Why doesn’t the atmosphere (air we breathe) just float off into space?
Some objects in space have atmospheres like Earth and Jupiter. Others like asteroids and the moon don’t have an atmosphere.
Why doesn’t earth atmosphere just drift away into space?
What am I missing about the concept of atmosphere?
In: Planetary Science
Gravity. Air has weight.
Molecules of atmosphere need the same velocity anything else would to escape a gravity well. For Earth this is about 11km/s. It’s rare for Nitrogen or Oxygen to be moving that fast at the temperatures you see in the upper atmosphere, so it just falls back down.
Lighter gases have higher velocity at the same temperature,(higher velocity at the same kinetic energy), so it’s easier for those to reach escape velocity. Gas giants have much higher gravity, so they can hold on to things like Helium and elemental Hydrogen.
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