06/08/2018

Curiosity Digs Up Clues To The Early Martian Environment

11:39 minutes

just a sliver of the surface of mars
This computer-generated view depicts part of Mars at the boundary between darkness and daylight, with an area including Gale Crater beginning to catch morning light. Credit: NASA/JPL-Caltech

Curiosity has been roaming the Martian surface for nearly six years sampling the environment for clues into whether the planet could have been habitable at one time. This week, scientists published a study in the journal Science that described organic molecules—building blocks for life—in mudstone near Gale Crater, a 3.5 billion-year-old dry lakebed. Another study measured methane in the Martian atmosphere that varied with the seasons. Astrobiologist Jennifer Eigenbrode, who is an author on those studies, discusses what this reveals about how ancient water and rock processes may have worked on the planet, and what the findings tells us about the possibility of life on the Red Planet.


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Segment Guests

Jennifer Eigenbrode

Jennifer Eigenbrode is an astrobiologist at NASA Goddard Space Flight Center in Greenbelt, Maryland.

Segment Transcript

IRA FLATOW: This is “Science Friday.” I’m Ira Flatow. A bit later in the hour, a tour behind the scenes of natural history museums, where sometimes, a whole new species is right under your nose in plain sight.

But first, new mysteries on Mars. You remember Curiosity, the rover, has been roaming the surface of Mars for six years now, collecting samples and sniffing out the atmosphere, trying to get a sense of what’s there? And the results have finally come in.

The samples contained organics and methane. Now, what caused them? Not signs of life, exactly, but indicators that maybe the environment was, at one time, ripe for the possibility of life, and also signs of how the planet worked nearly four billion years ago.

The news was reported in two studies in the journal Science. My next guest is author of one of those studies, Jennifer Eigenbrode is a astrobiologist at NASA Goddard Space Flight Center in Greenbelt, Maryland. Welcome to “Science Friday.”

JENNIFER EIGENBRODE: Yes, thank you for having me.

IRA FLATOW: It’s nice to have you. Now, we’ve been hunting for organics on Mars for a while, even since the Viking mission, right, back in the ’70s, but have always come up empty-handed? What’s the difference this time?

JENNIFER EIGENBRODE: Well, this time, we sent Curiosity rover to an ancient lake bed. Now, at the time when we were choosing where we were going to put it, we weren’t sure there was evidence of a lake there. But we had some indications from the orbiters, the spacecraft that are moving around the outside of the planet and looking down at the surface.

But we had an idea that maybe this is a good place to look. There might be some lake sediments there. And it was an ideal place for us to look for organics, based on everything that we know on Earth.

IRA FLATOW: Right. Now, organics are not going to be the definition that life exists or has existed on Mars, correct?

JENNIFER EIGENBRODE: That’s right. Organic molecules are essentially molecules that contain carbon, and they could contain other elements too, but they’re largely just carbon-based. And on Earth, a lot of the organic molecules that we have comes from life. On Mars, the organics that we came across could also be from life. We don’t know. Their presence is not evidence of life.

IRA FLATOW: But it might have been life.

JENNIFER EIGENBRODE: It might have been. There are two other possibilities. The organic matter could be formed from meteorites, which are falling in through the atmosphere and landing on the surface of Mars all the time, and that was probably continuous for the entire history of the planet. There’s also the possibility that the rocks themselves may have formed organic matter, and in which case, they would have been broken up into little pieces and brought into the lake by rivers.

IRA FLATOW: So if this could be so many different possibilities, what makes it an important finding?

JENNIFER EIGENBRODE: Well, because we are ultimately after the search for signatures of life. We want to know if Mars ever had organisms living on it. And when we think of it, we’re really thinking about small things like bacteria.

On our planet, on Earth, bacteria and similar small organisms really reigned the planet for over three billion years. And we think that on Mars, the environments were very similar to those on Earth more than four billion years ago. And if life started on Earth around that time, hey, perhaps life started on Mars, too. In which case, hey, it must be around somewhere. So we wanted to go look. This is ultimately what we’re after.

But to do that takes quite a few steps forward. A colleague of mine gave the analogy of, if you want to go search for gold, you just don’t go digging in your backyard. You have to do your research. You want to go look for things that tell you, hey, these are good places to go look.

Well, we did the follow the water. Finding places that have water are good places to go look for more information. Then we searched out places that might have all the ingredients that we expect of life, such as nutrients and energy sources and that water all together.

And now, we have found the organic matter, and the organic matter could be from life or it could be food for life. Either way, it is sort of the one thing that we can now hone in on to do a more detailed search for signatures of life.

IRA FLATOW: So you’ve checked all those boxes off, right?

JENNIFER EIGENBRODE: That’s right.

IRA FLATOW: What’s the next box you need to check off?

JENNIFER EIGENBRODE: We need to go look for the biosignatures.

IRA FLATOW: What does that mean?

JENNIFER EIGENBRODE: Well, so one of the really unique things about the latest discovery is that the type of chemistry that we unraveled from the data we get from our instruments tells us how the organic matter was preserved in the rocks. And we found that at the surface of Mars. Even though the rocks are billions of years old and they were buried for a long time, they eventually were– the rocks on top were eroded away, and the rover came along and tapped into those really old rocks that were now exposed.

They’re exposed to lots of radiation, and that radiation produces things like free radicals and oxidants. These are all things that break down organic matter. Despite all of those things working against us to destroy the organic matter we sought, we still found it, and we found it in one of the places that may be regarded as an unlikely place.

And what that means for us is that if we get away from that surface environment, if we get away from the radiation, perhaps we can find other organic material that is better preserved and still contains the signatures that we seek.

So one way of doing that is to drill deep, get away from the radiation at the surface. Another way to do it is to look for places that have recently been excavated, such as by erosion from wind or maybe an impact event.

IRA FLATOW: Is that on the agenda next?

JENNIFER EIGENBRODE: Yes, actually, the European Space Agency has an ExoMars rover that’s going to be launching in 2020. And it has a drill on it that’s going to go down two meters deep. Now, in comparison, the Curiosity rover only drills five centimeters. It’s a very big difference.

So the instruments onboard the ExoMars rover have the ability to detect some of the types of signatures that we might expect to be preserved.

IRA FLATOW: You said you were looking for biologics, if I recall. Would you find biologics a couple of feet, a couple of meters down?

JENNIFER EIGENBRODE: They could be preserved further down, yes.

IRA FLATOW: And what would a biologic be when you say biologics?

JENNIFER EIGENBRODE: Oh, well, when we’re thinking of life signatures, these are things that are sort of like the imprints that life leaves behind. When we think of a skeleton that is, we might have had dinosaur around on Earth or a big mammoth or something like that. And it leaves a skeleton behind, and we uncover that later. That’s what large animals and creatures do.

But when we’re talking about microorganisms, they leave behind chemical clues. And sometimes they even leave behind fossils, in terms of cells, and these are the types of things that we might look for.

IRA FLATOW: Wow. I’m just– you spun a good yarn there. Yeah, go ahead.

JENNIFER EIGENBRODE: We find these things in rocks of a similar age on Earth, at least around three billion years ago. So if we can find them on Earth, then we have a whole set of our own processes on our planet that break down organic matter. We don’t have all that radiation, but we have tons of other things that happen.

So just the likelihood of those being preserved on Earth are moderately good. I mean, we found some. So the chances of us finding them on Mars are, for all that we know right now, are equally as good.

IRA FLATOW: Wow. So that’s very helpful. Before I let you go, tell us about this methane discovery also in the few moments I have left.

JENNIFER EIGENBRODE: Yeah. So methane is a modern chemical that we find in the atmosphere. And there have been a set of observations that people have made using different instruments and different techniques. And so we had this idea that, hey, it seems like there’s methane there, and all with Curiosity on the ground and making sets of measurements over three Martian years, that’s six Earth years.

So we’ve repeated the measurements over and over and over again. And lo and behold, there is a pattern to how much we see in the atmosphere. And this is the stuff, like, it’s in the air, and the rover is actually sniffing it.

IRA FLATOW: And so what does it mean that we found it?

JENNIFER EIGENBRODE: Well, it’s not constant, and this was a huge surprise. We did not expect this. It’s still a mystery as to why. However, we now know that there is organic matter in the ground, and that organic matter has that carbon that could go through different types of processes and end up as methane seeping out of the ground and into the atmosphere. And perhaps there’s a process that’s changing when it releases the methane and when it doesn’t.

IRA FLATOW: So you have all the dots, but you haven’t connected them yet.

JENNIFER EIGENBRODE: That’s right. We need more information, we really do. And so hopefully, the next set of missions will help resolve some of that. We have the ExoMars rover that I mentioned. There’s also the NASA’s Mars 2020 rover, and hopefully, that one will cache the right samples to bring home through the Mars Sample Return campaign and will bring those samples into labs here on Earth some day and get to really dive in deep.

IRA FLATOW: You’ve been working on this a long time, haven’t you?

JENNIFER EIGENBRODE: Yes, I have.

IRA FLATOW: You’re very excited. Is it really like a little bit of a dream come true, where you’ve gotten this far?

JENNIFER EIGENBRODE: Oh, this is just the next step. We need to search for life on Mars. And particularly, the ancient life is really intriguing, because on Mars, we have rocks that are super old and that we don’t have on Earth. And if we can learn about whether or not life started on Mars and what that was like, perhaps we’ll learn a little bit more about how life started on Earth.

IRA FLATOW: So when do you stop holding your breath?

JENNIFER EIGENBRODE: [LAUGHS] I don’t know that I will.

IRA FLATOW: When is the European mission happening?

JENNIFER EIGENBRODE: They’re both happening in 2020, both the Mars 2020 and the ExoMars 2020, the Russians are calling them.

IRA FLATOW: And so the drilling will commence, and when might we get that magic moment coming back? How soon might we know?

JENNIFER EIGENBRODE: Oh, I imagine that’s going to be in 2021 or 2022. That’s about right.

IRA FLATOW: Promise to come back and talk about it?

JENNIFER EIGENBRODE: Sure. I’d be happy to.

IRA FLATOW: We’d be happy to have you. Jennifer Eigenbrode is an author on a study in journal Science about what was discovered on Mars. She’s a biologist at NASA Goddard Space Flight Center in storied Greenbelt, Maryland. Thanks. Thanks for taking time to be with us today. Have a good weekend.

JENNIFER EIGENBRODE: Thanks for having me.

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