Titans of Science: Sara Russell
PodcastsThe Naked ScientistsTitans of Science: Sara RussellFrom space rocks to OSIRIS-REx. . . 22 April 2025In this edition of The Naked Scientists, Titans of Science continues with planetary scientist charged. . .
PodcastsThe Naked ScientistsTitans of Science: Sara RussellFrom space rocks to OSIRIS-REx. . . 22 April 2025In this edition of The Naked Scientists, Titans of Science continues with planetary scientist charged with analysing rock samples brought in from outer space, Sara Russell…Sara Russell: How to become a planetary scientistSara Russell, NHMIn 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 - Sara Russell was born in Manchester in 1966. She attended Altrincham Grammar School for Girls in the city before she read natural sciences here at the University of Cambridge, where she specialised in earth sciences. Sarah then studied pre-solar grains in meteorites, we'll find out what those are in a little bit, under the stewardship of the great Colin Pillinger at the Open University, and from there she moved to the California Institute of Technology and the Smithsonian Institution before settling at the Natural History Museum in London in 1998. She participated in multiple expeditions to Antarctica to collect meteorite samples and she's also been heavily involved with NASA's OSIRIS-REx mission, which collected samples from the asteroid Bennu to provide insights into the early solar system. She has even got an asteroid named after her and she's joining me today at Queen's College in Cambridge. Welcome back to Cambridge. How did you end up as a space scientist? How did you get into it? Tell us about the path into the subject. Sara - I grew up obsessed with space missions. I would always watch them on TV. I loved looking at the exploration of the moon and of Mars growing up, but I thought I really wanted to be an astrophysicist. I loved physics at school, that was my favourite subject and I thought that I'd carry on doing physics throughout my career, but then I came here to Cambridge to do a natural sciences degree where you have to try out lots of different subjects and so I chose earth sciences sort of on a whim, but as soon as I went into the lectures I was really blown away by it. I didn't know anything about earth science before I came here and I didn't kind of appreciate that you can look at a rock and you can learn to almost read it like a book. It tells you where it came from, it tells you what history it's experienced and by studying rocks you can reconstruct this whole history of our planet. That absolutely blew me away. Chris - And it turned, what, an astrophysicist into an earth scientist?Sara - Yes, absolutely. I was absolutely hooked and the lecturers I had around me were all just so passionate about their subjects and they all really wanted to, I think they wanted to recruit all of the physicists actually, they wanted everyone to love it as much as they did. So this wasn't that long after the discovery of plate tectonics which had completely revolutionised our understanding of how our planet worked and so there was still so much to learn and it felt like a really kind of young and vibrant subject to study. Chris - How did that get you into space though? Because that's very much feet down here on the ground, but you work now at the Natural History Museum and how we first met was you were playing around bits of an asteroid from millions of miles away. Sara - Yes, that's right. So in my final year we had some lectures on meteorites. So meteorites are any natural extraterrestrial object that has made it to the surface of the earth and in particular we had a guest lecture from Colin Pillinger who had just moved from Cambridge to the Open University then and he gave a talk about pre-solar grains. So what he said in his lecture was basically this idea that we're all stardust. So the Big Bang formed the universe 13. 8 billion years ago, it produced only hydrogen and all the other elements around us that we need to make our planet and to make people and plants, to make rivers and oceans, they were all made by stars that kind of are big element processing factories that by doing nuclear fusion they make all sorts of other elements. And we actually see that inside some meteorites, we see little grains that formed around ancestor stars to ours and by looking at them in detail they can tell us exactly what that star was doing, what the exact nucleosynthetic processes were going on and exactly how we got to be in this planet made of all of these amazing elements. Chris - Presumably those grains were part of the cloud of gas and dust then that coalesced to form the sun and then the clutch of planets that we've got and the asteroids that you're now looking at. Sara - Yes absolutely. So the idea is our solar system formed from a big cloud of dust and gas that included this dust from old stars and the gases that they had produced when they were dying as well and this collapsed under its own gravity to form the sun and eventually the planets around it. So that's the very big picture idea of what happened but we can interrogate that and have a look in much more detail at exactly what happened by looking at meteorites because they date from the time when all of this was happening. So most meteorites are four and a half billion years old and they formed at this time when the sun was just forming and there was a dusty disk around it that the very first solids were starting to coalesce and just as we can use a rock on earth to tell us their story we can use meteorites to tell us the story of what the temperatures and pressures were like at that time and what the composition was like and just learn about how that process occurred. Chris - How do you date a meteorite? You've just said that some of them are four and a half billion years old so you can tell us about your expeditions you did in a minute to Antarctica to find them but when you do find one how do you know it's that old?Sara - Yes so you can find out how old a rock is using radioactive dating techniques. So some radioactive isotopes have half-lives that are similar to the age of the solar system. They have half-lives of a billion years or so and we can use these to look at how much of the daughter isotopes have built up in minerals and that tells us how old it is. So we can actually age these rocks often very very precisely to within a few million years or better. Chris - But how do you know how much was there to start with for you to have found it and said well one thing turned into another? How do you know how much was there in the first instance?Sara - We know that when the solar system first formed it almost completely homogenized so all of the isotopes got really kind of mixed up so each element ended up with about the same proportion of isotopes most of the time with a few exceptions but because we then know what the original isotope ratio was we can work out how that's evolved over time. Chris - Did that lecture from Colin Pillinger, we're talking about the late great Colin Pillinger, he created the Beagle 2 mission that went to Mars. It was found more recently wasn't it? It went AWOL and luckily was found. That presumably captured you because you became his student. Sara - I did, I actually went up to him at the end of his lecture and asked if he was recruiting and luckily he said yes and I ended up doing a PhD with him in the very subject that he'd just given the lecture about. Sara Russell: Hunting meteorites in AntarcticaSara Russell, NHMIn 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.