(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.
Like Jupiter and Saturn, Neptune is one of the 'gas giant' planets, composed of a deep atmosphere around a liquid surface and sometimes a solid core. Its atmosphere consists of mostly hydrogen and helium, but up to three percent of its atmosphere is made up of methane, which gives the planet its striking blue colour. There are several cloud features, the most prominent being the great dark spot, a huge storm system which is as big as the Earth.