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Meteorites reveal Mars’ watery past -

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Robyn Williams: Meanwhile there are other movies of the cosmos being taken out west in Australia, in a video tracking system to spot falling meteorites. We reported on this a while ago in The Science Show. It's a scheme run in tandem with the Natural History Museum in London, and here's Caroline Smith who is surrounded by meteorites in her office in South Kensington.

Caroline Smith: Yes, we are working still in collaboration with colleagues actually at Curtin University and the Western Australian Museum on the Desert Fireball Network, which has been a really, really successful project.

Robyn Williams: Not only do you know when the meteorites have come down, you are one step ahead of the people who want to plunder them instead.

Caroline Smith: Certainly we have a good idea of where they've landed, we can go and look for them, and obviously, as I'm sure your listeners are aware, it's actually illegal to take meteorites out of Western Australia without export permits, so we do tend to be able to get in there maybe before plunderers, but I don't like that word very much.

Robyn Williams: No, but they need to be sensible of the fact that they are so valuable to science. They could have come from almost anywhere. You got a whole range of meteorites on display. Where do such large ones come from?

Caroline Smith: Most of the meteorites that we have on Earth are from the asteroid belt, so well over 99% of all of the meteorites that have ever been recovered on Earth, and they come in three main types; the stony meteorites, which are the most common ones, then we have stony iron meteorites, these are a mixture of iron and nickel metal and mineral grains, and then we have the iron meteorites which are made mostly of iron and nickel metal with maybe about a few little bits and bobs of other stuff in there, things like carbon and sulphur.

Robyn Williams: Do you get any large lumps coming from Mars?

Caroline Smith: We do get large lumps coming from Mars, but I suppose it's the definition of what is large. We've actually got one of the largest Martian meteorite fragments in any public institution in the world here at the museum. It's currently on display in one of our galleries, so visitors can actually see it. It weighs 1.1 kilograms and it's a large fragment of a meteorite called Tissint which actually is our most recent visitor from Mars, it only landed in Morocco in July 2011, so it has only been on Earth just over two years, and it is an extremely exciting meteorite and we've been heavily researching it here at the museum and sending bits out to scientists all over the world so they can research it as well.

Robyn Williams: Have you looked at it using your new technique to find out what's in the middle?

Caroline Smith: Yes, we have actually got a really fantastic micro-CT scanner. Many people will have heard of CT scanners in hospitals, it's quite a standard diagnostic technique. You know, if ever you've had the misfortune to have a head injury or something like that. We are using similar technology but we are using much more powerful X-rays. We can actually put rock fragments in the beam of X-rays and we can get a 3-D model of what the rock type is inside, we can see the different minerals, we can see the different textures, the different compositions. So it's an absolutely fantastic technique to be able to study meteorites.

Robyn Williams: But isn't the inside the same as the outside?

Caroline Smith: Well no, this is the thing, the outside of the meteorite has been burnt as it has come through the atmosphere, so it's been smoothed off. It's got a melted crust. And also as well, as soon as any meteorite hits the atmosphere it is becoming contaminated by Earth stuff. That is one of the reasons why meteorites that are seen to fall, it's really, really good to get out there as soon as possible and actually collect that meteorite and get it into somewhere like a museum or university where you have a controlled environment where you can try and minimise any contamination from Earth's atmosphere or sitting around in the desert, for example. So no, they are not the same on the inside as they are on the outside.

What we would normally have to do with the meteorite to see what it is made of is break it open or cut it open with a saw, and that's a bit hit and miss actually because obviously it depends where you saw or where the meteorite breaks. So what we are doing with the CT scanner is we can actually see the internal structure without having to use these destructive techniques of breaking it open or sawing it open, and this is very, very important.

Robyn Williams: On your screen you actually have an example of this, and if I can describe it almost, the size of half the screen, and it's grey and you've got lighter bits spread throughout, little blotches, and it's rather busy on the inside. What are you actually showing there?

Caroline Smith: Yes, this is actually literally data that is hot off the press, I just processed at this data this morning. We collected the data, and you're right, so we've got quite a large image there. Just to give you an idea, the width of that rock is about two or three centimetres. So it's a sizable fragment of rock. And we've taken almost like a virtual cut about halfway through this rock, and the different shades of grey you can see are the different minerals that this is rock contains.

This is a meteorite called Nakhla, it's a Martian meteorite and it fell in Egypt in 1911, and what you can see there is that the lightest grey quite large crystals are a mineral called olivine. The mid-grey stuff is pyroxene which is another common mineral, and we think the darkest grey bits is in-between glassy material, it's a glassy mineral. And then the very light specks you can see are little grains of minerals, we call them oxides or sulphides.

Robyn Williams: What does that tell you about Mars?

Caroline Smith: Well, that's the thing. This meteorite has been quite heavily studied, so we know that this meteorite formed either at the bottom of a deep lava flow or possibly in a shallow magma chamber, so this is an igneous rock, this rock is actually formed from a melt and has crystallised down. So we can tell from that that Mars has had a volcanic history. There is another very interesting thing about this meteorite, and in fact if you can have a look…can you see the olivine grains, which are these lighter ones, can you see in some of them the darker…they look like cracks…

Robyn Williams: Yes, cracks or an eye.

Caroline Smith: Yes, we think those are probably in-filled fractures with a mineral called carbonate, the same sort of stuff that you get furring up your kettle or the element of your washing machine so your washing machine conks out. But that's very interesting because those carbonates…and there's also clay minerals in there…show that at some point in the past on Mars this rock was wet. Water flowed through this rock to actually make those carbonate and clay minerals, and that was an absolutely critical discovery made by a scientist here at the Natural History Museum studying this meteorite in the late 1970s, and that was the first conclusive evidence that liquid water had flowed on Mars. And this is one of our favourite meteorites here at the museum.

Robyn Williams: Now, imagine a different rock with a different history, not necessarily igneous, that it would have not necessarily have been heated up to a level where it would kill life. If you had a little bug in there that looked like a micro-organism, could you see it with this technique?

Caroline Smith: It's debatable whether we could see it with this technique, and there are two reasons for that. One is the resolution that we can achieve with the scanner. So the larger the specimen you put in, the lower the resolution is. If you put a very small specimen in you might be able to pick up very small stuff in the scale of a few microns, so a few thousandths of a millimetre.

Funnily enough we are working on a project with the European Space Agency to look at rocks to say, okay, what features can you see using different techniques. And this is actually to look at…we call it biohazard assessment. The logic here is that if you have something living in a rock, so it's going to live in a little fracture or a little gap, it needs somewhere to live, if there are no fractures, if that rock is completely solid, it's going to be difficult for life to be in there. So what we are doing is we're saying, well, if we have a rock where we can see fractures, spaces, then that might mean there could be life in there, that's when you would go and start using other techniques. So it's not necessarily looking for actual life itself, it's looking for the sort of environment where life could exist if it was there.

Robyn Williams: When you are not in your office, do you go out into the field, and where do you go to pick up these wonderful rocks?

Caroline Smith: Well, funnily enough, one of the places we go to do our fieldwork and to collect meteorites is the Nullarbor Desert in Western Australia, and I'm hoping also to go to the southern Australian part of the Nullarbor Desert. And in fact something that you may find interesting or not, I don't know, is the last time I went there was in 2010 and it was a rather frustrating trip, we were looking for one of the meteorites that had been predicted to land with the Desert Fireball Network, and we didn't find anything, but what we did find was only the second lunar meteorite ever found in Australia, and it's called Lynch 002. So if people Google Lynch 002 they'll be able to see some work that we've been doing on that. And in fact not only is it only the second meteorite from the Moon ever found in Australia, and in fact there's only about 100-odd lunar meteorites known throughout the world, it looks like it could be a unique lunar meteorite. So that's a really nice bit of pride for Western Australia, that they've got one of the most rare meteorites ever found.

Robyn Williams: Is it here or is it there still?

Caroline Smith: We have a piece of it here, but most of it is in the Western Australian Museum in Perth. So it just goes to show, you never know what you're going to come across on these field trips.

Robyn Williams: So put it down, Darren, that's not a stone, it's a piece of Moon. Dr Caroline Smith who is curator of meteorites at the Natural History Museum in London.