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The theoretical world of Hēdran is the 2nd planet of a 7 planet system. It lies within its star' s (G1.4) habitable zone, but with a hot jupiter gas giant only ~1 AU away it experiences heavy gravitational flux (this will be important later).

Hēdran is the remnants of a carbon planet and as such it is already rich in hydrocarbons, but for the majority of its life is has been an oxygenless barren world. Until planetary drift occurred bringing one of he gas giants to the innermost orbit. Hēdran was spared annihilation but was instead seeded with liquid water and other chemicals necessary for life.

Now eons* later it maintains an atmosphere slightly different to our own

Atmospheric content

As mentioned before the planet receives more than the usual amount of gravitational flux due to the close gas giant. This has caused an increase in volcanism and geological activity. This is how I explain the replenishment of gasses such as SO2 and N2O, also a unique property of the planet is that it is inherently high in metals.

How these conditions might affect life will come in another, later, question.

Main question at hand

It is planned (though subject to change) that the bioavailable heavy metals (Platinum, Palladium, Chromium...) has led to the ability of complex life to be able to catalyze normally toxic gasses for use in biochemistry. For clarity's sake, yes photosynthesis and respiration will take place to replenish and reuse atmospheric gasses.

Given that life found a way to catalyze and use the gasses listed are there abiogenic reasons why my atmosphere would be unstable and eventually decay?

*Using Eons as a euphemism for an indeterminate passage of time

Austinman42
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  • I think N2O is a function of N2 and O2 and UV; other than that, the atmosphere looks A-OK to me. –  Aug 25 '22 at 10:42
  • "Eons later" a carbom planet would IMHO assimilate all the water+oxyden deployed over it during a gas giant relocation, and remain a lifeless planer with atmosphere mostly containing N2, noble gases and possibly CO/CO2 or CH4 released from carbon core, in case there was not enough oxygen to turn entire planet crust into CO2. Your 24% O2 look illogical if your crust is carbon, this amount would cause carbon crust to burn quickly, reducing O2 percentile to way lower value. – Vesper Aug 25 '22 at 12:11
  • O2 is very reactive. Unless there is something releasing it (e.g. photosynthesis) I would expect the O2 levels after an eon to be way lower; most of the original oxygen would have combined with sulfur, carbon, metals... – SJuan76 Aug 25 '22 at 21:39
  • @Vesper Maybe I should stop referring to it as a Carbon Planet? I was mainly looking for something already in the scientific community that could explain pre-existing hydrocarbons without "because I said so". – Austinman42 Aug 25 '22 at 23:06
  • @SJuan76 Thank you, edited for clarification. – Austinman42 Aug 25 '22 at 23:32
  • Pretty sure that much nitrogen dioxide in the atmosphere is going to be blocking out a lot of the light. – KaffeeByte Aug 26 '22 at 00:09
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    Nearly all planets have water, you don't need to justify water, it is the third most common substance in the universe. the few that don't start with water but lose it because they are so hot and small water vapor reaches escape velocity. – John Aug 26 '22 at 03:36

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Frame challenge

with a hot jupiter gas giant only ~1 AU away it experiences heavy gravitational flux [...] As mentioned before the planet receives more than the usual amount of gravitational flux due to the close gas giant. This has caused an increase in volcanism and geological activity.

For this to happen your planet has to orbit the gas giant. If it is not orbiting it, the gravitational perturbation caused by the gas giant will soon kick the planet out of its orbit and throw it either in the star or in outer space, which in turn would probably cause the atmosphere to be deeply affected.

Just for reference, Mars is 1.5 AU from the Sun and Jupiter is 5.2 AU. The space between them doesn't have any planet because Jupiter prevented it from forming, and it's more than the 1 AU you are putting in.

L.Dutch
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  • for a better reference the asteroid belt is 2.6 AU from Jupiter, so the planet will be thrown or torn apart or both. – John Aug 26 '22 at 03:39
  • @L.Dutch Hmmmm thank you for the insight. Is there material or supporting evidence I can read up to refine my system for the better? I will more than likely be making a separate post on this topic. – Austinman42 Aug 26 '22 at 04:25
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    It might be possible that the planet could be in a stable Trojan orbit with the gas giant. It would share the same orbit as the gas griant but orbit 60 degrees ahead of or behind the gas giant. I am uncertain whether the rlative masses of he star and the two palnets would work for a trojan orbit to be stable. You might need an expert opinion on that. https://en.wikipedia.org/wiki/Trojan_(celestial_body) – M. A. Golding Aug 26 '22 at 06:21