The Lunar Reconnaissance Orbiter is a NASA space probe that's been orbiting the Moon since June 23, 2009. On March 19 it will mark its 1000th day in orbit! To celebrate, NASA released this cool animation showing the history of the Moon:
According to current thinking, the Moon itself formed after a planet roughly the size of Mars slammed into the Earth at a glancing blow. This colossal impact threw billions of gigatons of debris into space. Some of that fell back onto Earth, and some formed a huge disk around the (now once again liquefied) planet. This material eventually coalesced to form the Moon. But the story wasn't done: with impact after impact, wave after wave of bombarding material shaped and reshaped the Moon's surface. The animation above is a bit fanciful - it has sound, of course, and it shows time as a variable that flows at different rates - but gives a lovely overview of the violent past of our satellite. I like how I could see various features forming, knowing eventually they would be the familiar sites (and sights) I see through my telescope eyepiece. It's a good reminder that the way we see things now is not the way they've always been, and that sometimes the forces that shape our current circumstances are not necessarily gentle or subtle.
[My congrats to everyone on the LRO team for 1000 days of amazing science! If you want to see more about LRO, I've written about it dozens of times, and you can also check the Related Posts below.]