The escaped our atmosphere bit is actually pretty advanced physics. Most kids would assume that the helium would form a spherical shell if they knew about gravity.
Well, people can happen on the right prediction for the wrong reasons. I'm sure I didn't know about thermal atmospheric escape when I thought this, or probably even that a gas at a temperature consisted of molecules with a random distribution of kinetic energies centered on that temperature. I think I just thought that there would always be stuff denser than helium that would push it further and further away from the earth, without limit. (This is almost true, but most of the solar system is filled with hydrogen, which is less dense than helium.)
reply