Science Interviews


Mon, 14th Jul 2014

Should we mine the Moon?

David Rothery, the Open University

Listen Now    Download as mp3 from the show Returning to the Moon: Apollo 45 years on

The Apollo samples allowed scientists to understand just how rich and diverse the EarthriseMoon geology is. But these samples have only (literally!) scratched the surface and now the race is on to get back to the moon.

Unlike the so-called ĎSpace Raceí of the 1960s between Russia and America, today many more countries are competing, including China, Iran, Japan and India as well as a host of private companies. But what are they all racing for?

Chris Smith spoke to David Rothery from the Open University...

Chris - What actually do we understand about the moonís origins?

David - Well, Sara was talking about what we call the ĎGiant Impact Theoryí for the lunar origin and that emerged in the first decade after Apollo, where if you look at the isotopic composition, the oxygen isotopes and so on, of lunar and terrestrial material, it looks like they're formed from the same stuff. So, this theory arose that there was a collision, a body like the Earth, a body may be Mars size. They were both differentiated and they had iron rich cores and rocky outer layers. They're on their way to being planets, but they bumped into each other and thatís the last stage of planetary growth. The core of the incoming body carried on and joined the Earthís core, but the rocky outer part of both - parts of it was fragmented and thrown to orbit around the Earth and re-accreted into this hot body which was molten, as Sara said, there was magma or ocean and the first forming crystals rose to the surface to give us these pale and anorthite-rich lunar highlands. The moon almost lacks an iron core because all the iron from the original body joined the Earthís core. So, thatís why the Earth and moon are different in composition, but isotopically, they're so similar. It looks like they're formed from the same stuff. The best idea is this giant impact which is being challenged lately. Itís not done and dusted. It might be wrong.

Chris - When you say the isotopic composition, in other words, the flavours of chemicals that we find here on Earthís surface are such an exquisitely close match for what's on the moon that it sort of hints that one coming from the other, they're both made of the same stuff.

David - There are three different flavours of oxygen, they look so similar. But recently, itís been pointed out, actually, they're not absolutely identical so maybe this giant impact theory has some flaws in it.

Chris - But what do those lunar samples tell us the moon is made of? What's up there that may be of use to us now or in the future?

David - Geologically, the moon is nowhere near as diverse as the Earth. If you have a lot of water in a planet, you can have a lot of geology going on - melting from granite and concentrate ore minerals, and so on. That hasnít happened on the moon, although there maybe some traces of water, itís very small beer really.

So geologically, the moon is perhaps less diverse - you're not going to go to the moon and form a gold rush. But the one thing on the moon that you might want to bring back to the Earth is something called helium 3 which doesnít even belong to the moon, itís come from the solar winds Ė helium nuclei streaming out from the sun that get splatted into a lunar soil and just held there. It doesnít make it to the Earthís surface because of our atmosphere and our magnetic field. Helium 3, you could use as a source of clean nuclear energy. You can fuse helium 3 with heavy hydrogen and get cheap nuclear power. Itís never yet been proved, that it can be done economically. But if it can be, then fetching helium 3 from the moon to the Earth would be a way to do it. But it costs money to get stuff from one planetary body to another. If you want to use the moonís resources, you're better off Ė I would say, using them to do things on the moon or in space. It costs a lot to get out from the Earth into orbit, so get stuff from the moon to use in space.

Chris - Here on Earth, weíre acquainted and familiar with the concept of mining. We generally find areas which are in enriched in certain minerals and we dig there to get them out. Would we see a similar sort of structure on the moon, or is it distributed all over the moon and so, it would be very difficult to have a mine for whether itís helium 3 or some other thing we wanted?

David - Helium 3 would be pretty uniformly distributed. Most mines on the Earth, weíve had water circulating through the crust, concentrating stuff into places which makes it economical to dig a tunnel to get to it. Thatís unlikely to happen on the moon. With the one exception thatís come to my attention is sites where a metal-rich asteroid might have formed a crater on the moon. These metal-rich asteroids carry platinum group elements, platinum, palladium, iridium, and so on. If you can find that asteroidal material in or around a crater, you might want to go mining for it. But mostly I suspect is scavenging across the lunar surface.

Chris - So, the bottom line is that, whilst there may well be things up there the cost of recovering it to Earth is likely to be pretty preclusive and therefore, would it be better to say that itís more likely we would want to use it in situ? Weíd want to establish some kind of operation on the moon and use it there.

David - I think we are going to want operations on the moon and itíll be very important for the economics of doing anything on the moon that we can use as many of our local resources as possible because to lift stuff off the Earth to the moon is very, very expensive. We need a cheap way of getting to the moon and back.

Chris - Do we know where the resources are? Has anyone done a sort of mapping exercise of the moon to spot which the juicy bits are to make a beeline for?

David - Well, everywhere on the moon is regolith, padded rock which you can make habitats out of and shield yourself from radiation. There are craters near the poles which never receive sunlight which do have water in them. Itís not the same water that may have been with the moon when it formed. Itís water thatís arrived with comets hitting the moon. Most of the water when a comet hits is vaporised and the molecules will bounce around. If they hit a hot surface, theyíll bounce again. If they go to a cold surface like a shadow inside a crater where it's -150 centigrade, they will stick there. If that crater is at the poles so the sunlight never peers over the crater rim, the floor will be at 150 degrees permanently and the water molecule will stick there. And there is 5% ice thatís been proven now inside some polar craters. If you went to lunar base and want to provide water for astronauts to drink or for use in industrial processing or to make into rocket fuel, you get it from inside these polar permanently shadowed craters. Thatís the one resource thatís been located in concentration, water.


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