Thanks. My point is that our star is very well behaved and our magnetic field is quite reliable. Probably a combination of both.

I just googled and found that Venus has no magnetic field today. So I guess our star is pretty well behaved, and Venus has sone good gravity.

I’ve always thought that if the momentum / velocity of a gaseous molecule is greater than the escape velocity of the planet… bye bye gas! No H2 or He in earth’s atmosphere because at ‘earth temperature’ that gas just can’t remain captured by earth’s gravity.

But I don’t know if that’s an actual thing b/c I never researched it or did the math. It’s just a theory.

And slamming charged particles into a planet’s atmosphere at relativistic speeds is surely also a contributing factor to removing an atmosphere. - just to bring the conversation back on topic.