When we send rovers like Perseverance to study the rocks of Mars...which ones can tell us the most? We're joined by NASA's Dr. Katie Stack Morgan, the Deputy Project Scientist for the Mars 2020 mission which includes Perseverance, to find out what the rover hopes to discover on the red planet.

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ERIC: The newest explorer on Mars, the Perseverance rover, touched down in February of this year, and now has six months of experience on the red planet. The Museum of Science hosted a virtual party, so we could take questions while watching the landing live and discuss what the mission hopes to accomplish by studying Martian geology. And we got a question from a young viewer: which Mars rocks are best? I think the answer depends on what you're looking for. But I thought I'd go to an expert, anyway. My guest today is Dr. Katie Stack Morgan, a geologist and the Deputy Project Scientist for the Mars 2020 mission that features the Perseverance rover. Katie, thanks so much for calling in from California and JPL.

KATIE: Thanks, I'm so glad to be here today.

ERIC: So straight to the point, Katie, which Mars rocks are best?

KATIE: All of them. It's hard not to say that because I'm a geologist and I study rocks on Mars. And there is something to learn something, exciting to learn about almost any rock that you would find on the surface of Mars. But it is a great question because we have to make decisions about where to study on Mars, where to send our rovers. And so that is a question that we have asked ourselves and we are asking ourselves every day on the surface with the Perseverance rover.

ERIC: Sending the Perseverance rover to this location, does this have particularly good rocks compared to where we've been in the past?

KATIE: Yes, it does. And so once you get into it, you can start to make distinctions between good rocks and better rocks. And the great thing about Jezero crater, which is the landing site for the Perseverance rover, is that it has rocks that represent a lot of different environments in which the rocks were formed. So we have an impact crater. And then inside that impact crater, we have rocks that were deposited in a lake, and by rivers, and so you can think about watery environments that might be really well suited to hosting life - ancient life on Mars. But also, we're interested in learning more about Mars as a planet and how Mars evolved through time, from its formation to the present day. And so we're looking for lots of different types of rocks. And so one special thing about Jezero is that it may also have volcanic rocks or rocks produced by volcanoes or deep in the Earth's crust. And so when you put all those rocks together in one place, that's when you have a really special spot. And that's why Jezero was chosen as the landing site for Perseverance.

ERIC: So it sounds like the best rocks are the rocks that have had the most stuff happen to them, because they hold the most clues to what was going on on Mars in the past. And that's really where all the missions goals go through. To find out what the conditions were like a long time ago, if there was maybe life a long time ago. I mean, a crater filled with water, we can tell all of that just by looking at the rocks.

KATIE: Yes, and I'll add too that one of the important things that's really fun to think about when you think about Mars rocks, and where to send a mission, is you want to make sure that you have all those rocks accessible to the spacecraft. So you have to have all of those different types of rocks in a small enough area that a rover can actually study that and reach those different places during its lifetime. And so, here in Jezero crater, we have a diversity of rocks in a relatively small area, and Perseverance has started to explore those rocks. The first thing that we are doing is we're exploring the rocks of the crater floor. So we don't necessarily think that this is the absolute bottom of the impact crater. This is the fill - the rocks that filled the crater and are now exposed on a relatively flat plane. And so we're trying to understand: are these rocks sedimentary deposited by wind or water? Or are these rocks volcanic? They could be lava flows, or they could be ash deposits blown out of a volcano. And so we are asking ourselves that question. In a way though, the good thing about this mission is that it doesn't really matter right now, because either of those options would be incredibly interesting. And one of the big goals of Perseverance is to collect samples that will be brought back to Earth by a future mission. And so it's the job of the Perseverance rover and the science team who operates the rover to select the best rocks to put into a collection that will come back to Earth. And what we know, and this is a great problem to have, is that we are interested in both sedimentary rocks and volcanic rocks. And they each have good things about them that will tell us more about Mars and about the potential for life on Mars. So you really can't go wrong, no matter what these rocks turned out to be.

ERIC: And you mentioned that sample return which is so cool to be able to hold some of these samples in your hand on Earth and use the instruments there, because the rover is really limited in what it can do, right? I mean without a human there, without the massive equipment, the rover can only do so much. And so the gold standard would be: bring it back, just like we brought the moon rocks back. And 50 years later, we're still studying them. So these Mars samples would be pretty priceless, right?

KATIE: That's right. And that's not to take away from the incredible science instruments that we are able to send to another planet. I mean, it's just incredible to think about the kinds of instruments we send now where we take instruments that otherwise would be in a lab and are very sensitive. We make them very small, and we send them through launch and landing, vibrate them, and they survive in the Martian conditions. But you're right, I mean, these instruments are not as sensitive, or necessarily as capable as the full instrumentation we have here on Earth to study rocks in labs. And so while we can make some interpretations about the rocks, and the potential that these rocks had life, on the surface of Mars with our rovers, we really think that we need to get those samples back into the lab here on Earth, to really make definitive statements about whether life once existed on Mars. And to learn about how the planet changed over time. There are just measurements we can't make on the surface right now.

ERIC: And mentioning that surface, a lot of the rocks are kind of laying around, you can see them. you can drive over to them with the rover, but the very surface is super old. On Mars, there is wind, and there's radiation. But some of those clues are sometimes buried just beneath the surface. And so perseverance has just started drilling, is that right?

KATIE: That's right, we attempted our first sample collection where we drilled a hole into the surface of Mars a couple centimeters deep, and we were looking to collect our first core. What we learned about that effort was that it went through the full process exactly as it was supposed to. But we didn't quite finish it off, we didn't quite get a rock core. So we're going to try again in the near future. And we're excited to do that. But Mars always throws curveballs. And this was this was one of them. And so we are excited to try again, to get our first rock core into that collection to come back to Earth.

ERIC: So what kind of results are you hoping, in your wildest dreams? What would you find out about Mars from this mission that we've never found out before?

KATIE: Well, of course, the big question we all want to know the answer to is: was there ever life on ancient Mars? And so Perseverance is looking for signs of ancient life: biosignatures. I think in my wildest dreams, I could imagine that we find something that is so different and compelling, compared to what you'd expect without life being there, that we say yes, that is a potential biosignature. And we have examples from rocks here on Earth, of the types of things we might look for. And generally, when we think about ancient life on Mars, we're thinking about ancient microbial life. And so there are very characteristic textures and patterns, that microbial life leaves in the rock record here on Earth. And so we'd be looking for exactly that type of thing on Mars, particularly in our settings, where we think we once had a lot of water, and we had a lake. And so that in my wildest, not so wild dreams, perhaps, would envision that we find a rock outcrop that has evidence for past microbial life in it.

ERIC: That's so fun. I mean, to think we're finally here, after all this time of studying Mars and thinking about whether it could have had life to think that this could be the robot that finds rocks that have evidence of aliens, and...doesn't it just give you goosebumps?

KATIE: It does. But one of the most exciting things about this mission, and just the Mars sample return effort, is that the rover has its part to play. But it really is the scientists back on Earth, potentially 10 years from now. And so these are people who are maybe, you know, children right now, are going to be the graduate students who make these discoveries. And so this is an effort that spans across generations. And that's one of the things that's really exciting about Mars sample return. And so we have our part to play right now with Perseverance. But we have to make that handoff to the next generation of scientists who will really answer these questions when the samples come back.

ERIC: So what's the kind of timeline for getting these samples back? So the rover's kind of collecting them as it goes, and then what happens to them between the time it kind of has its arms full of great rocks, and then the time they get back to Earth?

KATIE: Yeah, so the architecture for Mars sample return, how the missions will work and how the follow-on missions will work, is still in development. So this is still something that NASA is working on with its international partners, like ESA, the European Space Agency. But right now the thought is that the follow-on mission would arrive at Mars sometime maybe in the late 2020s, early 2030s, and would have a lander as well as a fetch rover that might be able to go and pick up the samples that Perseverance has collected. Alternatively, maybe Perseverance is still going in which case perseverance could play a role in delivering its own samples to the next leg.

ERIC: That would be cool.

KATIE: And doing that baton pass, or maybe a baton pass with 30 batons. And then from there, the samples would be blasted off the surface of Mars and would rendezvous with an orbiter. The next launch opportunities are really in the late 2020s, 2030s. And so, early 2030 is about when we could optimistically, I think, hope to get these samples back.

ERIC: That'd be so exciting to be able to open up a tube on the earth and have actual robot-collected rocks from Mars that could tell us more than we've ever found out before. It's just awesome.

KATIE: Yeah, it's really exciting.

ERIC: To wrap up, I think I'd just ask: why do you think it's so important that we explore Mars and keep making these discoveries?

KATIE: Yeah, I think we have some really fundamental, basic questions to answer about life and ourselves. I mean, life as we know it, that's us. And that's here on planet Earth. And I think we've always asked the question, and we continue to ask the question: are we alone? Are we it for life, and Mars offers the best opportunity in our solar system to search for signs of ancient life, even perhaps better than our own ancient Earth rock record. And so it's really important to step outside, I think, our own existence, our own everyday lives, which are busy and hectic and crazy, and thinking about these big, big questions. And to think about, you know, what is our place in the universe? And our neighboring planet offers the potential to answer that for us, at least in the context of our solar system. And, you know, if we find signs of ancient life on Mars, I think that really opens the door for thinking about life elsewhere in the universe, and its potential. And so that is just such a fundamental question that we can ask about ourselves, even though we're looking elsewhere and beyond. And so I think it's just really important to engage that part of our brains and to have that kind of imaginative thinking that then turns into scientific reality. And it's really important to participate in that and to think about that, and to contribute to that process. It's what makes humans special and different compared to other creatures here on Earth, that we can ask those questions and answer them.

ERIC: Well Katie, thank you so much for taking the time to answer our question and best of luck to you and the whole Perseverance team, from all of us at the Museum of Science. We can't wait to see what you'll discover.

KATIE: Thank you so much for having me.

ERIC: You can follow the Museum of Science, NASA, and even the Perseverance rover itself on Twitter for the latest updates on its Mars journey. Don't forget to send your questions to sciencequestions@mos.org. We just might feature them in a future episode. Until next time, keep asking questions.

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