Continuing with the space theme, we have a TPL Kids visitor who wondered: Why can we breathe on earth but not in space?
We're able to breathe on earth because the atmosphere is a mixture of gases, with the thickest gases nearest the earth's surface, giving us the oxygen we need to breathe.
In space, there is very little breathable oxygen. A ground—based experiment by an experimental astrophysicist at Syracuse University found that oxygen atoms cling tightly to stardust. This prevents the oxygen atoms from joining together to form oxygen molecules.
That's why astronauts need to wear a spacesuit when they are outside the spacecraft. Their spacesuits are outfitted with a backpack called the Primary Life Support Subsystem that provides breathable oxygen.