The Moon has clearly seen some stuff.  It’s visibly heavily cratered across it’s surface, which has remained unchanged since it’s surface solidified 4.2 Billion years ago.  Think about that – the Moon has been the same, with the exception of cratering, for 4 Billion years. This is a stark contrast to the Earth, whose erosion and tectonic activity cause the crust to change on scales of a few hundred million years. Astronomers have worked hard to learn about the early solar system by looking at the Moon and its cratering patterns.  Most of the visible craters on the Moon are...