(The Moon is currently about 384,000 km or 60 Earth radii away from Earth, which is about fifteen times further away than it was when it first formed.) The Moon probably couldn't have formed closer than 3 Earth radii because tidal forces from the Earth would just pull it apart again, and it is unlikely that the impact could have ejected material ...
About 78% of Earthâs atmosphere is made up of nitrogen. Credit: NASA We might commonly think of Earth as having an oxygen-dominated atmosphere, but in reality the molecule makes up only a fifth of our air.
In the top one-fourth of the planet, the pressure and temperature are so high that the hydrogen atoms are stripped of their outer electrons, forming a liquid metal. Like Jupiter, Saturn has a thick atmosphere composed of hydrogen and helium. The ratio of hydrogen to helium ratio decreases with depth. Methane and ammonia are also present. The atmosphere of Saturn envelops a thick layer of metallic hydrogen. The atmosphere of Neptune consists mainly of hydrogen and helium, but about 2.5-3% of the atmosphere is methane. Like Uranus, clouds in Neptune's atmosphere are composed of crystals of methane. -=-=-=-=- Since gas giants do not actually have a surface, it is rather difficult to determine where their atmospheres end.