What is the Moon made of?

14 July 2014

Interview with

Sara Russell, Natural History Museum

This week marks the 45th anniversary of the launch of Apollo 11, the mission that The_moonfirst set mankind on the moon. Since that first landing, a total of 12 people have now walked on the moon at 6 different landing sites. Together they have travelled nearly 100km across the lunar surface, and deployed over two tonnes of scientific equipment.

But one of the greatest legacies of these Apollo missions is the 383 kilos of moon rock that the astronauts lugged back to Earth.

Britain's only moon rock is stored at London's Natural History Museum, and Graihagh Jackson joined Professor Sara Russell there to take a closer look ...

Sara - When I was a child, I remember the Apollo mission. At the time, my friends got excited about almost everything, but this is the first time I'd seen my parents and other adults looking genuinely amazed and excited about what was happening, and that made me really think this is something so special.

Graihagh - And in front of us is one of those samples from one of those lunar missions. Can you tell me a bit about how this rock came to be here?

Sara - The president at the time, President Nixon, actually gave a small piece of moon rock to every country around the world.

Graihagh - Just looking at it, it's about thumbnail size and it's encased in a big glass marble. The rock itself is actually quite black, but I always thought the moon looked quite grey. So, why is it so black?

Sara - Yes, so if you look up to the moon in the sky, you can see most of it is a white colour and it's white because it's made mostly of one mineral called anorthite. It's thought that when the moon first formed, it was entirely molten and then as bits started to crystallise, the lighter crystals floated to the top and they happened to be white. But also, if you look up at the moon, you can see it's got big dark blotches on it. And these, we think formed by later volcanism. So, it could be that this rock is a piece of this later volcanic activity on the moon.

Graihagh - So, what have the lunar samples told us?

Sara - The lunar samples have told us so much about the moon. Before the Apollo missions, we had no idea how the moon formed, so there were lots of different theories. One theory was that it could've co-accreted with the Earth so they could be kind of twin planets, or it could have spun off the Earth if the Earth was spinning really fast, or it could be an asteroid that the Earth had captured. Really, there were loads of theories floating out there and it was only after people have brought rocks back that a consensus emerged that actually, the moon formed by - this story that's even more amazing than any of those, which is that there was a giant impact of this Mars-size body into the early Earth then material was splattered off which then accreted to form the moon which was very hot to start with and then cooled down slowly.

Graihagh - I believe you've done some work yourself specifically on some lunar samples as well and it's all to do with water.

Sara - Actually in the early days, when the material was brought back from Apollo, the scientists remarked on how dry it seemed. But now, 45 years on, we've discovered that actually, instead of being bone dry, the moon actually did contain water. We can see evidence for that in little minerals called apatite and then at the Open University, my student Jessica Barnes has looked at the isotopic composition of the water to try and determine exactly where it came from. If you look at the very primitive samples, actually, the water looks very similar to the Earth. We think the sources of water on the moon and on the Earth are probably actually asteroids and also micrometeorites that are continuously bombarding the Earth and the moon especially in the early history of the Solar System.

Graihagh - Does that mean there's no water there now or could there be some water locked away?

Sara - Yes. Well, as well as our work on the solid samples that we have here on Earth, people have been using spacecraft in orbit around the moon to look at the presence of water. There are places on the poles of the moon that stay cold all the time. We think now that these areas might actually have water ice. So, it looks like actually the moon might be a fairly good source of water which could be exploited for example if there's ever a lunar base.

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