I Was playing space engine and i was looking for a planet like Earth for quite some time and then i stumbled on this beautiful world covered with liquid water which orbited a main sequence star with 8 other planets that ticked most of the boxes for human survival, with a small plot of land. This planet is 77% Earths diameter, 0.47 times Earth's mass, 0.78 G surface gravity, and its Rotational period is 2.3 earth days about (55 hours long) and its orbital period is about (766 Earth days) in total, and its temperature ranges from 25-38 centigrade. Even with these close similarities it was the atmospheric composition which caught my eye, its atmospheric pressure is 0.5atm (Half of the earths surface pressure) and its atmospheric composition consists of: N2 = 40.5% CO2 = 31.4% O2 = 26.4% H2O = 1.5% SO2 = 0.136% CH4 = 955 ppm C2H6 = 75.5 ppm

Are these conditions safe for human beings to live in?This is a picture of the planet

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    $\begingroup$ That's a MASSIVE amount of CO$_2$ in that atmosphere! 31% CO$_2$ is unlikely to be survivable for humans, though I don't have any data at hand to back that up and don't have the time at the moment to dig it up. $\endgroup$
    – user
    Commented Sep 26, 2016 at 16:59
  • $\begingroup$ Yeah I was worried about the level of carbon dioxide $\endgroup$
    – JDAstro
    Commented Sep 26, 2016 at 17:00
  • $\begingroup$ Is this related to worldbuilding.stackexchange.com/q/55875/29? How about you just take Earth's atmosphere and give it a few tweaks here and there? The planet looks sounds at first glance, except quite warm for its distance from its star but that would depend a lot on the star. $\endgroup$
    – user
    Commented Sep 26, 2016 at 17:02
  • $\begingroup$ Well i found another problem. this specific body is located within the galactic centre of the milky way galaxy so there would be over 10 million stars or more per 10-5 light years $\endgroup$
    – JDAstro
    Commented Sep 26, 2016 at 17:05
  • $\begingroup$ It was a good idea though $\endgroup$
    – JDAstro
    Commented Sep 26, 2016 at 17:06

1 Answer 1



31.4% CO2 is way too high. According to Wikipedia, you can last about 0.1 hours in 7% CO2, and that's even when there's otherwise enough oxygen in the air. I think plants would be able to survive it, so if you seed the planet with enough plant life you could bring down the CO2 levels to make it habitable within a century or two.

The SO2 levels are also way too high, and I'm not sure how you'd take care of those. Based on the Wikipedia page for SO2, a safe level is 75 parts per billion (0.0000075% instead of your 0.136%). "Sulfur dioxide emissions are a precursor to acid rain", so this also makes it harder for plants to grow, making it harder for you to get rid of the CO2.

  • $\begingroup$ Yeh iv been searching for over an hour now and not one single planet that i have found with life has carbon dioxide levels below 7% although i found one moon with a warm temperature that had 7.2% carbon dioxide. They are so rare $\endgroup$
    – JDAstro
    Commented Sep 26, 2016 at 18:07
  • $\begingroup$ The Co2 levels of our Earth are 0.04% so for humans i imagine we would die quite quickly without very good filtration systems. en.wikipedia.org/wiki/Carbon_dioxide_in_Earth's_atmosphere $\endgroup$
    – Sandy
    Commented Jan 11, 2017 at 21:14

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