Before going into work this morning I was watching coverage of the space walk where the guy was about to fix the belly of the shuttle. Somehow the conversation got around to welding in space. The main point being they just didn’t know the effects of welding in a vacuum.
All the while there was a live shot from the shuttle looking down upon the planet. Then I started thinking, a vacuum, in essence, will suck in any material not in a vacuum. (Well, you know what I mean).
So what I wonder is, what holds an atmosphere in place around a planet? Why isn’t it just whisked away into the void? I could understand if there were a physical shell made of titanium or something, but it’s just gas. What keeps it all together?
Now, I realize an exact answer will probably read like the dissertation of an MIT grad, but I’m hoping to glean enough to have a basic understanding of this. I’m almost certain it has mostly to do with gravity, but again, we’re talking about gasses.