

Certainly by the ’70s, Triton was, as it still is, considered to be a captured planet, though that would probably generally be qualified as “dwarf” now. Given the controversy of what counts as a planet, Triton of all worlds in the system has surely got to be the closest to that definition, as although it may have undergone the mishap, if that’s an appropriate word, of being grabbed by Neptune, it’s quite large and massive and probably used to dominate its orbit, as the 2006 IAU definition demands. Strictly speaking, and perhaps by being a bit arsy, Earth doesn’t even count as a planet by that definition. Hear ye then: Triton is a planet. I was first introduced to this piece of information in the ’70s, which is how I can make that provisional estimate of its timing, and consequently looked forward to the Voyager missions as including an encounter with a body likely to be very like Pluto. At the time there was little prospect of a mission to that planet, so it was the best I felt I could hope for.

The Voyagers took advantage of a rare planetary alignment which only occurs once every two centuries and started in 1976, dubbed the “Grand Tour”, which would allow probes to visit several planets in a row. This idea dates from at the latest 1971, and there were initially three possibilities. Two involved Jupiter, Saturn and Pluto and the other all the gas giants, but it was impossible to visit both them and Pluto on the same mission, at least efficiently enough to be practical. The ultimate decision was to take the last option, although Voyager 1 is a bit like the first two with the omission of Pluto. Also, although the Voyager 2 mission resembles the final option quite closely, it isn’t actually the same as the initial plan, which involved launching in 1979, visiting Jupiter and Saturn in ’81 and ’82 respectively, Hamlet in ’86 and Neptune in ’88, as the Voyagers were launched in ’77. The earliest option for Pluto inolved a ’76 launch, visits to the two inner gas giants in ’78 and ’79 respectively and Pluto in ’85. Although the final choice was, I think, a good one, it’s interesting to contemplate what might have been. It would be disappointing not to have visited the ice giants but amazing to have got to Pluto so early, and it also seems very likely that if that had happened, Pluto would never have been demoted. However, it was not to be, and this makes Triton a kind of Pluto substitute. It is in fact very likely to be similar to Pluto and it’s worth comparing the two.

Excluding the Sun, Triton is the fifteenth largest body in the system, Pluto the sixteenth. Eris is next on the list, incidentally. In terms of mass, Eris is between Pluto and the more massive Triton. Circling Neptune, Triton takes 165 years to orbit the Sun , Pluto 248, which is close to a 3:2 ratio (lots of ratios in this post for some reason) like the other plutinos. Considering its similarity, it seems likely that Triton was itself a plutino with a 248-year period like Pluto’s (which is what defines them), and right now I’m also wondering whether some of the other moons of Neptune, particularly Nereid with its peculiar orbit, were in fact originally moons of Triton. I expect this has already been researched.

Being retrograde is not the only peculiar feature of Triton’s orbit. It also varies its tilt through a cycle corresponding to only four Neptunian years, and is moreover remarkably round, by contrast with Nereid’s. Its distance from the barycentre (centre of gravity between two bodies) varies by less than six kilometres each way. This may be the roundest orbit in the Solar System and is quite remarkable. Our own orbital eccentricity is a thousand times greater. Hence there are a few combined mysteries here, which are probably related: the moon orbits backwards, shifts rapidly (over a period of about five centuries) in how tilted its orbit is and hardly varies at all from its mean distance of 354 759 kilometres from the barycentre, which is around seventy-five kilometres from the centre of Neptune. The size of the orbit is also only a little less than Cynthia’s around Earth. I have an illustration by Luděk Pešek of the moon in Neptune’s sky, painted in the early ’70s, and at the time it was considered much larger than Cynthia. It’s now been found to be somewhat smaller at 2706 kilometres diameter, and is of course somewhat less dense due to its ice content, although Cynthia, being formed from the Earth’s outer and lighter layers, is only about 50% denser. That said, Triton still averages over twice the density of water, making it one of the densest objects in the system beyond the orbit of Jupiter, and also denser than Pluto. Given the nature of its surface, this is all the more remarkable, and I’ll come to that.

Before its capture, Triton would’ve dominated its region of the system beyond Neptune, and perhaps even have counted as a planet in its own right by the IAU 2006 definition. Neptune is in a peculiar position regarding the Bone-Titius Series, and if that is in fact a law of nature it could be expected to have been somewhere else in the past. This would presumably in turn have meant that the plutinos have fallen into orbital resonance with it since it moved and the presence of small, solid planets beyond its orbit would lend the Solar System a pleasing symmetry, with small rocky planets in the inner system, gas giants in the middle and a further succession of small icy planets beyond them. It is of course highly speculative to suggest that Neptune used to be somewhere else. Olaf Stapledon supposed Neptune to be followed by a further three planets, of which Pluto was extremely dense and made of iron, because only with such a hefty planet would be able to perturb Neptune to the extent it is. It was common at the time for scientists to presume this as they’d predicted Pluto’s existence from these perturbations, but I’ve gone on about this elsewhere.

Pluto and Triton are almost the same in composition, suggesting a common origin. The moon’s surface, however, is somewhat different. It’s unusually flat, with variations in elevation of less than a kilometre. It also has a surprising composition: it’s made of frozen nitrogen. At this distance from the Sun, the gas which makes up most of our atmosphere composes the solid, though also soft, surface of a world. It’s therefore no surprise that the surface temperature is exceedingly low at -235°C. However, there is also a greenhouse effect, in this case considerably more literal than usual. The nitrogen forms a clear surface which traps the sunlight just below it, heating the subterranean nitrogen and causing it to erupt out of the surface like geysers or volcanoes to a height of around eight kilometres. This then drifts downwind by as much as a hundred kilometres, leaving streaks on the landscape. This process also maintains the moon’s nitrogen atmosphere, which is thin by terrestrial standards but not as tenuous as many of the atmospheres of other moons, at fourteen microbars. Although this may not sound like much, it’s enough to be a collisional atmosphere. That is, the molecules in Triton’s atmosphere are near enough to one another to come in contact at least occasionally, which means the air behaves as a fluid like air at sea level on Earth, rather than just bouncing around or orbiting the moon as it does on our own. Even so, Triton’s atmosphere is a lot thinner than expected. The lower the temperature, the easier it is for a body to hold on to gases and perhaps liquids if the atmospheric pressure supports them. Nonetheless, Triton doesn’t seem to be very good at it. Its surface gravity is 0.0794 that of ours, over half that of Titan, whose atmosphere is several times denser than Earth’s and whose temperature is something like two and a half times higher. There’s a small amount of methane in the atmosphere too, making it like a much thinner version of Titan’s, but also colder since it’s below both substance’s freezing points. Just as an aside, it’s been conjectured that of all the substances likely to form oceans on planets or moons somewhat similar to Earth, i.e. oceans on the surface along with land masses or islands, nitrogen would actually be the most common liquid of all, with water only coming in second. Triton is not a world with permanent bodies of liquid on its surface, but like Cynthia, it does have large flat plains of solidified “lava”, in this case frozen nitrogen, which contributes to its general flatness. Unlike water, most liquids freeze “under” rather than “over”, so the frozen nitrogen lava plains of Triton would have done so by cooling on the surface and then precipitating down inside the body of liquid, gradually filling up until the whole lake or sea was frozen solid, except that it would then have melted and vaporised in some places and pushed through once again. The geysers are near the south pole, similar to the Enceladus situation, but this is a much larger and heavier world than that moon. However, there are also claims that the lava is in fact an ammonia-water mixture, so all of this is provisional. The fact remains that most of the atmosphere is nitrogen.

The resolution of the picture at the top of this post is surprisingly large considering it’s a mosaic of images captured by a camera from the mid-’70s. Although it’s diminutive on this page,clicking on it will show it in its full glory. Pixels are only five hundred metres across at the centre, so this is a pretty detailed map of most of the surface and would show medium-sized parks if it were a picture of Earth. It’s like a photo of Earth from the ISS, although of course the whole of our planet wouldn’t be visible from such a distance. A distinctive feature is the so-called “canteloupe terrain” because it looks a bit like this kind of melon:

Triton’s version looks like this:

The winding heights are several hundred metres high and a few hundred kilometres across, and the plains they surround are safely two hundred kilometres wide, which is significant for a moon which, though large, is only about ten times that in diameter. The ridges consist of water ice which has been squeezed upward, and the whole surface of the moon is quite young as it has few craters. It could even be Cenozoic. This is possibly a surface which didn’t exist when T. rex walked the earth, although another surface did. To my mind, this raises the question of whether Triton was actually an independent planet at the time and if this melting can be blamed on the capture.

The similarity of the smooth basins to lunar maria will not have escaped you. The difference is that whereas those are made of basalt, these are nitrogen, as I’ve said. It’s worth bringing up again though, because on different worlds at different temperatures the same kinds of processes and structures exist but are made of different substances. On the whole, most substances which can be solid, liquid or gaseous in a given situation without major changes are, unsurprisingly, broadly subject to the same kinds of physical laws. The exception, more surprisingly, is water, because in the state with which we’re familiar, that is, under enough pressure to give it a liquid phase but only enough to ensure it has the most loosely spaced solid one, it expands and therefore floats when it freezes. This would have consequences such as the canteloupe terrain on Triton, which could be caused by its expansion as it solidified. Ironically, liquid nitrogen and molten rock (a bit of a generalisation) have things in common which they don’t share with water, a highly anomalous substance, due to water’s expansion on cooling and surface tension, among other things.

The solid nitrogen on Triton can be seen as the slightly blue-green streak across the image at the top of this post. It’s actually β nitrogen, which forms hexagonal crystals although they don’t form arrays like graphite or honeycomb. I can’t swear to this, but since the element immediately below nitrogen in the periodic table is phosphorus, whose least derived form is the dangerous but waxy white phosphorus, and I suspect that solid nitrogen fairly close to its triple (“melting”) point is also like this. This is not a thorough scientific appraisal so much as a hunch. White phosphorus slowly combines with oxygen in Earth’s atmosphere, and nitrogen as such is highly reactive, hence its use in explosives, but generally reacts with itself to form a highly inert gas at temperatures compatible with human life. On Triton, whether or not it’s reactive it may not have much to react with and the lower temperature would inhibit many such reactions. The issue here is really that although, as I’ve said, in some circumstances it hardly matters whether the substance in question is silica or nitrogen, as both can form volcanoes, erupt, produce lava flows and the like, such a substance as solid nitrogen or a mass of liquid methane on a lake on Titan is far from our own experience and our expectations can be misleading. However, it does seem highly feasible that the plains of the canteloupe terrain and the general flatness of the landscape is due to the waxy softness of the nitrogen which forms part of them. At this temperature also, water ice is almost a normal solid, expanding with increasing temperature and contracting as it cools, but it has clearly passed through the anomalous phase we think of as normal behaviour for a liquid.

What’s Triton’s interior like? Nitrogen in this solid form is very slightly denser than water at our freezing point, so it unsurprisingly covers the surface and forms a substantial part of the crust. The moon is rockier than the other moons trans the asteroid belt with the exception of Io and Europa, which are basically just balls of rock like the inner planets with a thin coating of other substances. Triton does still have an icy mantle but it will have a rocky core high in metals like a terrestrial planet’s. The brightness of the nitrogen surface cools the moon while simultaneously heating the upper layers of the crust, making it one of the coldest worlds in the known Solar System. The geysers are driven by the heat of the Sun, such as it is, emphasising what looks to us from here, close in to the Sun, to be a thermally delicate state. It might be expected not to last long in its present form when the Sun becomes a red giant, but the same is true of Earth. Solid and liquid matter as such is not the kind of thing which can cope well with the kind of temperatures found near stars. There’s also the “logarithmic” effect of low temperatures. The freezing point of water is about half the temperature of a hot oven and its boiling point at sea level is less than twice the temperature at our South Pole in midwinter. Nitrogen and oxygen have similar melting and boiling points at the rather mind-boggling sea level atmospheric pressure, and to us the fourteen degrees of difference between the boiling and freezing points of nitrogen sounds very narrow, but if centigrade had been standardised with nitrogen instead of water, absolute zero would be -550 degrees below zero. There’s an effectively infinite range of temperature before reaching absolute zero, which is like the speed of light in that respect – effectively inaccessible and some kind of ultimate limit.

Although they have their own smaller moons, Pluto and Charon are effectively a double planet system. It’s been theorised that the same was also true of Triton before its capture. Many other Kuiper belt objects are binary, and modelling of the dynamics of capture show that Triton is more likely to survive if this was so. The other object would be ejected from the system. To my mind, this contrasts with Hamlet’s situation, where a similar collision may have resulted in the “moon”, such as it was, being incorporated with the substance of the planet itself and also disrupting its axial tilt. The question then arises of where Triton’s companion might be now if it survived the encounter, and in my current ignorance I wonder about the similarly-sized Eris.

The name Triton originates from Poseidon’s (i.e. Neptune the god’s Greek counterpart) son, and has been more widely used for other purposes than most other names of major planets and moons. For instance, this is a triton:

This is the animal that first springs to mind for me when I think of newts, but they are nonetheless known as tritons. It’s also used as the name of a sea snail and a species of cockatoo. The list is much longer than for many or most other names also used for celestial bodies, which seems rather anomalous to me and possibly reflects the relative obscurity of the moon compared to some others, though maybe I’m out of touch in saying that.

Neptune’s satellite system as a whole is sparser than the other gas giants’, with only fourteen known moons. Until the ’80s, only two were known. This may be connected to Triton’s presence, either enabling it to remain without disturbance or maybe due to its own disturbance of the system. When Triton first arrived, its surface is likely to have been molten for an æon. In Triton’s case this presumably means a liquid nitrogen ocean over a water ice bed, which makes it seem that it was captured in the late cryptozoic eon, if that estimate is at all accurate. Hence over the period when Earth was almost frozen over itself and had little or no surface liquid, Titan and Triton both had oceans, and the latter would’ve been a possible member of the very large number of worlds with liquid nitrogen bodies of liquid on their surfaces, which is plausible but unknown. It’s also unclear whether it had landmasses. But in any case, the number of moons is surprisingly small. The comparably-sized Hamlet has more than two dozen, but Neptune only has fourteen. All but two of these were unknown before Voyager. Triton’s mass is two hundred times the mass of all the other moons put together.

As a world, Triton is somewhat smaller than Cynthia. Its surface area is 23 million square kilometres, 40% of which has been imaged. This makes it bigger than any country and a little larger than North America, but smaller than Afrika or Eurasia. It seems entirely feasible, probable in fact, that its surface is covered by more nitrogen than is present in our own atmosphere. Triton and Pluto both have irregular pits with cliff edges on their surfaces which are not craters, called “cavi”. Ten of these have been named, all after water spirits. Cavi usually occur in groups. There are only nine named craters. Other features include those found elsewhere on other solid bodies in the system (and probably throughout the Universe): dorsa, sulci, catenæ (chains of craters caused by meteoroids breaking up before impact), maculæ (dark spots), pateræ (irregular craters, not the same as cavi), planitiæ and plana. There are also “regions”.

Tholins are present on Triton, where they are distinctive in containing heterocyclic nitrogen compounds. This makes them chemically similar to alkaloids, which are a family-resemblance defined class of nitrogenous compounds which tend to have rings containing nitrogen in their molecules, a markèd physiological effect on some organisms and originate in plants. However, there are animal alkaloids such as toad poisons and adrenalin, so it’s entirely feasible that there are basically drugs on Triton’s surface. Unlike Titan, there are no persistent solvents on Triton, so in a similar way to moondust being chemically different from matter in a wet or oxygen-rich environment, Tritonian tholins might be quite reactive on Earth, and might in fact be explosive. All this is my speculation, but I stand by it and feel quite confident that it would be so.

To conclude, then, probably less is known about Triton than any other body of comparable size in the system up to and including Pluto. It’s only been visited once, by Voyager 2, and was in fact the last world to be encountered by it before the “void”. Nonetheless, it’s an important world and has probably the best claim to planethood of any moon. The behaviour of objects in the outer Solar System at this point reminds me of snooker.

Next time, the other moons of Neptune, which are also interesting but even less well-known.

The Outermost Planet?

Neptune may be the outermost planet. After the torridity of having to refer to the previous planet by a silly name or bear the brunt of using an unofficial name, it’s nice to have the calm of just being able to call it “Neptune” without the irritation of puerile jokes. That said, things could’ve turned out very differently because one of the names considered for the seventh planet was actually Neptune!

The two planets are the most similar pair in the entire system. That said, having fixated on Hamlet for so long, right now the two don’t look that alike to me. Neptune has no obvious rings, spins more upright and is a much clearer and more vivid (livid?) blue than the hazy and almost featureless Hamlet. The further out a gas giant is, the more likely it is, even if bigger than Jupiter, to look like Neptune. If Tyche exists, it will be blue, and outer planets in other star systems whose stars provide less radiation than about a thousandth of solar intensity at our distance from it are also probably going to look like this, although much dimmer. The above image is actually more colourful than it would look to the unaided human eye, at least at first. At Neptune’s distance, the Sun is nearly a thousand times dimmer than at Earth’s. The logarithmic nature of senses means that this wouldn’t seem as dim as that suggests. It’s still about 360 times brighter than Cynthia ever gets. Moonlight is insufficient to make out colour, but I don’t know about sunlight on Neptune. In a way it’s odd even to consider what colour Neptune would look like to human vision as nobody will ever see it in person and it would appear to be coloured to some species who live on this planet, particularly nocturnal ones.

The Titius-Bode series does not apply to Neptune. It’s actually 30.1 AU from the Sun rather than the predicted 38.8, although Pluto is much closer to that distance. That doesn’t mean Pluto is or isn’t a planet by the way, but that astronomers expected there to be one there and therefore called it one. What’s actually happening there is quite interesting, but I’ll leave that for now. Neptune was discovered in 1846, by which time a large number of asteroids had also been found and Ceres was no longer considered a planet, which led to the idea that Bode’s Law was mere coincidence. The revision which was able to include Hamlet’s major satellites could be seen, again, as a form of pareidolia, where an increasingly vague formula is used to fit observed phenomena which actually doesn’t reflect any real process or effect but just corresponds to the various coincidences. The sequence was originally n+4, with n=0 for Mercury, rather than a simple doubling sequence, and the fact that the asteroid belt intervenes and Neptune doesn’t fit makes the idea that it’s an actual law more doubtful because there are then three out of ten exceptions to the rule. A side issue, probably not important, is the surprising convenience of Earth being at a round ten units from the Sun. The question arises, then, of whether there really is something about Neptune which puts it in the “wrong” place or whether it’s just that the spurious correlation was revealed by it. Most astronomers would agree with the latter possibility.

Neptune is not the coldest planet in the system in spite of being further from the Sun than any other known planet, at least consistently. This is because, unlike the seventh planet, it has a significant internal heat source. It takes 165 years to orbit the Sun, and having a moderate axial tilt this gives the temperate regions four-decade-long seasons. The axial tilt is 28° and the day lasts sixteen hours, which is technically close to Hamlet’s but differs in that the poles don’t spend most of their time pointing towards or away from the Sun. It might therefore be expected to have seasons dominated by the Sun, but this isn’t obvious because unlike its twin, Neptune is heated internally. This leads to Neptune being warmer than the other ice giant at cloud top level. Like the other outer planets, this heat is due to contraction of the planet from the part of the solar nebula it formed from, but in Neptune’s case there may be an extra factor in the form of its large moon Triton’s tidal influence. The centre is at around 7000°C compared to the other giant’s 5000, possibly because Neptune wasn’t disrupted, but it could also be that both planets go through warmer and colder phases and we happen to be living at a time when it’s that way round. I don’t actually know how they arrived at these figures considering that there are theories that the clouds are cold due to insulating convection layers, meaning that heat doesn’t leak out and is therefore presumably undetectable, but this is what they say. Neptune’s centre is therefore hotter than the surface of the Sun.

Regardless of the temperature at the core, the cloud tops are still very cold at around -200°C. Before Voyager 2 got there, it was speculated that the low temperature could give rise to fast winds in the atmosphere because the vibration of gas molecules at higher temperatures was absent, leading to a low-friction environment, and this did in fact turn out to be so. The winds are the fastest recorded in the system at over 2000 kph. At the equator, the average wind speed is around 1100 kph, which is about the same as the speed of sound at sea level on Earth. On Earth, the Coriolis Effect is somewhat significant in generating wind but the main driver is the primary or secondary solar heating and cooling. The Sun heats the air on this planet, causing it to expand, or cooler areas have contracting air over them, allowing the warmer air to move in and occupy the space due to the pressure difference, or in a more complicated process, land and water change temperature at different rates, causing air movement. Although the core of Neptune is far hotter than its exterior, this doesn’t seem to drive the extreme high velocity winds near the cloud tops. My guess is that it’s somewhat similar to a perpetual motion machine, which of course cannot exist. The input from whatever source to the weather systems, such as the Coriolis Effect, tidal forces and the hot interior of the planet, puts the atmosphere in motion and due to the lack of friction that energy is only lost very slowly, and consequently the winds accelerate until they reach the speed of sound, which prevents them from moving any faster. This is not a detailed explanation and may well be completely incorrect. It’s just a guess.

Neptune has more visible banding than the other ice giant, and also has rotating storms in its atmosphere which have been observed to last up to six years. This is far less durable than Jupiter’s storms, but the size and energy input are smaller so this might be expected. Neptune’s Great Dark Spot is visible in the lower part of the picture at the start of this post, but here it is again:

The spot was 13 000 kilometres long by 6 000 wide, and is a hole in the cloud deck. The white clouds around it are cirrus made of frozen methane and were instrumental in enabling the wind speed to be measured. It’s thought that the spots disappear as they approach the equator, which can take years. As I may have mentioned before, the Great Dark Spot was at the same latitude as Jupiter’s Great Red Spot, and this suggests it’s recurrent. If it is, it also shares with the GRS a tendency to appear and disappear. I’ve mentioned elsewhere that it seems to be more than coincidence that planets tend to have a fluid-related feature at this latitude, including Hawaiʻi, Olympus Mons, the Great Red Spot and this storm, which is intermittent, and although I have a vague impression of a pyramid superimposed on the bodies in question with the apex at one pole, I can’t put my finger on why this would happen or whether it actually is more than cherrypicking.

Neptune’s blueness can’t be explained simply through Rayleigh scattering and there must actually be something blue in its atmosphere which isn’t in Hamlet’s, but what this is exactly is another question entirely. Even so, it is true that the methane contributes by absorbing red light. The different hydrocarbon content contributes to it being warmer than Hamlet due to a greenhouse effect, although this is only relative as it’s still at the temperature of liquid nitrogen on Earth.

This is a fairly well-known image of clouds on Neptune above the more generally blue cloud deck. These clouds are frozen methane, but the picture also seems to show that not far below them is a blue haze with a definite level top to it. The clouds are about fifty kilometres above the haze and are casting such definite shadows because the Sun is low in the sky at this point, as evinced by the night on the right hand side of the image. Although the widths of the clouds here varies between around fifty and two hundred kilometres, I don’t know how that scale compares to the clouds in our own sky. It does sound rather larger at first consideration. I’m also tempted to see them as having been streamlined by the powerful winds and feel they don’t have much chance to be wispy, unlike Earth’s cirrus clouds. They’re almost like contrails in a way.

One theory about Neptune’s clouds is that the planet’s atmosphere is effectively a giant cloud chamber. A cloud chamber is a delicately balanced humid atmosphere used to detect subatomic particles, whose energy as they move through it leaves wakes in the form of clouds. This can be created using the steam from dry ice. The planet in question is of course very cold at the height the clouds can be seen, and it’s been theorised that galactic cosmic rays stimulate the atmosphere into producing these streaks. The coolness of the atmosphere makes these things much more significant for Neptune than here, so if this is how it happens, the cause is similar to the high winds. Ultraviolet light from the Sun is also probably responsible for features in the atmosphere, but probably the haze more than the clouds.

The rate of rotation has the same features as that of the bigger gas giants, as the planet does not rotate as a solid body would. The magnetosphere can be taken as a guide to the rotation period if you like, but it isn’t necessarily any more “real” than anything else and we only think it is because we’re from a planet with a solid surface and a shallow atmosphere. The magnetosphere takes sixteen hours, the equator eighteen and the poles twelve. All of this also raises the question of whether it even means anything to assert that Neptune has powerful winds. Maybe that’s just the rotation of the planet, which varies, but it doesn’t mean they actually amount to winds just because different parts rotate at different rates. The understanding of fluid movement used with Jupiter, that they’re cylinders rotating independently, actually cancels out the idea that there are such winds, although there could still be slipstream areas where the wind would be felt.

Unsurprisingly, the interior of the planet closely resembles the other ice giant’s. As I mentioned before, Olaf Stapledon described Neptune, important in ‘Last And First Men’, thus: “. . . the great planet bore a gaseous envelope thousands of miles deep. The solid globe was scarcely more than the yolk of a huge egg.” The upper atmosphere is mainly hydrogen and helium with some methane. Deeper inside is a liquid, becoming solid, layer composed of water, ammonia and methane, and at the centre is a core somewhat larger than Earth made of silicate rock and iron. Like Hamlet, it probably rains diamonds and there are likely to be diamond-bergs floating in the ocean. There may even be a whole layer of diamond deep within the planet.

There being two similar planets of this kind in the system might be seen as coincidence, but in a cosmic context seems not to be. In fact, Neptune-like planets are more common in the Galaxy than Jupiter- or Saturn-sized ones, and the fact that only one spacecraft has ever visited either hampers understanding of a disproportionately large number of worlds. There are nearly 1 800 known Neptune-like planets, notably referred to as “Neptune-like” rather than “Uranus-like”, which makes me wonder again about that ridiculous name although Neptune is more “typical” seeming since it isn’t tipped on its side. Even more common, and absent from the known Solar System, is the intermediate-mass type of planet both smaller than Neptune and larger than Earth. Some of these are much closer to their stars than our own ice giants, and can’t therefore really be classified as such. Nonetheless, this size and mass of planet is common in the Universe.

Getting back to our own Neptune, one surprising finding was that like Hamlet’s magnetic field, Neptune’s is off-centre and at a radically different angle to its axis of rotation. This creates another puzzle because the orientation of Hamlet’s magnetosphere was attributed to its peculiar tilt and misadventure with a large body in the distant past, but given that Neptune’s is also like that suggests that this is irrelevant and makes me wonder if that ever happened, although the tilt does need to be explained. It’s offset by 55% of the planet’s radius and the magnetic poles are 47° from the axis of rotation, yet no explanation based on collisions or close encounters with large objects has been offered so far as I know.

That said, Neptune does in fact show some evidence for this. Discounting Pluto and Charon, the planet has the largest proportionate satellite of any planet in the system but Earth, namely Triton, which is also the only large moon to orbit backwards, and appears to be a captured dwarf planet. Also, the moon Nereid has a comet-like orbit with its closest approach to the planet being much greater than its greatest distance, making it elongated and highly elliptical. Hence one catastrophe may have occurred to Hamlet and another radical event to Neptune, and the question then arises of what was happening in the outer solar system early in its history. Neptunian auroræ are not distributed like terrestrial ones due to the different magnetic field and the presence of rings, which reduces the quantity of charged particles trapped in the magnetosphere. Neptune and Triton also interact magnetically in a similar manner to Jupiter and Io, although not so strongly. There are diffuse auroræ close to the equator to just over half way to the poles, and more definite rings of auroræ closer to the poles, and brighter near the south pole at the time of the Voyager 2 encounter. Neptune has the weakest magnetosphere of any gas giants.

As mentioned above, Neptune has rings. Once Jupiter’s rings had been discovered by the Voyagers, Hamlet already having had them detected, it seemed inevitable that it would have them too, and it has. They were discovered from Earth in 1984 CE but had been seen occulting a star in 1981 in a manner compatible with them not being complete. That is, it was established that there were curved objects orbiting the planet but not that they went all the way round. This is probably because their width varies more than the other three planets’. There was an uncomfortable period in the early ’80s when for me it seemed inevitable that Neptune would be ringed but there was no evidence either way on the issue. I wanted the giant planets to be uniform. For some reason its ringedness is less emphasised than the others’, maybe because it had become routine by that time and it would’ve been more surprising if it hadn’t been.

There is no uniform scheme for naming planetary rings, as can be seen with Hamlet’s. Neptune’s are named after astronomers associated with the planet, specifically Galle, Le Verrier, Lassell, Arago and Adams. Adams is the one with the wider arcs, which are named Liberté, Egalité, Fraternité and Courage. Egalité is split into 1 and 2. Three small moons orbit between the rings, and there’s another ring associated with the moon Despina. In a way it’s quite nice that there’s a French theme to the naming contrasted with the English theme for Hamlet, but I don’t know if it’s deliberate. One really surprising thing about them is that the supposèd “discovery” was actually an occultation by the moon Larissa, so although they were correct about them being rings, they were correct by chance and misinterpretation of an unusual astronomical event. Neptune is a harder target for ring detection than Hamlet, although that is itself not easy, because it moves so slowly against the background with its 165-year orbit. The rings are, like the other ice giant’s, very dark and of course even dimmer due to the greater distance from the Sun. There’s a big contrast in the widths, with the three inner rings being only about a hundred kilometres wide (i.e. their height) and the others being several thousand, which is unlike Hamlet’s much thinner ones. An image of them with the contrast turned up to show details of the structure looks like this:

It’s really come to something when a planet invisible to the naked human eye is made so bright that its glare almost bleaches out the view of its even dimmer rings. This is a ten-minute exposure made by Voyager 2, which was right there, and still the rings are hard to see without that kind of technique. Whether the average human eye could see them is another question, as ours are very good at adjusting to low-light conditions. It still isn’t that low though, at least compared to bright moonlight, but I fear I’m repeating myself. In fact, all the conditions that apply to sunlight on Pluto also apply to it on Neptune because their orbits overlap distance-wise (they don’t literally). Hence the Sun at Neptune’s distance is just a star. The minimum visible object to someone with good vision is one minute of arc across. After that, it’s visible if it’s luminous but not as an actual shape. This is equivalent to a hair’s breadth viewed from twenty-five centimetres away. From Earth, the Sun appears as a disc thirty times that diameter and is therefore very obviously a ball of light. Neptune, however, is thirty times as far away and the Sun could therefore not be seen as anything more than a star, which is effectively a point source of light. This is, however, quite misleading as it’s still many thousand times as bright as any other star in the sky, and might therefore not appear as a point due to its glare. Lighting conditions on Pluto have been likened to those on Earth after a sunny day shortly after sunset, so the same kind of thing can be expected on Neptune and its moons. In other words, you’d probably hardly notice it at all after a while and it would look like broad daylight, except that the actual illumination is only a thousandth that of the Sun’s here. Looking at it from the other end of the telescope, as it were, Neptune is the only planet in the system, taking Pluto as a non-planet, which is never bright enough to be seen. Its maximum brightness is something like four times dimmer than it would need to be to become visible. Of course there will, as with other celestial bodies, be other species who can see it and in fact Galileo saw it, through a telescope of course, but didn’t notice it was a planet. Likewise, it was reported that it had rings shortly after it was discovered but in this case it was probably an illusion.

Neptune has a rather odd array of satellites. At one point it was thought that Triton might be the largest in the Solar System, and as I mentioned above it orbits backwards compared to most other moons. Nereid has a very eccentric orbit. Up until the 1980s, these were the only two moons known, but Voyager 2 surprisingly discovered a moon, now called Proteus, which is actually larger than Nereid, making it the largest object discovered by the Voyager probes. Due to the mistake leading to the accidentally correct conclusion that the planet has rings, the moon Larissa was also detected in 1981 but it wasn’t realised that this had happened, rather like Galileo and Neptune itself. Voyager 2 found another five, including Proteus, and a further six were discovered this century. Neptune also holds the record for having the most distant moon and the longest time taken for that moon to orbit, Psamathe, which is fifty million kilometres from it and has a period of almost twenty-five years. There are various interesting things going on with Neptune’s moons but that can wait until my next post.

Probably the most prominent appearance of Neptune in science fiction is in Olaf Stapledon’s ‘Last And First Men’. Published in 1930, the science is well out of date, although the description of a yolk in an enormous egg is valid. In this account, our distant descendants are living on Venus an æon hence when they observe a mass of gas on a collision course with the Sun which will cause the Solar System to be disruptd and the Sun to become what we would probably call a red giant the size of the orbit of Mercury. Humanity decides, though not en masse, to escape to Neptune, where it has to contend with enormous gravity and pressure, and first a very cold climate followed by a very hot one. Humans cease to be intelligent and take four hundred million years to evolve into a sentient form again. This is partly because their lifespan is much longer, as most species live at least one Neptunian year. They ultimately become superhuman beings who notably have ninety-six genders and a life expectancy of a quarter of a million years. I find this section of the novel, if that’s an accurate description, to be a particularly satisfying example of speculative evolution, although one which has been left standing by scientific discoveries about the planets involved.

That’s probably a fairly adequate introduction to Neptune. Next time: Triton.