Thread: Atmospheric retention

Can a planet with 60% earths radius retain carbon dioxide, oxygen, nitrogen and water in its atmopshere at 300 K?

Probably not for long. Most at risk would be loosing the water/hydrogen. Some depends on what you mean by "retain." If you mean a few million years---sure. If you mean a billion years, well that's another matter.

i was just interested because they say mars lost its atmosphere in about 1 billion years. So i would assume this would be longer? By retain i mean keep its atmosphere at those temperatures.

I am not sure the planet's temperature has a large effect the upper atmosphere (near space) is normally cold.
There seems to be several possible contributing factors.
Strength of solar wind at planet's distance from star.
Planet's magnetic field providing shielding from solar wind.

Consider Titan orbiting Saturn with a mass of only 1.3 x 10²³ kg but retains a thick atmosphere.
(Mars 6.41 x 10²³ kg)

True titans atmoshere is thicker than earths.

Ok lets assume this planet is somewhere between Earth and Mars and has a magnetic field although maybe half the strength of earths. I always thought that the thermosphere was the hottest part? Then again venuses thermosophere is colder than earths even though its closer to the sun. Lets say the atmosphere is 1.2 bar at this point.

Originally Posted by KTevolved

Can a planet with 60% earths radius retain carbon dioxide, oxygen, nitrogen and water in its atmosphere at 300 K?

Of course it's not just the radius of the Earth but its density that determines its mass and atmospheric holding power. Also its temperature range is important so that it would need to rotate something like the Earth and Mars to keep the maximum temperature down. Carbon dioxide is a heavy gas so it would not be a problem for Earth-like temperatures. For a planet with 60% the gravity of Earth, other gases such as water (steam), oxygen, and nitrogen would also probably be present if they were present in the planets formation but would probably be in lesser percentages. Oxygen was accordingly a minor atmospheric gas on Earth before life broke down carbon dioxide. Nitrogen is relatively heavy and inert therefore would be a likely gas in such an atmosphere. Hydrogen, helium and methane would escape more easily from such a planet. Like Venus and Mars, I would expect to see carbon dioxide as the major part of the atmosphere, along with sulfur dioxide and ammonia maybe abundant in the atmosphere. If it had large oceans then ammonia and sulpher dioxide would be less common in its atmosphere and clouds of water more abundant.