Sending a piece of Mars home

Why are we sending a Mars rock back to Mars?
14 July 2020

Interview with 

Caroline Smith, Natural History Museum London


Astronauts need faster spacecraft, better radiation protection and heat shields before they can enjoy the Martian landscape in person.


Now, if all goes well, NASA will soon be sending a new rover - called Perseverance - to Mars too. It’s car-sized, weighs about a tonne, is powered by a plutonium thermoelectric generator and it even has its own drone - called the Mars Helicopter - that will test the feasibility of flight on Mars. Like the Rosalind Franklin ExoMars rover, the overall mission is to seek out signs of ancient life, and it will also collect and store rock and soil samples for return to Earth in the future. But also aboard is something quite unusual: it will be taking with it a little piece of Mars that landed here in the past. And to explain why they’re doing that, Chris Smith was joined by Caroline Smith, principal curator of meteorites at the Natural History Museum in London...

Caroline - I know it sounds a bit strange, doesn't it? Well, it's actually a really interesting piece of scientific research we're doing. It's actually going to be very important for one of the instruments that I'm actually involved with, which is called Sherlock. And what we've actually done is we've taken a small piece of one of our Martian meteorites, which has a name in Arabic. So you'll have to forgive my bad pronunciation, but it's so are you Hermia zero, zero eight or we call it SAU008. You have to sort of think about saying it and it was found in Oman in 1999. And the reason why we've selected it is that it's actually on something called the calibration target for the Sherlock instrument. And so what that does is when the instrument is operating on Mars, so doing the analyses of different rocks and different minerals within those rocks, but also really importantly, Sherlock is looking for the presence of organic molecules where you, what you can actually do is before you use the instrument to do an analysis on Mars, you actually test how the instrument is working, using the calibration target. And there are other, other pieces of material and other things on the calibration target, but the Martian meteorite is one of the, one of the things on there.

Chris - Caroline, it may sound like an obvious question, but how do you know that the meteorite you have sitting there from Oman is from Mars at all?

Caroline - No, it's a great question, but it says to us - to a geochemist, it says Mars, it has moles written through it like a stick of Blackpool rock has Blackpool written for it. So it's got lots of different chemical signatures in its makeup, in its minerals that show that it has to be from Mars. So there was lots of pieces of evidence pointing towards these meteorites being from Mars, but it was only in the mid 1980s that it was conclusively proven that this type of meteorite was from Mars. And that was done by being able to detect tiny amounts of trapped gases in the minerals. And those gases get trapped in the minerals, in the rock, because that rock is actually cooling because it's a, it's a volcanic rock, it's an igneous rock. And we were able to take out or measure those tiny, tiny amounts of gas using very sophisticated instruments. And when the composition of the gas was compared to the composition of the Martian atmosphere, and we know what Mars' atmosphere is originally from the Viking landers, they didn't move around; they just landed in the late 1970s. And there's been further experiments since on different rovers and different missions. We know exactly what Mars' atmosphere is like. And the little bits of trapped gas within these meteorites have got exactly the same composition as the Martian atmosphere. So that says to us, that is, you know, there's nowhere else that those rocks can be from, they have to be from Mars.

Chris - Why can't you do this calibration of the instrument here and just send it calibrated?

Caroline - Well, we can. And, and we do. And a lot of work has been done by my colleagues at JPL who have designed and built this instrument to do exactly that. So JPL actually have a mirror copy of the instrument in the lab over in Pasadena. And they also have a small piece of the meteorite over there to test the lab based instrument. But it's basically, it's good scientific method when you're doing analyses. You want to be measuring the calibration target, the standard material every time that you do an analysis to make sure that your instrument is working as you expect it. So you can be confident that the data you receive back from the rover of the Martian material that it's measuring as it's roving around Mars is actually good data and sending you back reliable and accurate numbers.

Chris - And how have you picked where you're going to sample them and what are you actually going to measure?

Caroline - It's a very complicated thing. So we know where we're going on Mars now it's a place called Jezero crater. It has lots of different rock types, but importantly it has rock types that we think could well have been laid down in water or altered by water. And water is a very important thing that you need for life. So if you've had water somewhere, that's a good indicator that you could have had the conditions for life. The rover has a number of different pieces of payload, so different scientific instruments on there to measure different things. And so you're looking for different rock types, their textures, their sort of physical form. And you look at the chemistry and you use the different instruments to have a look at the different minerals that are there, the shapes that are there, the different chemistry of those different minerals to see what's what, so that's what we'll be doing. We're using Sherlock in combination with a number of other instruments on the rover to actually really try and get a good idea of what those rocks are and do they show any evidence for past life or the evidence that maybe the right chemistry, the right environment was, was there for past life.

Chris - I mentioned when we began talking that one of the aspirations of perseverance the rover is that it will collect some samples and store them for possible later retrieval back to earth. Um, how on earth are you going to get them back?

Caroline - Well, it's a very challenging scientific and engineering thing to do actually. It's going to be one of the most complicated missions since the Apollo missions in the late sixties and early seventies. So it's a multi-phase mission. It's an international campaign. We actually call it the Mars sample return campaign. And it's being done jointly between NASA and the European space agency. And so there will be different missions sent subsequent to perseverance collecting the samples. And then the last one of those will actually blast those samples off the surface of Mars. The samples will be collected in another satellite for want of a better word that's been orbiting from Mars, waiting for those samples to be delivered to it up in space. And then hopefully we'll be able to safely get those samples back on earth in around maybe 2031-2030ish. That's the sort of timeline we're looking at. So, you know, 10, 11 years from now, we'll hopefully get these really precious, amazing samples back. Because we can only answer these questions once we get the samples back on earth.


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