NASA Mars InSight Lander Principal Investigator Bruce Banerdt discusses the first mission dedicated to studying the deep interior of Mars.
Mars InSight, which landed in November 2018 to study the planet’s crust, mantle and core, has detected more than 1,300 marsquakes. Seismic waves have revealed the size, depth, and composition of Mars’ inner layers. The InSight mission is winding down as the solar-powered lander’s power supply continues to dwindle.
Managed by NASA’s Jet Propulsion Laboratory for the agency’s Science Mission Directorate, InSight is part of NASA’s Discovery Program managed by NASA’s Marshall Space Flight Center and is supported by several European partners.
In this episode of Small Steps, Giant Leaps, you’ll learn about:
- Meteoroid strikes on Mars
- InSight’s most amazing discoveries
- What happens when the mission ends
Bruce Banerdt is a Planetary Geophysicist at NASA’s Jet Propulsion Laboratory (JPL) and serves as Principal Investigator of the Mars InSight mission. Banerdt has worked in the JPL Earth and Space Sciences Division since 1977 and has participated in several planetary flight instrument teams, including the Mars Orbiter Laser Altimeter on Mars Observer and Mars Global Surveyor; the Synthetic Aperture-Radar on Magellan; and the Seismometer on the CNES NetLander mission. He served as Project Scientist for the Spirit and Opportunity rovers for six years. Banerdt has served on a number of NASA and National Academy of Sciences advisory panels on planetary and space science and has published over 75 journal articles, reports, and book chapters. His research focuses on the geological history of the planet Mars and geophysical investigations of the interiors of terrestrial planets using analyses of gravity, magnetic, topographic, and seismic data. Banerdt has a bachelor’s in physics and a doctorate in geophysics from the University of Southern California.
Bruce Banderdt: In many ways, this has been a charmed mission. Our cruise and our landing went flawlessly. The spacecraft has operated really, really well. Very, very few anomalies.
With our seismometer, we’re, in a way, looking at a brand new planet. And every discovery we make is groundbreaking because no one’s gone there before.
Deana Nunley (Host): Welcome to Small Steps, Giant Leaps, a NASA APPEL Knowledge Services podcast where we tap into project experiences to share best practices, lessons learned and novel ideas.
I’m Deana Nunley.
NASA’s InSight Mars lander, the first mission dedicated to studying the Red Planet’s deep interior, is gradually losing power and nearing the end of a mission that has achieved all of its primary science goals.
The Principal Investigator for the mission is Bruce Banerdt, and he joins us now. Bruce, thank you for taking time to talk with us.
Banerdt: It’s my pleasure.
Host: Let’s start with a quick overview of the Mars InSight mission, what makes it unique, and where we are in the timeline.
Banerdt: Well, InSight was the first mission that was conceived to concentrate on studying the deep interior of Mars. So we got lots of missions that look at the geology, that look at the atmosphere, the chemistry of the surface, even the magnetic field and solar wind interactions. But there’s never been a mission before that went to Mars to really look down below the surface, scratch the skin and delve down all the way down to the center of the planet to the core.
And so, I’ve always felt that this was sort of the remaining big hole in our understanding of Mars. We have a lot of information about the geology. We have a lot of information about the history, but the interior is really important in terms of really being behind all the geology on the surface, except for impacts, which is the one thing from the outside. And it also has a lot of information, what we think of as the fingerprints of the early formation of the planet. And so, we wanted to go to Mars and do our first investigation of the deep interior of the planet and fill up that last gaping hole in our basic understanding of the planet.
As to where we are in the mission right now, we landed about four years ago, almost four years to the day. We landed at the end of November 2018. We put down our seismometer a few months later. We tried to put down our heat flow probe, and that was unable to penetrate down to the depths that we wanted for interesting reasons having to do with the soil of Mars. But meanwhile, we’ve been listening with our seismometer. We’ve been taking data with our weather station, our magnetometer, and we’ve been tracking the spacecraft with the DSN to look at the wobble of the North Pole of Mars for four years. And by doing that, we’ve been able to delineate all the major divisions below the surface of the planet, the crust, the mantle, the core, and their size, something about their composition, and even something about their temperatures.
So at this point, we’re starting to wind down. The dust has covered our solar panels. We’re down to about less than 10 percent of the efficiency of the panels that we had at the beginning of the mission. We’re running our seismometer for about eight hours every third day or so, and then using the intervening days to try to get some more charge in the batteries. But even with that, the batteries are getting a little bit lower and a little bit lower all the time. And we feel that sometime in the next, somewhere between a few weeks to maybe a month or two, we’ll probably lose communication with the spacecraft.
Host: What are your primary focus areas as the mission winds down?
Banerdt: Well, what we’re focusing on right now is trying to squeeze every bit of science data we can out of this last phase of the mission. There’s some really good reasons to extend the time that we’re taking data, the seismic data. We’re just leaving right now the time of year when the background noise from all this atmospheric activity is covering up our marsquakes. Marsquakes are really small signals, so a little bit of wind, a little bit of atmospheric turbulence can just drown them out. But sometime in November, we expect that noise to collapse based on the last two Mars years. And then when that noise collapses, we can get down to the really, really quiet backgrounds that allow us to see these really small marsquake signals.
So, if we can take some more data for the next month or two, we can probably pick up another set of marsquakes that’ll allow us to refine our analysis even more. So, it’s on a week-by-week basis. We’re trying to figure out how we can get just a little bit more data, a little bit more data all the time. And actually, keeps us busy. So we don’t think too much about the end coming up on us.
Host: You’re talking about marsquakes. Could you give us an inside view from the perspective of principal investigator of what you’re looking for with marsquakes and what you’ve learned through this mission?
Banerdt: Well, marsquakes are really important for the simple reason is they act almost like, you can think of them as a flash bulb that lights up the inside of Mars. So, when a marsquake happens, when a fault breaks somewhere on Mars and starts shaking the planet, it sets up waves that travel through the planet, like sound waves. And so those sound waves, as they go through the planet, they bounce off of various different layers. They bounce off the bottom of the crust. They bounce off the core, and they also get refracted the same way light waves do as they go through different materials. And so, they’re picking up information as they go through the planet. And when we detect those waves with our seismometer, which is detecting the motions of the surface that are set up by these waves, we can analyze the shape of those waves and the character of those waves to pull out all this information that they’ve picked up as they’ve traveled through the planet. So, whenever a marsquake goes off somewhere, it’s like a little flash bulb going off and giving us a little view of another part of the deep part of Mars. So, that’s really the value of marsquakes for us.
Other people actually look at the marsquakes themselves, what we call the source parameters, and look at how the rocks are breaking, how the dynamics of that process works. And that tells people about things like what the forces that are set up in the crust, the direction and size of the forces that are squeezing the rocks. And that helps us understand the geology and the geological history of Mars. So, there’s lots of different aspects to the marsquakes, but for me, they’re mostly just big flash bulbs.
Host: What do you consider to be the most amazing InSight discoveries?
Banerdt: Well, there’s been so many of them. We went with some very, very specific goals. When you do a proposal to NASA for one of these missions, they want you to be really specific. They don’t select you if you say, ‘We’re going to go and do a lot of great stuff.’ NASA requires you to be really precise with your goals. They want you to know what you’re going to measure, how precisely you’re going to measure it, and what kind of questions you’ll be able to answer with that kind of precision. So we actually came up with about 10 different things that we were going to measure on Mars. Things like the thickness of the crust, the size of the core, the density of the core, what the distribution of marsquakes is around Mars, things like that. And so, we’ve actually been able to meet all of those goals. And so, that was, I wouldn’t say a surprise or anything, but it was definitely really gratifying to be able to actually make good on all of our promises in our proposal.
But we have discovered some things that were really unexpected. When we got a measurement of the size of the core, for example, we found out that it was quite a bit bigger than we had expected. So we thought it was going to be about 1,700 kilometers in radius, and actually it’s about 1,840. So 140 kilometers out of 1,800 is not that much, but scientifically, that’s a pretty big difference. And the reason is when you have a core that’s bigger than what we expected, that means its density has to be lower because we knew what the total mass was from gravity. So if you have a bigger core, the density goes down, the only way that you may get the density to go down is to mix in a bunch of things that are much lighter than iron, things like sulfur, and oxygen, maybe even hydrogen into the core.
So, there’s a lot more of that in the core than we thought. And right now, we don’t know how it could have gotten there. We have theories on how the core is formed and how much, say, sulfur can be dissolved in the material as it’s separating and raining down to the center of the planet. And right now, most of those theories can only get you about 12 percent, maybe it’s possibly 15 percent sulfur into the core, but our measurements require at least 15 percent and maybe even 20 percent sulfur. So that was a big surprise to us because it means there’s something wrong with our theories of core formation. So that’s kind of a big deal, and we’re still scratching our heads and pursuing a bunch of ideas on how to fix that.
The other really surprising thing was something that we just reported on. It was the observation of some really big craters that were formed on Mars. We actually saw some marsquakes. They were some of the larger marsquakes that we’ve seen during the whole mission, bigger than magnitude four. And we didn’t realize it at the time, but those were actually from a pair of meteoroid impacts. So, this was only figured out later when MRO, the Mars Reconnaissance Orbiter, took some photos in the area where our epicenters for these marsquakes were and found a pair of large craters on two different locations.
One was about 3,500 kilometers from our spacecraft. The other was about 7,500 kilometers from the spacecraft. And these craters, they’re huge by the standards of something that happens currently. They’re about 150 meters across. So that’s about the size of a high school football stadium. And we only expected to see a crater of that size form every, I don’t know, 20 to 40 years. So to see one is really, really lucky. And to see two was actually puzzling. We don’t know why we would see two within the space of a few months when, statistically, you wouldn’t even expect to see one except every few decades. So that was a big surprise, and it’s really, really a science bonanza for us because when you get a signal that is from a known location, that actually simplifies your processing enormously.
Generally, when we get a marsquake, we have to figure out where the location is by trying to analyze the waves. And that actually makes it harder to figure out other things because there’s tradeoffs between location and velocity and things like that. But if you know the exact location, then suddenly all the other things you’d like to learn from that wave become much more easily accessed, and they become much more precise. Plus, we were able to calibrate our location techniques.
Normally, on the Earth, you use lots and lots of different seismometers to triangulate the location of an earthquake. On Mars, we only have the one seismometer, so we have to use some fairly sophisticated techniques using polarization and things like that to figure out where the marsquakes are. And there’s some uncertainty in that. It’s not as precise a method as we use on the Earth. So we are really grateful to be able to use these impacts to be able to test that, test those techniques, and actually verify that they’re working pretty well.
Host: How has Mar’s InSight been able to make such impressive discoveries?
Banerdt: Well, I mean, honestly, one reason why it was able to make such impressive discoveries is because, like I said, there was this big gap in our knowledge. It’s easier to make impressive discoveries if no one has looked there before. So we looked in a place that no one has gotten around to looking before. It’s almost like going to a new planet. The surface of Mars is one planet, but once you get down more than a few kilometers, where you don’t have canyons exposing rocks, you can’t access it with a ground-penetrating radar, it’s a whole new planet down there that no one’s ever seen before. And so, with our seismometer, we’re, in a way, looking at a brand new planet. And every discovery we make is groundbreaking because no one’s gone there before. It’s just like we’re setting foot on a brand new planet for the first time and making those first measurements. Just like back in the ’70s and ’80s when Voyager went past Jupiter, Saturn, Uranus, and Neptune for the first time and opened those new worlds up.
Host: What do the discoveries about the internal structure of Mars say about the interiors of other rocky planets and exoplanets?
Banerdt: Well, the great thing about Mars, first of all, is that it retains a lot of the fingerprints of the early formation of itself. So the thickness of the crust, the size and the composition of the core, those are all things that were set up in the first few tens of millions of years of Mars’s formation. We don’t really have that information from the Earth. It’s mostly been destroyed by plate tectonics, by a really vigorously convecting mantle. And so, we have models of planetary formation that are based on what we do know about the Earth. It’s based on things that we’ve been able to deduce from the Moon, from return samples and from seismic measurements on the Moon.
But the Moon is a very different kind of a place. It’s a really small planet. If you go all the way to the center of the Moon, the pressures and temperatures are equivalent to something maybe 150 kilometers deep on the Earth. So you really don’t get the kinds of pressure and temperature conditions that most planets undergo as they’re formed. Mars is a really good laboratory that way because it’s big enough to have those kinds of conditions on the inside, but it’s small enough that it hasn’t gotten so carried away like the Earth did to destroy all that stuff.
So, as the theoreticians bring in the data that we have on Mars and start to test their models of formation using what we now know about the structure of Mars, they can then start to extrapolate that better to other planets. Instead of just having one data point for the Earth and another data point for the Moon, we now have a data point for Mars that allows them to better fine tune these models of planetary formation and differentiation.
Host: Bruce, what are significant challenges you and the team have faced with this mission?
Banerdt: Well, we’ve actually been really lucky. In many ways this has been a charmed mission. Our cruise and our landing went flawlessly. The spacecraft has operated really, really well. Very, very few anomalies. Our biggest challenge, I guess, was the mole. We have this mole that was supposed to hammer itself down into the Martian crust, into the Martian soil. We were trying to go down three meters, five meters to get down into the soil. And we were going to be able to measure the heat flow from the planet by looking at the very small temperature gradient from five meters down, back up to the surface.
When we first tried to penetrate into the soil, it went down about 20 centimeters or so and then stopped. And we didn’t know why, so we started trying to figure out why, trying to figure out how we could help it get down. And we spent about a year and a half on various different methods and techniques trying to help the mole get down. We pulled the support structure off of it. We used our robotic arm to first press on it sideways to give it a little bit of friction. We eventually brought the scoop down on the end of the mole carefully and to keep it from bouncing out. But in the end, we were only able to get it to go down as far as, say, the back of the mole, flush with the surface of the soil. That was a really intense and difficult campaign.
We did things with the robotic arm that we had never planned to do that we’d never tested on Earth previously. We’d never expected to actually use the arm to do anything except to place the instruments on the ground. So we had a grapple that picked them up and then let go of them once we had them on the ground. But we ended up scooping the soil around. We ended up pushing on the mole as it hammered, doing all kinds of things that the arm was never designed to do and that we had not intended to do. But the team came up with lots and lots of clever and really creative ways to try to help things out. But in the end, Mars won in the sense that we weren’t able to get the mole to go out any further into the soil than we were.
So that was our biggest challenge. We really spent a long time doing something that was never planned and that we really hadn’t anticipated. And I think we learned a lot from that, both in terms of the reasons why the mole failed to penetrate. And also learned a lot about the properties of the Martian soil. So there was definitely a silver lining to that, but it was a big disappointment, and that was probably the saddest part of the mission.
Host: Aside from that disappointment, has this mission exceeded your expectations?
Banerdt: Yeah, it really has. And I think that’s saying a lot because I have a pretty active imagination. I had imagined a pretty fantastic mission. I think the only place where it really hasn’t exceeded what I had expected is the lifetime. I’d hoped that we would have wind coming along and blowing off the dust from the solar panels, and maybe we’d be taking measurements for 10 years, a dozen years or so. Looks like that’s not going to be. But meanwhile, already we have more than 1,300 quakes, and I was hoping to get maybe a few hundred quakes. Our weather station has turned out to be a really fantastic scientific asset, where we have probably the most detailed and continuous year of weather data anywhere that anyone’s ever done on Mars. I think that’s going to be really, really valuable for planners in the future, both for other landers and for human exploration.
Seeing these craters as they actually formed, I was skeptical that we would ever see a signal from a meteorite, although, I knew it was definitely possible. And we’ve seen over a half a dozen so far. So it’s really exceeded my expectations in almost every way. Like I said, it would’ve been nice if it would last longer. It’s already lasted twice as long as our planned prime mission, so I really shouldn’t complain. And of course, the mole was a disappointment, but I think the other science that we’ve gotten from InSight has more than made up for that.
Host: What happens when the mission comes to an end?
Banerdt: Well, first of all, we’re going to make sure that all of the data is processed and archived in publicly available places. We are putting all of our data into the Planetary Data System, the PDS, which is available to scientists, not only in the United States, but all over the world. And in addition, our seismic data is being placed on a site called IRIS, which is the international clearinghouse for seismic data all over the world. So, basically, every seismometer in the world, except for a few proprietary ones, they place their data on this IRIS site and it’s in a common format. So, anybody who does terrestrial seismology will be able to just put in the station code for our inside seismometer, download the data just like they would from a seismometer in Southern California or Alaska or Japan, and analyze it. So what we believe and what we think is clear is that this data is going to be a resource for decades to come.
And I know our team has been analyzing this data like crazy, but we feel like we’ve just scratched the surface of its potential. So we want to make sure that that data is all available, that all the information is there for people to use. And if someone comes back 10 years later, they don’t have to call me up and see if I can remember what some of the parameters were. We want to make sure that all the information is set up on that archive.
In terms of Mars seismology, this is probably the last seismic mission to Mars for quite a while. There’s a lot of interest in doing more seismology. One single seismometer can only do so much. We’ve been able to make these amazing discoveries because, seismologically speaking, it’s the low hanging fruit. But if we had multiple seismometers on Mars, we could start doing the kind of seismic analysis that people do on the Earth, and looking at a lot of the details of what’s going on in the mantle, what’s going on underneath some of the geological structures on Mars, and really understanding what causes those huge volcanoes, what causes the giant rifts like the Valles Marineris.
We’ve got lots of theories about that. Seismic information is really the best way to start actually getting at which of those theories is closest to reality. So a seismic network on Mars, multiple seismometers is really what we’d like to see eventually. And maybe a few decades from now, after Sample Return is behind us, or when they start really looking at sending humans to Mars, when that kind of effort’s underway, I think maybe we would be able to slip a few more seismometers in there.
But meanwhile, there’s lots of other targets in the solar system that are just begging for seismometers. There’s actually a seismometer scheduled to be flown on the Dragonfly mission to Titan. Dragonfly’s a helicopter, which is not the greatest place for a seismometer to be, but it does land and it stays on the ground for extended periods of time recharging its batteries. And during that time, the seismometer will be listening for Titanquakes and looking at the seismic noise, which can actually tell you quite a bit about a planet all by itself.
There’s a seismometer being readied right now to fly to the far side of the Moon for the first time. The Apollo missions back in the ’70s put four seismometers on the Moon and gotten a lot of really, really valuable seismic information about the deep structure of the Moon. But all the of the Apollo landers were pretty close to the sub-Earth point, really just centered on the Earth-facing side of the Moon. And so, this seismometer, which is called the Farside Seismic Suite, is going to be landed with a commercial lander on the far side of the Moon in a couple of years, and actually uses the flight spare of the inside seismometer, modified for lunar gravity. So, we’ll be getting some planetary seismic data pretty soon, but not from Mars.
We’re getting to the end of the mission. And probably, in the next month or two, we’ll lose contact with the lander. But I don’t really like to think of it as the lander dying on Mars. I like to think of it as going into retirement. It’s done everything that we’ve asked it to do. It’s never complained, had almost no technical problems with it. Very, very trouble-free spacecraft. And when we get to the point where there’s not enough solar energy to run the computer, our spacecraft actually goes into a mode we call dead bus mode. And what happens is it turns off all the electronics on the spacecraft, except for the circuits that charge the batteries. And so, if some time in the future a big gust of wind comes along, or a dust devil or something like that and would clean off the solar panels, it’ll actually charge the batteries up again and the spacecraft will wake up and start sending signals back to Earth.
And we have a campaign in place to actually watch for those signals. We can actually just listen to them on the side bands of other Mars communications. And so, it’s quite possible that sometime, a year from now, two years from now, maybe even longer, that InSight might decide that retirement’s too boring and come back out of retirement and decide to do some more work for us. And that’s pretty unlikely. I put the likelihood down in the less than 10 percent category, but that’s not like buying a lottery ticket. It’s a lot more likely than that. So I like to think of it as just resting on Mars and trying to decide whether it wants to go back to work again.
Host: That’s so fascinating. Bruce, thank you so much for joining us today on the podcast.
Banerdt: Oh, it’s really been my pleasure. I really love this mission. I’ve been living with it in some form for the last 10 years, and I’m really going to miss it when it’s gone.
Host: Bruce’s bio, links to topics discussed during our conversation, and a show transcript are available on our website at appel.nasa.gov/podcast.
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