Why doesn't the atmosphere vanish into space?(대기가 날아가버리지 않는 이유)

<written on 2018.10.28>

The space is very close to a vacuum. It has nearly nothing that's not a part of a celestial object, like Earth. Imagine a vacuum cleaner, which works by sucking dust from the floor. That's right! Vacuums have a characteristic in common: sucking objects. But actually, a vacuum doesn't 'suck' objects. It is just an extreme case when the density of matter in and outside a container is different. 

https://www.universetoday.com/141560/did-you-know-the-earths-atmosphere-extends-beyond-the-orbit-of-the-moon/

So the space is a vacuum, and the Earth is not. Why doesn't the Earth's atmoshere just scatter into the space, unlike how vacuum cleaners suck in air? The reason is that the atmosphere doesn't just abruptly end at an edge. Instead, as it is shown in the graph above, the density of air gradually decreases, and so does the air pressure at each height. As a result, near the border of the atmosphere, its density and air pressure is so low that it isn't much different to the near vacuum of space.

 

cover image: theconversation.com/breathable-atmosphere-may-be-more-common-in-the-universe-than-we-first-thought-128648