Has anyone ever actually calculated the gravity required for a planet to keep an atmosphere

Can someone provide a link?

I'm constantly running into statements to the effect that Mars was too small to hang on to its atmosphere, and that's why it's (nearly) airless today.

I've been looking at photos of Mars, and from some of the big flattened plains areas, something BIG clearly gave it a whack at least at one point, if not more than once. Could the missing atmosphere actually be the result of cosmic cataclysms, and not from slow loss due to too weak a gravitational field? Venus is a little smaller than Earth, although granted not as small as Mars, and it has one HELL of an atmosphere.

Has anyone actually calculated what the gravity strength needed would be for a rocky Earth-class planet to hold on to an atmosphere?

"If it can't be expressed in numbers it ain't science." -- Anonymous

Someting to keep in mind is that since Titan and Ganymede are farther away from the sun than Mars, the temperature of the atmosphere is less meaning the average velocity of the molecules are slower. Mars has less than twice the escape velocity of Titan, for example, but more than twice the surface temperature so you'd think that Titan should be able to hold a thicker atmosphere than Mars.

You might want to look at this site.

http://www.astronomynotes.com/solarsys/s…

Of course they have. It's a simple question of escape velocity and the average speed of a gas molecule in the atmosphere. It's been shown that as long as they escape velocity is greater than ten times the average speed of a molecule, a planet or moon can hold an atmosphere. This is a simple calculation done by most students in an introductory astronomy class.

There's plenty of evidence that Mars once had water oceans which sloshed around. My theory is that it was once a moon of a much larger planet, which probably broke up to form the asteroid belt. If you look at the planets in this solar system, they are all more heavily cratered on one side, as if a shotgun blast went through and hit them all when they had one side turned toward the source.