Does Mars have the gravitational wherewithal to support a breathable atmosphere?
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Nullo (
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August 7th, 2012
I know that the current one is little better than hard vacuum. I suspect (not having taken any physics) that since its mass is ⅓ of Earth’s, and its gravity ⅓ g, its greatest amount of air pressure would only be about 253mmHg at what amounts to Martian sea level.
Surely there’s more precise data that my guesses.
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11 Answers
I don’t think so but I will check with my sources.
Note that Venus maintains 9300 kPa surface atmospheric pressure with 0.904 g surface gravity versus 101 kPa and 1 g for Earth, i.e. Earth could have a much thicker atmosphere than it currently does (and fortunately for us, it does not).
A correction to the post: I’m guessing that the greatest tenable (and presumably breathable) atmospheric pressure would be 253mmHg. @hiphiphopflipflapflop Venus’ atmosphere does nobody any favors.
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Mars used to have a lot more atmosphere but that was because a lot was being created by geological processes that have since slowed down.
Solar wind has stripped most of that early atmosphere from Mars.
Earth has the atmosphere that is does for two reasons one is the gravity, the other is the magnetosphere around earth that lucky for us deflects much of the solar wind away so that it does not take so much of our atmosphere with it. Earth’s strong magnetosphere results from churning of its iron core. Mars does not have an iron core and has negligible magnetosphere to protect us.
@dabbler I’ve read that Earth has one of the weakest magnetic fields. You could be right but I don’t know.
Apollo spacecraft had 253mmHg atmosphere, but it was 100% oxygen. The astronauts did fine.
I don’t know how well O2 would stay in the atmosphere of Mars, given Mar’s low gravity. CO2 has higher density so may be easier to keep.
Humid air at sea level contains a partial pressure of oxygen of around 150 torr (20 kpa). You need this to stay alive. Then you can mix in practically any amount of any other gas (so long as it’s not poisonous) into the mix and breathe it. On Earth oxygen is diluted about 4:1 with nitrogen. Noble gases such as argon, helium, and xenon are sometime added to artificial atmospheres since they have little to no biological effect.
So long as humans are provided a minimum partial pressure of oxygen of 150, it doesn’t really matter how high the other gases’ partial pressures get. Suppose you pumped in enough nitrogen (without displacing the air already present) to raise total pressure to a crushing 10 atmospheres (7600 torr, 1000 kpa). Now the oxygen would be diluted down to about 2%. But it’s breathable because oxygen is still present at 150 torr. Respiration should be normal.
As @hiphiphopflipflapflop pointed out, Venus has almost exactly the same gravity as Earth, but a much higher surface pressures (90 atmospheres!). I don’t think there need be any connection between gravity and pressure at the surface, though we can calculate how pressure drops with altitude above the surface.
Atmospheric pressure is the result of what’s in the atmosphere, how much there is (how tall/high), and the gravity of the planet in question.
As noted Venus has gravity similar to Earth, but because it’s atmosphere is heavy (e.g. a lot of ammonia) and there is a lot of it (from geological activity) the pressure there is huge.
@Mr_Paradox The chart on this page shows that none of the other inner planets besides Earth, has much magnetic field to speak of, including Mars.
The outer planets do have strong magnetic fields because they also have electrically conducting fluids at their cores.
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