# Why does helium-3 stay in the moon and not escape from it?

So the moon is full of helium-3.

Since it's a gas in the moon's vacuum... Why doesn't it escape?

• Can you provide a reference for your claim? – casey Jun 26 '14 at 22:59
• InquilineKea is not in the habit of putting a lot of effort into questions. Rather, of putting a little effort into lot of questions. – naught101 Jul 9 '14 at 13:42

The quantity $q(t)$ of in a cubic meter of lunar regolith is thus dictated by a simple differential equation, $\dot q(t) = \alpha(t) - \beta(T)q(t)$. Time averaging the bombardment and escape rates yields $\dot {\bar q}(t) = \bar{\alpha} - \beta(\bar T)q(t)$. This differential equation yields a steady state value of $\bar q = \bar{\alpha}/\beta(\bar T)$.