Why are the air molecules in our atmosphere not escaping into outer space?
The answer is gravity – the same force that keeps us anchored to Earth. Molecules in our atmosphere are constantly moving, spurred on by energizing sunlight. Some move quickly enough to escape the grip of Earth’s gravity. The escape velocity for planet Earth is a little over 11 kilometers per second – about 25 thousand miles an hour. If Earth were much less massive – say, as massive as Mars – gravity’s grip would be weaker. That’s one reason why Mars lost most of its original atmosphere.In the vicinity of our heavier Earth, where gravity is stronger than on Mars, not all particles are equally likely to escape. Light ones, like hydrogen and helium, typically move faster than heavier ones, like oxygen and nitrogen. The light atoms are more likely to reach escape velocity and escape to space. That’s why light molecules are rare in our atmosphere, in contrast to their abundance in the universe at large.
Molecules in our atmosphere are constantly moving, spurred on by energizing sunlight. Some move quickly enough to escape the grip of Earth’s gravity. The escape velocity for planet Earth is a little over 11 kilometers per second – about 25 thousand miles an hour. If Earth were much less massive – say, as massive as Mars – gravity’s grip would be weaker. That’s one reason why Mars lost most of its original atmosphere.In the vicinity of our heavier Earth, where gravity is stronger than on Mars, not all particles are equally likely to escape. Light ones, like hydrogen and helium, typically move faster than heavier ones, like oxygen and nitrogen. The light atoms are more likely to reach escape velocity and escape to space. That’s why light molecules are rare in our atmosphere, in contrast to their abundance in the universe at large.
