Sara Russell: Hunting meteorites in Antarctica

In this edition of Titans of Science, Chris Smith chats with a planetary scientist charged with analysing rock samples brought in from outer space, Sara Russell…

Chris - And it was during that time that you went to Antarctica to look for meteorites then?

Sara - Yeah it's over the next few years that I went on several meteorite collecting expeditions so meteorites land pretty much anywhere in the world but there are certain parts of the world where if they land they will survive better and they just accumulate over time and so the two great places to look for meteorites are hot deserts where they won't rust away and the very best place to look for meteorites is Antarctica because that's also a desert. It's also a big deep freeze so it's fantastic for preserving meteorites and the glaciers tend to move the meteorites around and can dump them in certain areas so they actually get concentrated in certain places to make them easier to go and collect.

Chris - How big are they?

Sara - They are all sizes so extraterrestrial material is falling all around us Chris so I think maybe up to 40,000 tons a year of material is falling to earth every year but nearly all of that is in the form of dust and then as you get to bigger sizes they get rarer and rarer so the meteorites that we pick up in Antarctica they tend to be from the size of a nut to an apple maybe that's that would be the typical size.

Chris - Do you find them by flying over the ice and spotting them or have you got other crafty ways of seeing them because, I mean, Antarctica's huge you can't just go for a wander around Antarctica to go and find them, or do you?

Sara - Yes we do. Honestly it's the most fun you can ever have it's like a big easter egg hunt but yes because the glaciers can sometimes hit into a mountainside and then the ice will start to ablate away or be removed away by the wind and any rock that's inside the glacier gets dumped in certain places so they do get quite concentrated to such an extent that you can go down around either by foot or we use skidoos as well to drive around the ice.

Chris - I can see the attraction now.

Sara - Yeah so fun. Cold but fun.

Chris - How many did you find then?

Sara - So there are expeditions that go every year and they will typically find a few hundred to a thousand on each trip.

Chris - Goodness. And they come back or they go back to host laboratories like the one you run now I presume. How do you interrogate them? What do you do once you find a nice meteorite that's 4.5 billion years old? What do you do with it?

Sara - We classify it is the first thing that we do and broadly they can be made of iron or stone or sometimes a mixture of iron and stone so there's that very simple classification but then what we really want to know is where it came from so one of the problems with studying meteorites is that unlike a terrestrial rock that you might have gone out and done some field work and collected yourself so you know exactly where it's from we rarely know where they come from so it takes quite a lot of work including looking at its mineralogy looking at its bulk chemistry sometimes looking at its isotope composition to work out firstly broadly where it came from. So most meteorites come from asteroids but a few come from Mars and a few come from the moon so we want to find out which of those categories it's in or maybe it doesn't look like it comes from any of those categories and then we want to work out for the asteroidal ones whether it originated from the innermost part of the solar system or the outermost part of the solar system where there was more ice around originally.

Chris - How do you know which of those it is?

Sara - For the icy ones they often still contain water which is trapped inside clay minerals so that's one of the things that we look out for we look to see if it has clay in it or it may have completely dehydrated but we still see evidence that it was once there by looking at its texture and composition.

Chris - When you look at something like that and you think I've got something here that's probably four and a half billion years old I know when I find fossils on earth it sends a shiver down my spine because I think I'm looking at something that in this case probably a few hundred million years old at most but when you've got something that ancient it must create a sort of a special frisson for you.

Sara - Absolutely. So for me I love every meteorite that I look at each one is a little bit different and I think each one can tell us something new about our origins about how the planet's got to be here how we got to be here and so absolutely I get excited with every meteorite that I look at it never gets boring.

Chris - How did you end up at the Natural History Museum?

Sara - Yes so there are not very many places that you can work on meteorites around the world but the Natural History Museum in London is one of them it has one of the oldest meteorite collections in the world and it has a fantastic and very comprehensive collection of meteorites as well as having a fantastic suite of labs that look at the mineralogy and chemistry of rocks so it was a really kind of attractive place for me to go to be able to kind of pursue these research interests that I have.

Chris - It's slightly a strange question but it's just occurred to me that how did people back in history know that a meteorite was something special and not just another lump of rock?

Sara - Yeah that's a really good question so for a long time people didn't really believe that meteorites existed and during the Enlightenment in the 1700s for example when people were starting to try to get more rational about science there's actually the the intelligentsia at the time thought that meteorites couldn't possibly exist there couldn't be rocks from space even though there were lots of folk stories about it and it was only around 1800 that scientists started looking at these rocks that peasants had claimed to have seen falling in the fields and realised they were all quite similar to each other that the penny dropped that actually they really were extraterrestrial rocks.