Molecular Weight Retained

[ajtribick]

Programs like StarGen output the minimum molecular weight retained in a planet's atmosphere. I'm just wondering how this is calculated, and whether hot-Neptunes such as Mu Arae d could hold on to hydrogen/helium atmospheres.

[bdm]

I believe it is a function that depends on the gravity of the planet and the temperature of the planet's atmosphere. Higher gravity and lower temperature facilitate the retention of lower molecular masses.

The source code for Stargen may also be available online. If so, you could inspect it and find the formula in the source.

[Hamiltonian]

Programs like StarGen output the minimum molecular weight retained in a planet's atmosphere. I'm just wondering how this is calculated, and whether hot-Neptunes such as Mu Arae d could hold on to hydrogen/helium atmospheres.

Here's another old thread that has the information:
http://www.shatters.net/forum/viewtopic.php?t=3275