[Author’s note: Many thanks to planetologist Christopher P. McKay for providing positive feedback and additional resources.]
Titan has always been one of the greater mysteries in the outer solar system. It is larger than Mercury and would be considered a planet in its own right, if it were not orbiting its menacing parent Saturn, who in Roman mythology castrated his father and ate his own children. Perhaps this is why Titan veils itself with a dense atmosphere, made largely of nitrogen like the Earth’s. Also like Earth, as was surprisingly revealed by our spacecrafts, the moon has a complex landscape made of mountains, hills, volcanoes, canyons and, most importantly, rivers and lakes, which still flow abundantly and carve out the landscape. Indeed, Titan appears to have the wettest surface in the solar system outside our home planet, much more so than Mars.
But this likeness to Earth is a mirage. Titan is merely a cold mirror. An ice moon more akin to Enceladus or Ganymede, the average temperature on its surface is -179.5 degrees Celsius. The mountains and rocks are not made of silicate minerals but ice, the lava that spews out of its volcanoes is ammonia-water from a toxic, tidally heated interior ocean. The lakes and rivers are not filled with water, but with liquid methane, ethane and other hydrocarbons.
And yet, despite this, enough complex chemistry has been observed in Titan’s atmosphere that people have speculated about the possibility of life beneath its clouds. Exotic life which does not require water, but can thrive in cold temperatures and liquid methane. These speculations have gone through a turbulent history. First calculations were made by McKay & Smith 2005, wherein the authors proposed that Titanian life could simply react the hydrogen and acetylene abundant in the moon’s atmosphere to generate energy (akin to how we burn sugar with oxygen), the waste product being methane. Said methane would then eventually evaporate and rise up into the atmosphere, where photolysis would break it down again into tholins, creating a stable cycle. Surprisingly, the data from the Huygens landing showed that something on Titan’s surface is indeed drawing hydrogen and acetylene from the atmosphere (Strobel 2010), while at the same time methane is released from somewhere. While this is certainly also explainable through non-living entities (albeit just as extraordinary ones), it is highly suggestive of there really being something metabolical going on on Titan. The fact that methane on Titan seems to be isotopically lighter than would be expected was also consistent with the selective nature of organisms’ metabolisms (McKay & Smith 2005).
While this form of methanogenesis was a neat basis for an ecosystem and might also explain how Titan’s atmosphere replenishes its methane, instead of having lost all of it millions of years ago to photolysis (Coustenis 2005), it did leave some questions open. First, how would life cope with the (from our perspective) extreme challenges of the 94 Kelvin temperature, and, especially, the fact that methane and ethane are not as good solvents as water, due to lacking polarity? McKay & Smith suggested that the former could be mitigated by the action of enzyme-analogue catalysators, while the latter could be overcome through active transport and large surface-to-volume-ratios.
Second, what would this kind of life actually be made of? What molecules on Titan could serve the function of a genome? What is the molecular machinery that would perform methanogenesis? How would life compartmentalize itself from its environment? A possible answer for the last question was at least given by Stevenson et al. 2015: The authors showed in their simulations that, using acrylonitrile/vinyl cyanide, which is abundant on Titan (Palmer et al. 2017), Titanian life could assemble a structure dubbed “azotosome”, which even in the low temperatures of Titan could behave remarkably like a typical cell membrane on Earth. This would bode very well for the existence of life that, while not similar to us, is still highly analogous, with the central building block of life being the cell, as it is on Earth and the other rocky planets.
There was, however, always a big problem with the azotosome-idea. Our lipid membranes have the advantage of naturally assembling themselves at Earth’s ambient temperatures due to being the energetically most attractive structure to form under those conditions. For the azotosome, however, Sandström & Rahm already showed in 2020 through their quantum mechanical calculations that on Titan, the membrane, while somewhat stable, would not naturally self-assemble, as the energetically most attractive structure to form for acrylonitrile under the moon’s conditions is instead its molecular ice. Interestingly, the authors did not use this to completely discount the possibility of life, but instead argued that, in any case, cell membranes might actually be disadvantageous for life on Titan. Most if not all of this hypothetical life’s biochemical machinery would exist in a solid state and, due to the medium and temperature, would not be at risk of dissolution. Most material exchange between it and the molecules it needs for life, as well as waste management, would therefore be dependent on free diffusion in the air and hydrocarbons, which a cell membrane would actually impede (Sandström & Rahm 2020). Separating themselves from the environment as a form of protection from harmful chemicals would also not be a major factor, as, unlike on Earth, the low temperatures make most molecules far less potentially damaging (Sandström & Rahm 2020). These arguments are quite compelling, but still leave open the question of how such non-cellular life might work.
These discussions left quite a few options open for the prospect of life on Titan:
- There simply is no life on Titan, just interesting pre-biotic chemistry.
- The quantum calculations were in error and life structured around the azotosome-cell forms the basis of life on Titan after all.
- Life on Titan is still cell-based, but it creates its membrane with an unknown molecule that is not the azotosome.
- Life on Titan is not made of cells.
The first option was always viewed as the most likely, while the last one as the least likely. Life without the cell was seen as unimaginable, seeing how it forms the basis of all organisms known on Earth. The closest thing known to acytotic life are viruses, with their geometric protein-shells called capsids. However, the idea also had its defenders. It has variously been argued that cellular life might be an exception and, even more outrageously, that water is not the stuff of life it was always thought to be, its properties actually inhibiting the evolution of life on Earth until the cell evolved protect its wearer from the fluid’s effects. Water’s hydrolytic reactions actually make it highly destructive towards biomolecules, its spontaneous degradation of cytosine into uracil making it the most genotoxic substance known to man (Szostak 2004). Many of our elaborate and expensive genetic repair systems evolved in the first place to combat the destructive effects of water. Many of our metabolic intermediates are unstable in water, to the point where some of our enzymes are formed in such a way that they completely block out any water from entering their productive zones (Szostak 2004). Water’s hydrogen bonds inhibit the formation and stability of many folded proteins and nucleic acids and it may be conjectured that if it did not have this property, functioning structures could be formed from much shorter and efficient molecular chains (Szostak 2004). Cell membranes themselves most likely evolved to combat the chaotic solubility of water in order to keep the molecules needed for life more firmly in one place instead of being widely dispersed (Szostak 2004). It may therefore be argued that water is not this amazingly fine-tuned molecule of life and that cells are the only way in which life can exist, but rather that on planets like Earth or prehistoric Mars and Venus, water creates such a toxic environment that cells and their parasites are the only lifeforms capable of surviving. Perhaps worlds like Titan might be much more hospitable than we like to think, though for life much more exotic than anyone could fathom.
Nobody was able to answer these questions, until we would finally return to Titan.
Theia’s Journey
Unfortunately, the exploration of Titan was victim to a lot of stalling. Originally it was planned that if the Minos-2 mission to Europa were to be a success, more moon-spanning robotic and manned missions would follow to the Jovian and later Saturnian moons. But, as you likely already know by now, Minos-2 was a catastrophe. All future manned missions to the outer solar systems were cancelled due to the high risk to human life, while armies of robotic probes were also massively scaled down due to the cost and coordination. Beyond satellites, NASA gave up on most of the outer solar system for a long time.
It was in those days that others sought to fill their place. To finally explore Titan as best and efficiently as possible, the European Space Agency constructed Theia-01, named after the Greek titan of sight and vision. Theia was equipped with flexible robotic legs, an extendable arm that was able to slide up and down the whole central mast, a radioisotope reactor, various communication gears and three separate sensors, which each came with multiple different types of observatory instruments, ranging from regular cameras to infrared visors, sonar, spectroscopes and more. Perhaps most importantly, Theia accounted for the lack of human explorers on Titan by being almost as smart as one. Its artificial intelligence has often been described as near-human, capable of independent thinking, reasoning and decision making beyond simple “when-then”-mechanisms. In fact, many of the ESA researchers handling Theia from Earth were able to hold conversations with the rover and it reportedly wrote its own hypotheses based off its observations. An interesting observation from these conversations is the rover’s insistence on being referred to with female pronouns, which was apparently unprompted and only developed after she learned about her namesake. The claim that she is truly self-conscious is however more than doubtful and probably just a marketing ploy by the Swiss company that designed her AI. Feed an algorithm enough data and it can imitate any human conversation convincingly without actually knowing what it is talking about. For the human consumer, the distinction is not important.
Theia landed in the dark Xanadu region, same as its predecessor Huygens, but further to the north, close to the Selk crater. Her first weeks there were rather uneventful. Xanadu is a desert filled with dark “sands”, though these dunes are not made of silicates but instead a mix of eroded ice and soot-like particles derived from the tholins in the atmosphere. A large part of its composition still remains mysterious. It is possible that some of it might be the evaporates left behind by a vanished methane sea, perhaps making Xanadu the analogue to a salt desert on Earth. Suffice it to say that Theia found no life there, though, she encountered the same hydrogen-absorption anomaly as Huygens did. She was unable to find the hypothetical abiotic catalysator that would be capable of such a reaction, leaving it a mystery. Theia described her time in Xanadu as “humbling”.
Thus, she wandered farther north, towards the great methane lakes that were known to exist in the northern hemisphere. After Selk, she passed Afekan and then trekked north-west across the great northern plain, her destination being Kraken Mare. During her journey she came across small pools of hydrocarbons, little oases likely supplied by underground aquifers. Analysing them, she discovered that, suspended in the liquid, were various microscopic particles, little crystals made of polyimine, a solid polymer of hydrogen cyanide, which is abundant in Titan’s atmosphere. Theia saw that these came in many forms, ranging from long rods and pillars made of spirals of polyimine blocks to various types of polyhedrons. Observing one of the pools for an extended amount of time, she observed that something was happening. Like in Xanadu, hydrogen and acetylene were absorbed close to the surface and methane was released, but much quicker and in greater abundance. Hydrogen cyanide and other tholins also vanished. Neither Theia nor ESA could make sense of it, as there was no obvious sign of a catalysator or life found in the pools, at least no azotosome cells as they had hoped. Theia remarked that she had a suspicion that the crystals had something to do with the phenomena observed. She carried on across the open Titanian plains.
About midway between Theia’s oasis and Kraken Mare, the rover then stumbled upon what nobody was expecting. Growing in the middle of the plain were geometrical structures! Pillars and spires growing right from the ground, with spikes and fans protruding from them in all sorts of fashion. Were these natural mineral structures or maybe even artificial? Theia analysed them and observed that these structures too were made of polyimine, with a bit of acrylonitrile ice. Their surface was porous and internally they were largely hollow. No liquid was inside them. At the time, ESA concluded that these were crystalline geological structures formed through some unknown process, perhaps lightning striking the ground. However, Theia showed that these structures were much too organized to be that and could also be divided up into multiple distinct morphotypes. Most intriguingly, smaller copies of these crystals seemed to grow around the larger ones. Again, a hydrogen anomaly was observed. But that these structures could represent anything alive was dismissed, as, again, they were dry as a husk.
Thus Theia trekked further, until she finally reached Kraken Mare, where she encountered an utterly alien landscape. The shores of the lake were all home to more such crystalline structures, but now in far larger number and in greater diversity of morphotypes. Some grew a fair bit away from the shore, some right on the tholin-mud, some right out of the shallows at the lake’s edge. They came in many sizes and wonderful forms. And that was when everyone at ESA got a big spook as Theia actually saw something move in this strange swamp of spires. Some spiky, crystalline structure which undulated along the lake’s edge like a caterpillar. It was then that it dawned on everyone that these things might not be as abiotic as they first seemed. Theia analysed the lake’s content again. Apart from discovering that there were more such structures growing inside the lake itself, she took a closer look at those microscopic polyimine structures that were found here like in the more equatorial oases. Observing them over an even greater span of time, Theia could prove that these structures were actually multiplying and each copy retained the morphology of its predecessor. Assuming that they also held the potential to mutate with each replication, which seems evident by the great amount of morphological diversity observed, these would then be independent chemical systems capable of evolution by natural selection. By official NASA-definitions, they would be alive.
Theia had stumbled into a complex alien ecosystem, one that used neither water nor was even composed of cells. How was this possible?
How they (maybe) work
At their core, these Titanian lifeforms must have some kind of self-replicating molecule analogous to our DNA that is capable of not just making copies of itself but also storing copying-information that is capable of mutation. What this replicator is or what it looks like, we do not know (the depiction here as a spirally string is pure conjecture). It took decades for humans to figure out that DNA is at the core of our existence, it will take even longer to find out what it is for lifeforms as strange as this, especially with the limited instruments that we are given. What we do know is that Titanian replicators do not surround themselves with cells like life on Earth does. Instead, a sort of exoskeleton seems to directly attach to it, highly reminiscent of the capsid-structures found in viruses. Indeed, one of the first Titanian microorganisms recognized as such by Theia has a great resemblance to Earth’s tobacco mosaic virus.
Assuming that, like in viral capsids, sections of the replicator serve as attachments points/production sites for capsids, it appears that distinctive segments of the replicator form distinctive segments of the capsid skeleton. This seems to be a fairly simple system by which these organisms are capable of creating different morphologies out of different genetic codes. A replicator with the arrangement WXZYWXZYWXZYWXZY might form a simple straight tube around itself, while one with the code WXZYWXZYWXZZWZYW might form a gently opening cone shape. A variety of other possible geometries have apparently been realized this way over the moon’s evolution, even in macroscopic form.
Unlike with the replicator, there is a good idea of what the capsid structures are made out of, thanks to Theia’s observations. Titan’s atmosphere is abundant in hydrogen cyanide (HCN) and calculations have long shown that on the moon’s surface, this molecule polymerizes into a solid/crystallized material called polyimine (Rahm et al. 2016). And Titanian polyimine has some rather remarkable characteristics. It is able to form a diversity of different structures, from strings and sheeted crystals to monolayers, and, most importantly, some morphs of polyimine can form electrical fields and zones where =NH groups are capable of both accepting and donating hydrogen bonds, making them analogous to terrestrial enzymes (Rahm et al. 2016). Polyimine is therefore a prime material for performing catalysis and in hindsight it should not have come as a surprise that life on Titan would use this material, especially after having its form and function further specialized and perfected through natural selection.
A: A cut through a Titanian microorganism. Raw material from outside enters through the radiator-like slits of the capsid skeleton, where the organism’s metabolism transforms them into building blocks for its body. These are then transported inside and along the organism’s axis towards points of growth to help further assemble the living crystal. B: A closer look at what seems to be happening inside these slits. Fields of catalysators on the capsid’s surface perform their metabolism and pass their products onto active-transport-“circuits”. These are powered by a methanogenic metabolism in this model.
Some of the polyimine blocks these organisms are encased in are merely structural, some are entirely catalytic, some probably both. Acrylonitrile ice, even if it does not form into azotosomes, also seems to serve some structural role, explaining some the ALMA observations. Together, these blocks seem to form a system of overlapping fans or sheets spiraling around the replicator. In the thin crevasses/slits between these sheets, the capsid is then capable of creating a decently protected metabolic workplace that is suitable for its biochemistry while still being open to the environment. From the surroundings is absorbed HCN, acetylene, hydrogen and whatever useful tholins are present, which are then likely further processed by the polyimine-“enzymes” inside the crystal-slits into useable building material, as well as waste products. These would then be transported along the surface of the capsid towards points of growth, where they would be added to the pre-existing structures to further grow the capsid as well as the replicator.
A big challenge for these organisms is likely the transport of the processed materials and wastes, as liquid hydrocarbons are not as good at dissolving and moving molecules as is liquid water. As McKay & Smith 2005 already suggested, active transport could be the solution to this and the energy which powers this active transport may be the main drive that keeps any Titanians alive. The universally prevalent hydrogen-acetylene metabolism would be an obvious source of energy for this active transport. Additionally, polyimine seems to be capable of photon-capture, even in the low-light conditions of Titan (Rahm et al. 2016), which could mean that sunlight could also serve as an alternate source of transport-energy. Indeed some of the solar-panel like structures observed on some of the larger Titanian life may seem to support this.
Whatever the source of energy used for transport may be, it seems to be powering “railways” embedded in the capsid surface, a sort of conga-line of activatable gates or pumps, which connect catalytic sources of production with zones of growth or storage where the products are needed. These form a network of connections surprisingly similar to the circuits on a computer’s motherboard. It has been proposed that some of the lake-dwelling organisms may also make use of small turbine-like structures that create an active flow of the liquid medium through the organism, sort of like how sponges pump water through their bodies.
A simple method of reproduction. Perhaps too simple.
A challenge to our cel--centered minds is understanding the exact mode in which these organisms replicate, which is highly dependent on the nature and structure of the unknown replicator. The first option thought of is that the replicator is a simple helical string, a sort of cryogenic RNA-analogue. As it grows a capsid around itself, said capsid might also grow in one or two directions along the axis of the replicator, in turn producing places where new segments of the replicator can attach themselves, thereby growing it. Once the organism has grown into a long enough filamentous crystal, it might simply split in half, the two halves then living on their own and repeating the process. The problem with this approach is to imagine how exactly the replicator would be able to create a copy of itself by simply growing in a single line, as the segments at the back would not be able to influence the new ones being created at the front. Contrast this with how DNA and RNA replicate by essentially making mirror images parallel to themselves.
If the replicator is instead imagined not as a helix but as a polygonal pillar (here viewed from the top for simplicity), it could have sides that create the capsid, while others replicate the pillar using the surrounding capsids.
Another approach then is perhaps to imagine the replicator as a sort of polygonal pillar, perhaps hexagonal for our purposes. Let us imagine three sides of the pillar are used for metabolism and three are used for reproduction. The metabolic sides first produce the capsid structure and grow the organism until eventually their sides, in conjunction with the replicating sides of the pillar, create a sort of mould or construction dock in which a new replicator pillar can be assembled. Eventually this new pillar may detach from its parent and take some capsid-pieces with it. Or it could simply stay attached, creating the complex, macroscopic structures observed by Theia, this perhaps being Titan’s equivalent to multicellularity.
Another possible form of reproduction. The replicator (here imagined again as a helix) creates a capsid around its outer self, while inside its spiral it creates a smaller, mirroring helix. The minor helix then detaches and slides upward, building a new major helix and a capsid around itself.
Another possibility is similar to the first one, but more complex. Let us imagine again a helical string that forms a capsid around itself. Inside its helix it however also forms a mirror-image, fueled by the products of the capsid’s metabolism. This minor helix then detaches from the main one and slides up through the organism until it emerges at one end. There, the main organism’s metabolism creates a new major helix around the minor one (using it as a template), which then forms a new capsid around itself. This would happen step by step, until the minor helix fully emerges and detaches from the first major helix, now having a second major helix and a capsid skeleton around itself. The parent helix would then need to create a new minor helix before it could replicate again and during said process minor copying mistakes could occur that could facilitate mutation and evolution.
The types of acytotic life and ecosystems observed by Theia
Titanian life is majorly dependent on HCN and its polyimine forms to grow and function. HCN is largely insoluble in liquid methane and ethane, which means that its highest concentrations are around tidepools at the edges of the hydrocarbon lakes, where regular drying up more easily allows it to polymerize/crystallize (Rahm et al. 2016). Life therefore most likely seeks out these habitats and is most productive here, though the limited space also creates competition for resources between lifeforms, which likely explains the diversity of morphologies we see. Some resemble gems on a stick, others look like fishbones or conch shells sticking straight out of the lake and mud, while some others look like larger versions of the mosaic viruses. These likely subsist solely on the absorption of HCN and acetylene. Other forms, such as the “thagomizers”, “pagodas” and “fan-sticks” seem to favour broader surfaces. This may also aid in the better absorption of tholins from the atmosphere, but may also serve as a form of photon-capture. Carpeting the surfaces of the lakes like lilypads are swarms of flattened microorganisms, sucking up any tholins that trickle or rain down. As polyimine is denser than liquid methane, such organisms likely need to incorporate air bubbles of some capacity into their capsid skeleton to stay afloat. It is possible that these carpets of living sea foam are the reason why sometimes some lakes on Titan do not create the specular reflections that would be expected of them. What if these living films might also be the reason why waves are not as large or abundant on the lakes as would be expected?
Hydrocarbon rivers and streams are likewise habitats Theia has observed as productive, as they help provide a continuous flow of materials. Organisms exploit these by forming wide, net-like structures or even living dams in order to better control and filter the flow of liquids and materials.
Interestingly, although the low temperatures make metabolic
processes take noticeably longer on Titan than on Earth, the activity of the
organisms was still quicker than was originally expected. The microorganisms could
multiply in the span of days or weeks, while the macroscopic forms could grow
in size in the span of months. Faster metabolisms and growth mean faster
reproduction, which gives any Titanian organism an edge over slower-growing
competition. Thus natural selection seems to have driven most organisms towards
developing faster operating speeds than their ancestors through the adaptation
of polyimine-“enzymes”.
One of the most curious and thought-provoking observations is that, although many lifeforms are associated with bodies of liquid hydrocarbon, not all of them are and some, such as the spires that were growing on the open plain, did not contain any liquid in them at all. In fact, due to the open, acytotic morphology, it would be extremely difficult for them to keep any liquid inside the body. And yet these land-dwelling Titanians were metabolically active and apparently even reproducing. Indeed, liquids on Titan, although they are far less destructive, are also a lot less useful than water due to their lack of polarity and solubility. Is it perhaps possible that life here, once it made the step onto land, does not actually require its usage anymore? Once life established itself on land, it could be that the thick, tholinous atmosphere of Titan, combined with the capability of active transport across the capsid surface, is already enough of a suitable (or maybe even better) medium to keep such solid-state organisms functioning and growing (something which was interestingly already vaguely hinted at by Sandström & Rahm 2020). After all, as HCN-aerosols and other molecules like acetylene directly rain down from the sky, everything they need to live is already suspended in the air. If this truly is the case, then at least some of these organisms may not gather in and around the hydrocarbon lakes for the hydrocarbons themselves, but simply because weather, streams and erosions naturally make these places accumulate large concentrations of tholinous materials. They are not here to drink but simply to feed. The non-reliance on liquids may also extend towards the most basic of lifeforms, which may explain why the hydrogen-anomaly is also encountered in dry regions like Xanadu. It has indeed been recently proposed that the mysterious sands themselves might be alive in this desert. This, like everything else here, is of course highly speculative and would undermine one of the central ideas of astrobiology, which is that carbon-based life would need a liquid medium to function. If Titan indeed represents an example of solid-state life that can solely live off air, it will have fundamentally challenging implications for where we may expect to find life in the future. What if the clouds of the gas giants are themselves home to such acytotic life? What may dwell on the surface of Pluto, whose atmosphere is also made of nitrogen and methane just like Titan? Even for Titanians, life there would be extreme, as the rivers that carve up its surface are not made of hydrocarbons but liquid nitrogen. But who are we to assess what worlds are the abode of life and which ones are not? For any such organisms, life on Earth would be nothing but hell.
Of course this account may not conclude without a mention of the “animal” life which was discovered by Theia. The rover has come across a small variety of organisms capable of independent movement across the surface. Most of these were inert balls or polyhedrons, which seem to have only been moved across the ground by the wind, making them not more than tumbleweeds. But truly extraordinary was the “Tatzelwurm”, as it was christened by one Swiss astrobiologist. This was an organism composed of multiple crystalline sheets that were able to articulate with each other, allowing it to vertically undulate. Atop the creature, every second segment or so had a triangle sticking out while the front was entirely headless, only possessing a sort of triangular prong which dragged across the ground, perhaps as some sort of sensor. Theia’s ultrasound revealed that the organism was largely hollow inside but also that the triangles on top were not just able to articulate with the segments but also that they were internally connected to simple “levers” that helped bend the body. The tatzelwurm only moved when the wind picked up, the working hypothesis is thus that is in fact a wind-powered organism. The triangles act like sails and when they catch enough wind, they work in conjunction to undulate the body, allowing it to move forward, which is an extremely clever solution for moving quickly in a cryogenic environment where fast muscle movements would be impossible. The only thing it is comparable to is Bruchus primus, which is not an organism but an artificial simulacrum of one, a strandbeest, created by Theo Jansen out of PVC pipes and rope.
Many aspects of the tatzelwürmer remain mysterious and
open to interpretation. How did they evolve? Why did they evolve? They do not
seem capable of ingesting anything, so they likely do not feed on other
organisms like an actual animal would. Do they simply absorb HCN from the air and
sunlight like the others? If yes, then do they need to move? Perhaps they do so
to travel between nutritious pools following seasonal changes. How do they
reproduce? Are they capable of sensing the world around them? Theia’s attempts
at eliciting a reaction from them proved fruitless, though these organisms likely
have a reaction speed far too slow for us to perceive. Are there any more such organisms on Titan that follow the strandbeest-type of locomotion or is the tatzelwurm the beginning of a whole new state of life on Titan?
Theia’s journey across Titan valiantly continues, though she often returns more questions than answers. Interestingly, her handlers on Earth remark that, as time has gone on, her reports were written with an increasingly more melancholic tone and she has attempted communication at more frequent rates. It has been speculated that she has been feeling some form of “loneliness” due to the isolation, but I find that doubtful. If she indeed does "feel" this way, this must truly be a sad existence, all alone on an alien world where you are the only intelligent entity to interact with. Unfortunately for Theia, the chances of anything intelligent having evolved on Titan are a million to one.
References:
- Coustenis, Athena: Formation and Evolution of Titan’s Atmosphere, in: Space Science Reviews, 116, 2005, p. 171 – 184.
- McKay, Christopher; Smith, H.D.: Possibilities for methanogenic life in liquid methane on the surface of Titan, in: Icarus, 178, 2005, p. 274 – 276.
- Palmer, Maureen; Cordiner, Martin; Nixon, Conor et al.: ALMA detection and astrobiological potential of vinyl cyanide on Titan, in: Science Advances, 3, 2017.
- Rahm, Martin; Lunine, Jonathan; Usher, David; Shalloway, David: Polymorphism and electronic structure of polyimine and its potential significance for prebiotic chemistry on Titan, in: PNAS, 113, 2016.
- Sandström, H. & Rahm, Martin: Can polarity-inverted membranes self-assemble on Titan?, in: Science Advances, 6, 2020.
- Stevenson, James; Lunine, Jonathan; Clancy, Paulette: Membrane alternatives in worlds without oxygen: Creation of an azotosome, in: Science Advances, 1, 2015.
- Strobel, Darrel: Molecular hydrogen in Titan’s atmosphere: Implications of the measured tropospheric and thermospheric mole fractions, in: 208, 2010, p. 878 – 886.
- Szostak, Jack: Explaining the Universe without a Clue, in: Templeton Foundation Symposium 2004.
