Moons of our Solar System
Moons of our Solar System

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Moons of our Solar System

2 Our Moon and its craters

Galileo discovered lunar craters in the 1600s but the debate about how they were formed was resolved only in the 20th century. Learn how different crater shapes and sizes come about, and have a go at classifying real Moon craters.

In this video Christine Shupla and Paul Schenk introduce you to the Moon, the craters upon it and the evidence for ancient volcanism. Christine concludes by speculating that pieces of rock that ‘blew off early Earth’ might one day be found on the Moon. By this, she means chunks of ejecta thrown out by large impacts onto the Earth (of the same size as those that formed the Moon’s oldest craters), and which ended up on the Moon. No rock older than 3.8 billion years has survived on Earth, so finding older Earth rocks on the Moon opens a very important window into our own planet’s past.

Download this video clip.Video player: moons_1_vid020.mp4
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My favourite moon does have to be our Moon, the Earth’s Moon. It does not always appear terribly exotic, but, in fact, it’s much more mysterious than people give it credit for. We did not see the back side of the Moon until we sent spacecraft around it. The back side of the Moon is very different from the front side. The front side has these big, dark blotches on it, and the back side doesn’t. It’s heavily cratered, it has a thicker crust, and we still don’t understand why.
When you’re looking at the Moon, you see these big, large, round areas - these big, large, round spots. Some people might call it the Man in the Moon, or if you’ve looked at the rabbit in the Moon. Those tend to be basins that were giant, enormous impacts early on in the Moon’s history.
An impact crater forms when a comet or an asteroid of any size strikes another planet. And it usually does so at several kilometres per second, which is an extremely high velocity, which creates an explosion. And impact craters are very interesting in the fact that they do that excavation. They bring material that was deep - that we could never have seen otherwise - and actually blasts it out and throws it out onto the surface.
When you first look at the Moon with binoculars, you could see many craters very clearly. And some of them have bright rays extending in all directions. Tycho is one of the most famous craters on the Moon, and it is pretty far to the south. It is way down here. This particular creator has very bright rays that extend from it, and so you can see Tycho without binoculars. And we also have Aristarchus. Aristarchus, for the scientists, is very famous because around this area there’s a fair amount of volcanic activity. And so they’re looking at things like a lava tubes and channels and little, itsy-bitsy volcanoes - which is just incredible to think that there used to be volcanoes erupting on our Moon. It has little volcanic glass that spewed out from cracks in the Moon. Our Moon has information about the early parts of our Solar System and how we formed. And some day maybe we will go to the Moon and find a chunk that blew off of early Earth. And that would be amazingly incredible. And that’s the only place in our Solar System that we are likely to be able to go and find a piece of early Earth.
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