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Setup

Ilithyia is a fictional super earth orbiting Eta Cassiopeia A, otherwise known as Achrid. She is 1.73 times larger than Earth and orbits closer to her host star, with a solar irradiance of $2300 \frac{W}{m^2}$. When the story takes place the atmospheric surface pressure is ~0.3 bar and the exoplanet is virtually devoid of $H_2O$.

Problem definition

The fact that Ilithyia has almost no $H_2O$ is fine in isolation, but it becomes paradoxical with the low pressure. Lets take a step back and examine what Ilithyia´s early planetary evolution most likely resembled.

Shortly after her formations large oceans formed, similar to Earth and Venus. These oceans quickly evaporated due to the high solar irradiance, triggering a runaway greenhouse effect. On Earth and Venus this caused atmospheric pressures to surpass 100 bar. Ilithyia is a lot larger than either, so pressures would be lower. Around 30 - 40 bar. On Earth, tectonic activity, water, and life bonded atmospheric $CO_2$ into solids, most commonly calcium carbonate through lithification. This did not happen on Venus. There, $H_2O$ was broken apart by the sun and the hydrogen carried away into space. Something similar would have happened on Ilithyia.

This is where the paradoxic requirements come in play. Ilithyia having little water is reasonable. The atmosphere being this thin isn't. Ilithyia is very large, and without oceans, plate tectonics would have shut down. Simply speaking, there is no geological process left to remove $CO_2$ from the atmosphere. Ilithyia should look like Venus, but she does not. What happened? Where is the $CO_2$?

Life... uhm... finds a way

The primary difference between early Venus and Ilithyia is life. On Ilithyia life evolved as soon as the oceans formed. It used thermosynthesis to power its glucose-producing biochemistry and did not evolve multicellularity before the oceans evaporated.

Thermosynthesis might be the saving grace here because the one thing "Venus" Ilithyia isn't short of is a massive, readily available, thermal gradient. On Earth, deep sea life often exploits convection currents around hydrothermal vents for chemosynthesis. Something similar would happen here: life could ride convection currents to dip in and out of the lower atmosphere, pick up heat, and perform work in the stratosphere.

The biochemistry life uses cannot exist in the lower atmosphere. Glucose, for instance, would just decompose. So it would have to evolve a thermal insulation layer around the cell wall. A foamy / spongy material like aerogel or Starlite. This works on a surface level but does not directly solve the core problem. Life is the only way to remove $CO_2$ from the atmosphere. But to do so, it has to bind the gas into a solid by itself. On Earth most calcite is made by sediment, organic materials, undergoing lithification. This does not happen on Ilithyia. There cannot be a sediment in-between step. When life dies, what it leaves behind has to permanently trap carbon dioxide. The only way I can see this working is if the thermal insulator unicellular organisms evolve is itself made of $CO_2$ and doesn't break apart under the surface conditions. So, when these organisms die, their thermal insulator remains and over the eons they slowly bind most $CO_2$ in it.

Requirement Hell

Let's take a step back and examine what I need this thermal insulator to be, and you will see why it has been difficult to find one. It must:

  • utilize Carbon
  • be resistant to large temperatures, pressures, and acidic conditions for an extended period of time
  • be capable of forming aerogel-like structures to perform well as a lightweight insulator
  • be "manufacturable" by a unicellular organism

There are loads of organic insulators which could work, but those won't last long enough on the surface to trap $CO_2$. Similarly, those materials which do trap $CO_2$ like calcite don't make great aerogel material. Looking at real world "Starlite" derivatives those often use baking soda, otherwise known as sodium bicarbonate. The issue there is that these are more ablative materials. $NaHCO_3$ decomposes to $Na_2CO_3$ at only a few 100 degrees Kelvin, which then decomposes into $CO_2$. Great for carrying away heat, not so good if you want to trap the $CO_2$.

The Chemical Garden

There are two silver linings to this. First, thermosynthesis once again comes in clutch. Since we assume that the organisms exploit the atmosphere's thermal gradient it is also safe to say they have access to the whole range of chemicals within it. While Ilithyia has no tectonic activity, there are massive volcanic traps spewing out chemicals. For instance, the solution could include magnesium even if we wouldn't expect to find any of that in the stratosphere.

Second, the solution doesn't have to be one size fits all. I don't think the most evolutionary sound strategy is to build a rock around a cell. For all I care, the thermal insulator can be decomposed 90% by the atmosphere so long as some of it traps $CO_2$. To give an example, maybe the insulator uses calcite pebbles woven in an otherwise organic / regrowing lattice. The lattice would break apart once the organism is dead, but the calcite pebbles remain. That would be a "good enough" solution. But I have no idea if that is reasonable.

Hard Sci-Fi?

I tagged this as science-based because there is no hard sci-fi. For all we know a seemingly perfect solution could be invalidated by some weird chemical reaction that only happens on an exoplanet of this mass due to unknown reasons XYZ. Moreover, the moment life is involved simplistic assumptions about the atmosphere do not apply anymore. We don't know what the exact transition from a liquid to gaseous habitat in Ilithyian life did to the atmosphere and that is just impossible to find out.

What I am looking for is a solution that fits the criteria described above. The most important thing it has to do is offer one path for $CO_2$ removal.

Thank you for reading, and any help!

EDIT: Details as requested:

For Ilithyia:

  • Day length: 11.32 hours (no natural moon)
  • Atmospheric height during "Venus" phase: ~200 km
  • Temperature laps rate similar to Venus, so 700-ish Kelvin on the surface, drop to about 300-400 Kelvin 30-40 km up

Regarding life, this is more speculative. I would suspect the unicellular organisms have to be relatively large, perhaps starting at 10 micrometers. This is based on the insulation layer.

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  • $\begingroup$ I much prefer "the life evolved to thrive in these conditions" over "the life evolved to create as Earth-like conditions as possible at all costs just to barely survive." As an example of what life near water's critical point is like, and how it would feel different to organisms adapted to that environment, that gets the physics mostly right: en.wikipedia.org/wiki/Close_to_Critical $\endgroup$
    – Kevin Kostlan
    Commented Sep 5 at 1:07

2 Answers 2

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No thermal insulation works in cellular size. Reason is very simple, no matter exists to insulate hundreds of grads in a micron size. In the world of the unicellular beings, temperature is a property of the Universe, like the speed of the light for us, and there is no way to change it in any direction.

I think you need multicellular beings, with a wide insulator layer could work. Probably you need also some floating mechanism. Both are known already in the current world.

You also need some really good water collecting mechanism to suck all the water molecules. It will be probably hard but maybe no impossible.

That could work, but... sometimes, Nature is not easy. Life can survive in a lot of places. Life can survive in a vulcanic throat. But, Africas western coast is just dead. There is water, although salty, there is fitoplankton, capable to survive in the salty water, but on the coast, there is not a thread of grass. Since ten millions of years. Why? Maybe the Biology SE knows the answer.

In many cases, it could work. Sometimes it can not. No one knows the answer. Very likely, they need a really good water collection mechanism. They also need some mechanism to collect soil from the probably really hot surface.

I imagine large, floating plants with long, modified pneumatofora to collect the dust from the surface.

I think, finding such beings on a foreign planet would be a really strong argument for the creationism.

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  • $\begingroup$ Can you elaborate on your first point ? It dosnt really sound right to me, why would an insulator not work ? It will be less efficient sure, because it is smaller, but not working at all ? $\endgroup$
    – ErikHall
    Commented Sep 4 at 18:10
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    $\begingroup$ @ErikHall Thermal insulation increases linearly with the layer width. In the current Earth, thermal insulation is mostly used by warm-blooded animals in cold sea, and they use at least some cm wide fat for that. That creates a some 10C thermal gradient. If you want the same in micro wide, you need a 10000 times better thermal insulator as fat. This matter does not exist. It is like density. If you want a heavier wight as water ballon (density: 1) you can try to use beton or iron (density: 8). If you re really rich, you can try to use osmium (density: 22). If you need density of 1000, you lost. $\endgroup$
    – Gray Sheep
    Commented Sep 4 at 19:16
  • $\begingroup$ back to the drawing board 😭😭😭 $\endgroup$
    – ErikHall
    Commented Sep 4 at 19:19
  • $\begingroup$ @ErikHall You can make them multicellular and you are fine. It can be also a lychen. Lychen is a symbyotic lifeform of unicellular plant and mushroom. $\endgroup$
    – Gray Sheep
    Commented Sep 4 at 19:36
  • $\begingroup$ After having given it some thought, idk how i ever thought a micron thickness shell was going to protect against Venus conditions. Like... if that was the case surly out probes wouldnt have melted ? xD Regardless, yeah ill go the route you suggested. $\endgroup$
    – ErikHall
    Commented Sep 4 at 19:50
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Frame challenge: an insulator is not a solution for your problem.

An insulator works decently to reduce heat transfer, but given sufficient time all the bodies in an environment will reach an equilibrium temperature. Adding an insulator is simply shifting the overheating problem to somewhat later in future.

If you want to keep something constantly at a lower temperature you need a way to extract heat from it and dump it in the environment. Basically you want to have a life-based refrigerating cycle.

It'd be much easier to "just" have life evolve to thrive in those conditions.

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  • $\begingroup$ Well the idea would be that life dosnt spent a lot of time in the lower layers. Instead it only goes there to "pick up" heat, basically heat up the shell, and then go back up. Either through currents or active mechanisms. Such that they can cool down and perform work. Right Thermosynthesis only works if you have a gradient. $\endgroup$
    – ErikHall
    Commented Sep 4 at 14:41
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    $\begingroup$ The scale of the organisms - you'd only have them in the lower atmosphere for milliseconds at most. How do you suppose they might travel so fast between layers? @ErikHall $\endgroup$
    – Escaped dental patient.
    Commented Sep 4 at 15:02
  • $\begingroup$ @Escapeddentalpatient. dosnt have to be milliseconds. Depending on the insulator it could be relatively long. Unlike Venus, Ilithyia has a fast day night cycle too. So the wind patterns are easier to exploit. $\endgroup$
    – ErikHall
    Commented Sep 4 at 15:08
  • $\begingroup$ Could you give us figures regarding the height difference, organism size then? Unless you'd prefer the [science-fiction] or [science-fantasy] tags over the [science-based] one. @ErikHall $\endgroup$
    – Escaped dental patient.
    Commented Sep 4 at 15:21
  • $\begingroup$ @Escapeddentalpatient. done, though this is all very speculative naturally. If you want something specific lemme know, thanks for the help $\endgroup$
    – ErikHall
    Commented Sep 4 at 15:33

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