Thread: Can a earth mass planet have a much heavier atmosphere?

I assume that its easier for more massive planets to have a dense and massive atmosphere, and that the less massive a planet gets the more likely the gas will escape into space.

Is earth sufficiently massive to hold on to an atmosphere with double the amounts of gases in our atmosphere? If it were possible would that be the equivalent of going in a hyperbaric chamber like they have for some types of medical treatments?


Different question. If a string of ice comets totaling about half the mass of the moon had collided with the early earth formation when most of the surface was molten, what would that much more water do? Would the current time frame surface of the earth be completely covered with oceans?

Originally Posted by icewendigo

I assume that its easier for more massive planets to have a dense and massive atmosphere, and that the less massive a planet gets the more likely the gas will escape into space.

Is earth sufficiently massive to hold on to an atmosphere with double the amounts of gases in our atmosphere?

Just look at Venus for an example. has roughly the same mass as the Earth, but a surface pressure 93 times of the Earth's.

Crap i should have thought of that, thanks. Do you have any idea what is the approximate level of pressure at which we start noticing a difference? I guess 93 times would crush us, but what about 2 times, would we notice it?And if the atmosphere was about double or triple the density, would this allow or make it easier for birds to fly while being much larger (ex twice or three times larger than a condor?)

Originally Posted by icewendigo

Crap i should have thought of that, thanks. Do you have any idea what is the approximate level of pressure at which we start noticing a difference? I guess 93 times would crush us, but what about 2 times, would we notice it?And if the atmosphere was about double or triple the density, would this allow or make it easier for birds to fly while being much larger (ex twice or three times larger than a condor?)

The actual record for human survival is 68 times normal pressure( in a hyperbolic chamber). Free divers have gone as deep as 273 meters, and since water pressure increases by about 1 atm every 10 m, they experience ~28 atm of pressure. 2 atm would be the equivalent of diving to a depth of 10 meters.

If we evolved on such a planet, we would obviously be able to tolerate it, but at present gass percentages with how we are now, some gasses would become poisonous at certain pressures afaik.

Originally Posted by KALSTER

If we evolved on such a planet, we would obviously be able to tolerate it, but at present gass percentages with how we are now, some gasses would become poisonous at certain pressures afaik.

Oxygen toxicity starts at about 0.5 atm, since the normal partial pressure is 0.21 atm, at 2.4 atm with present percentages, oxygen would be toxic. You can solve this by dropping the percentage of oxygen. However, other gases become narcotic at high pressure (nitrogen narcosis sets in between 4.5 atm.) To get to really high pressures, you would have to have a helium/oxygen atmosphere.

Would it be true that a very low mass planet could hold on to a thick atmosphere if the star it was orbiting had weak solar winds?

Maybe even something as small as the moon could hold a breathable atmosphere if it was orbiting a brown dwarf?

the atmosphere would have to be composed of denser gases to do what you say- S02,krypton,SF6 etc

I was more thinking of a 300 - 400 km deep atmosphere of oxygen nitrogen.

Originally Posted by Janus

Originally Posted by KALSTER

If we evolved on such a planet, we would obviously be able to tolerate it, but at present gass percentages with how we are now, some gasses would become poisonous at certain pressures afaik.

Oxygen toxicity starts at about 0.5 atm, since the normal partial pressure is 0.21 atm, at 2.4 atm with present percentages, oxygen would be toxic. You can solve this by dropping the percentage of oxygen. However, other gases become narcotic at high pressure (nitrogen narcosis sets in between 4.5 atm.) To get to really high pressures, you would have to have a helium/oxygen atmosphere.

A great example can be found in SCUBA diving. To go really deep we use Trimix or Hydreliox. Timix uses nitrogen with the helium-oxygen mix to avoid HPNS while Hydreliox uses hydrogen with the helium-oxygen mix. Basic Heliox can be used but the threat HPNS(High Pressure Nervous Syndrome) is high. It would probably be possible to survive in a high pressure atmosphere with such a mix however you run into concentrations of caustic chemicals in atmospheres like that of Venus. Speaking of high pressure atmosphere planets, is the reason for Venus' high surface temperature, in addition to its closer proximity to our sun, due to the dense atmosphere. Lead is molten on the surface if I remember correctly. If we were able to move Venus into our orbit but on the opposite side of the orbital path would that result in an atmosphere change... New thread

I think the point is, if we had evolved under such a high pressure atmosphere, It wouldn't be a problem. It would be our natural environment.

Im more wondering about environments from the perspective of what Types of planets could be noticabely different from earth while still allowing space travelers to live on it temporarily while not wearing astronaut suits.So double the current atm pressure (around 0.4?) is as about as good as it gets while staying safe for someone exiting a starship without a suit and exploring for a few hours? Is it easier for large flying creature(pterodactyl etc like) to fly in a planet with 0.4 atm and about 80% of earth gravity?

I would think avian species would have it a bit easier with lower gravity as for atmospheric density? It may help up to a point but then you are having to move a mass through something of a higher density.