Dr. Michael Meyer has been the lead scientist for NASA's Mars Exploration Program for over 25 years. He tells us what exciting things are coming up in our quest to understand the Red Planet.

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ERIC: From the Museum of Science in Boston, this is Pulsar, a podcast where we search for answers to the grandest questions we've ever gotten from our visitors. I'm your host, Eric, and we're kicking off our 2023 Mars Spotlight this week at the museum. We've got a life-size model of the Perseverance rover, a 20-foot Mars globe, and tons of programming and activities all throughout the summer. We get questions about Mars all the time from visitors. And we've answered many already here on the podcast. Most of them have focused on the newest rover, Perseverance, which has been exploring Mars since February of 2021. Today, we're focusing on the big picture, and the main question Perseverance is trying to answer. Scientists are trying very hard to find out if there was ever life on Mars. But why is it so important to search for that life? Who better to answer that question than Dr. Michael Meyer, the Lead Scientist for NASA's Mars Exploration Program for the last 25 years. Dr. Meyer, thanks so much for joining me on Pulsar.

MICHAEL: This is a real pleasure. And in fact, I enjoy every opportunity I have to talk about Mars.

ERIC: That's what we get a lot! Anybody who's working on something like this is so passionate about it, and it always comes through. So why don't we start with, you're the lead Mars scientist. What does Mars science actually mean? What does that encompass?

MICHAEL: Well, we have a neighboring planet called Mars. And you know, frankly, we don't know that much about it. Because, you know, for the longest time, it was a red dot in the sky that moved in funny directions. That's why they called it a planet. And it's only recently, in the last 50 years, that we've been able to start sending missions to that planet. And as you might imagine, as our instrumentation gets more sophisticated, you know, the capabilities of the orbiters and landers get better, and instrumentation is better. But also, as we learn more, we are gaining information. But it's very much like looking at a pretty picture through a toilet paper roll, where all you're seeing is a little bit of it. And it's really hard to put it all together until you gradually build up the information that that you need to make one hole picture as opposed to individual interesting sights.

ERIC: So you mentioned that we've been doing this for about 50 years, sending missions there. That both seems like a really long time that we've been able to do it, and seems like no time at all. In the history of science, we've only been, exploring Mars up close for that little amount of time. And you've been doing it for 25 years. So what are the biggest differences that you've seen in the last couple of decades? How has the technology allowed us to explore more? What was really the difference between 2022 and the late 1990s?

MICHAEL: As we learn more, we certainly have developed the capability. Most of the information we have about Mars has been from orbiters, you know, things that take pictures from basically 300 miles away from the surface, sometimes in different colors, so you get an idea of what minerals might be there. And of course, that capability has gotten more and more sophisticated, and the resolutions better. So you can see smaller features. And what that does is it has painted Mars as a very diverse looking planet. But looking at something and understanding what it is are two different things. And so it's not just looking at, you know, judging the book by its cover, but actually getting on the surface and exploring. And so one of the real things that has happened, that has really moved us forward, is putting mobile instruments on the surface. We have rovers on Mars that can go different places. And now it can pick up that rock that is part of a formation that you saw from orbit. And now you can actually figure out what it really is, as opposed to something that kind of matches pictures that you've seen before of other things that you recognize on Earth. So our understanding at the smaller scale is vastly improved. And we've made some major progress. When we started the modern age of Mars exploration, you know, at the turn of the century, we weren't whether or not Mars was just interesting because of its geology. We weren't sure of its history, whether or not it had water in its distant past. But we had features that were intriguing that would let us know, yeah, this is a good thing to look.

ERIC: A lot of good questions to ask.

MICHAEL: Good questions, and big questions. And one of them was. okay. Was there ever water on the surface of Mars? Because that, in our viewpoint, that's what you need for life. Was there ever water on a surface of Mars? Well, we think maybe, probably. And so with the missions that we've done, we've now concluded, yes, not only was it on the surface of Mars, we know that it had been there for long periods of time. Long enough to form minerals that only form in water, but also long enough that it has the potential for having been a place for the origin of life. And so now we're at that stage where we go: Mars had water on its surface. Mars could have supported life. Did it happen? Is it there? So now we've narrowed down our search to asking some very specific questions about certain features, like, oh, that is a river delta, water flowing into a lake. If life existed at that time, that place ought to have evidence. And that's where we're looking with Perseverance.

ERIC: Talking about every mission building on the ones before it, we're now not just looking from Earth, we're not looking from orbit, we're not even just looking from the surface, because Perseverance is going to be the first step in bringing some of those samples back to Earth. Can you talk about why we would want to bring some of those samples back to Earth, instead of just having Perseverance do science on them?

MICHAEL: Yeah, if you can imagine you go camping, and you find some interesting rocks. You have a little magnifying glass that you can look with and go yeah, this is interesting. But you have no idea what the rock is. I mean, the instruments on the rover are little bit better. But it can only carry so many instruments. And the instruments only have a certain capability because it has to fit on the rover and has to travel through space and survive the whole journey. It has to send data back. Get that sample, bring it home, you will know what that is. You'll know what it is to an extreme degree. And you can use any instrument on Earth to do the measurement you need on that particular rock to tell you what is. So that's one part of it. The other thing of bringing samples back is that you can now look at your samples grain by grain. Many rocks, if you cut them and look at them in thin sections, you can see all these different grains next to each other, that make up that rock. It's a very complex organization. And what rock is next to each other is important. When you bring a sample back, you can cut that open, you could look at each of the grains. Each grain is like looking at a whole new rock. You could do everything you want to it. And now you get a whole picture of the entire lifetime of this rock in terms of when it originally formed, what things might have been incorporated into it, what the whole region where it was formed is like, so you get the chapter to a book when you get a rock and are able to examine it page by page.

ERIC: So this will really help us answer the question - we know there were great conditions for life on Mars, but did life exist? We'll be able to say, we found some evidence that has to come from life.

MICHAEL: It's complicated. It's a little more challenging than that. Because you might find something that, let's say, on Earth, life makes something that looks like that. But that doesn't mean it can't be made by a different process. You know, shells or something that looks smooth on the outside or, you know, has a certain pattern.

ERIC: There's lots of things that are made by not-life-processes that look like life.

MICHAEL: And we're talking about different planet. So there may be a process that we don't quite understand that forms something that we haven't seen before. But that doesn't necessarily mean that it's evidence of life. We can also look at organic matter, which is something we're all familiar with, because that's what we are, right? Well, functioning organic matter, right? But if we find complex organic compounds in samples from Mars, then that would be a really good clue that maybe life had gotten started on Mars, or maybe almost got started on Mars. There's a lot to learn. And this is at a very, very fine scale. We're talking about measuring individual molecules, something that we can't do with the rovers.

ERIC: So you've been pondering life elsewhere in the solar system, and particularly on Mars, for a really long time. How do you usually respond when people just ask you: was there life on Mars?

MICHAEL: I get the question of like, what are the odds? I have no idea! It's a good question. Because we know that it's at least possible. There's a couple of things that play into this. One is the same time that life started on Earth, there's water on Mars, so it happened here, it could have happened there in that same timeframe. So this is very encouraging. Was was water around long enough for it to start? We don't know how life starts. We don't have good evidence. Here on Earth, our record has been erased. Plate tectonics, life itself, rain, erosion, you know, all these things have done their best to make sure that what was going on the first billion years of Earth's history has been largely erased, and certainly evidence of how life got started, or even what the earliest life was like, is absent or highly controversial. On Mars, if anything like that happened or even got almost there, Mars is ancient. Its rocks on the surface are ancient. We could go and walk on the surface of Mars and pick up a 3 billion year old rock. And we have it in hand. And by looking at that we could tell what was going on on Mars. Did life ever get started? It will be a challenge.

ERIC: We know that the conditions were right, a long time ago, we are looking for evidence of that life. Is there any chance there could be life on Mars today?

MICHAEL: Well we don't see anything on the surface of Mars. Mars looks like a dry desert, it looks pretty lifeless. On the surface, liquid water can't exist. So it's not a great environment for life. So we don't expect to find it on the surface, even if it does exist on Mars. But the subsurface, that's a different story. The subsurface, if you go deep enough, you have the possibility of liquid water. You have temperatures that are in the right range to support complex organic chemistry, you have the potential for something living in the aquifers on Mars. Now, we don't know if there's aquifers there, there's good reason to think there might be. So there's a lot of things, a lot of potential habitats for life, even today, that we don't have direct evidence for. We have theory that says it's a good chance to be there. And if we have some evidence that says life started on Mars, then it's worth the effort and expense to go into the deep subsurface, to look for evidence of life on Mars.

ERIC: So we've been asking this question for a really long time. What would it mean if we found evidence that life started on Mars? And for a long time, it's been theoretical, and now we're getting to the point where we could actually start thinking about it. So what do you think it would mean, just to science in general?

MICHAEL: Finding evidence of life on Mars, the first thing is, you do the happy dance. I mean, this is the brass ring on the merry-go-round. This is winning the lottery. This is fantastic. And there's a couple of major things of import about finding evidence of life on Mars. One is it now looks like life is easier than we might have thought. There's only two planets in our solar system that look like they could support life. And they both have life? Okay, well, maybe every time you have the right conditions, you get life started. And now all sudden life looks easier. It means that now, the universe is teeming with places where there's life, right? So that's number one. Number two, life that we know on Earth is amazingly self-similar. We all have the same DNA, RNA, proteins, metabolic complexes. We all have the same functional organic chemistry. And everything you look at, you know, the bacteria on up to the elephant, essentially, has the same cellular machinery. So I suspect we have a very myopic, narrow view of what life is like. Everything on this earth is like us. We don't have two different systems. So finding evidence of life somewhere else means that now you can study a different life. And that might be the eye opener into understanding what life really is, as opposed to the phenomenology that we have of what we see of life here on this planet.

ERIC: Well, it'll be exciting to see what develops over the next couple decades. Dr. Meyer, thanks so much for joining me here on Pulsar.

MICHAEL: Well, thank you. Appreciate it.

ERIC: You can keep up with all of the latest Mars exploration updates at mars.nasa.gov. And be sure to check out all of the Museum of Science offerings online and in our exhibit halls by visiting mos.org/mars after April 15th. Until next time, keep asking questions.

If you liked this episode, be sure to check out:
What's a Typical Day Like for a Mars Rover?
Which Mars Rocks Are Best?
Mars Helicopter? Really?
Who Gets to Drive the Mars Rover?
How Do You Land a Robot on Mars?

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