I was asked two questions a few weeks ago and I’ve been pondering the answers ever since: Why is there no air on the Moon? And how does our air stay on Earth?
These fantastic questions got me thinking about my answers to What is air made of? and Why are there no trees on the Moon?. But neither of those quite answered these new questions. So, after much deliberation, here’s my answer!
The planet Earth is surrounded by something called an ‘atmosphere’. An atmosphere is the name scientists give to the gases that surround a planet (or a similar body, like a moon). The Earth’s atmosphere is mostly made up of nitrogen, oxygen and water vapour. I wrote about the Earth’s atmosphere in my answer to How high is the sky?.
The gases in an atmosphere are held in place next to that planet or moon by something called ‘gravity‘. Gravity is what keeps things together in space – like stars and planets. It’s also the reason that things fall back down to the ground when you throw them up into the air. Gravity keeps us from falling off the Earth and it keeps the Earth orbiting around the Sun. We can’t see it or smell it or taste it and we can’t really feel it, even though it’s pressing us onto the Earth’s surface all the time!
So gravity keeps the gases in the Earth’s atmopshere next to our planet and stops them from disappearing off into space.
The Moon has a very thin atmosphere, which is made up of different gases to the atmosphere on Earth. It isn’t made of the gases in air, so when astronauts visit the Moon, they have to take air with them so that they can breathe!
If you enjoyed this post, you might also like to read How bright does the Moon shine?
And, once again, I’d like to thank my friend Alex for permission to use his amazing Moon photo in this post.