2017 LPL Evening Lectures
An Underground Look at Mars Climate and Evolution by Lynn Carter - October 4, 2017
05 Oct 2017
Chapter 1: What is the background of the speaker and their role in Mars research?
I had a chance to meet her a number of years ago when I was at the Goddard Space Flight Center, and that's where she has spent quite a bit of her time. But initially, her undergraduate degree was in sciences at the University of Illinois, and then she did a master's and a PhD at Cornell University in astronomy.
Um, after that, she did, uh, post-doc at the Smithsonian Institution in Washington, D.C., and then, uh, began working as a research scientist at the Goddard Space Flight Center. And that's, uh, for those of you that, uh, know it as a fantastic place. For those of you that don't, it's-it's really is an extraordinary, uh, place, uh, for space sciences research.
It has almost 10,000 people that work there. It, uh, basically is, uh, involved in just about every space mission that, uh, takes place in-in the United States.
Over the time that she was there working with NASA, she received a number of different awards, including a fellowship for early career researchers and planetary sciences, group achievement awards for SHRAD, which is a ground-penetrating radar for Mars, which you'll hear more about this evening, as well as an early career, uh, achievement medal.
Um, she's worked on a number of different spacecraft missions, uh, SHRAD, which I- I mentioned, but also, uh, the MiniRF, uh, science instrument, which is, uh, a radar, uh, instrument, uh, uh, for the, uh, the moon. Um, and has worked on a number of other, uh, Mars-related, uh, missions, uh, including the RIMFAX radar, which is a ground-penetrating radar for the upcoming Mars 2020 rover.
Um, the Reason radar, which is for a very exciting flagship mission to, uh, the Jupiter system, and particularly to Europa. Um, she also serves now as the Deputy PI for the Mini-RF, uh, instrument. This is, um, that, uh, uh, radar for, for the Moon that I mentioned before on the Lunar Reconnaissance Orbiter.
and is a co-investigator on a joint venture with an international partnership with CREA, an instrument called ShadowCam. So in addition to all these fantastic mission opportunities, she is a fantastic scientist that has worked on not only the Earth and Mars and Europa, as I mentioned, but the Moon and also the very veiled planet of Venus, which is where a lot of her PhD work came from.
So, at this point, I'd like to be able to introduce our speaker, and again, if you have questions at the end, please don't hesitate to put up your hand. We'd like to be able to hear your questions as well. Thank you.
Okay. Hello, everyone, and thank you, Chris, for that very good introduction. I'm really happy to be here tonight to talk to you about radars and Mars climate and how we're using radars to look at the stratigraphy of Mars to understand the climate better. U of A is really famous for the HiRISE instrument on Mars Reconnaissance Orbiter.
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Chapter 2: How has Mars climate changed over time and what evidence do we have?
down here so I mean this is like the tilt is swinging back and forth pretty dramatically over pretty short time scales so this means that Mars has some crazy seasons going on so we would expect to see that in the rock record and so this is one of the things that we'll look for and also one of the things that could have caused Mars to be habitable sometimes and not habitable other times is this swinging around of the tilt of the orbit really changes the seasons on Mars a lot and it makes some places
more habitable or a better climate to have life than at other times it's just colder. Okay, so one of the first things we did with Sharad was look at the polar caps. One of the advantages of ice to the radar is that it's really transparent. Ice can go a really long way, or radar can go a really long way through ice. So these ice caps at the poles of Mars seem like a great target for the radar.
And these ice caps, so they look really different. So this is the north polar ice cap. This is the south polar ice cap. This north polar ice cap, when people try and age date it using cratering and relative stratigraphy techniques, it looks like it's only a few million years old, so it's very young. which is kind of interesting.
And then the south polar cap, when people try and date it, it's pretty old, like tens of millions of years. But remember that the obliquity swings back and forth a lot just on that less than a million year time scale. So these polar caps could record that obliquity swinging back and forth in them.
And I don't know if some of you have seen this, but we actually use Antarctic sounding to understand Earth's climate. So we go and we take core samples of Antarctica and you can look and see volcanic eruptions layered in that ash. You can look at the isotope ratios that are there and find how the climate's changed through time.
And so we kind of thought this was like an analogy that we could do on Mars, looking at the polar caps and trying to get climate information out. So this is the north polar cap, and it's really kind of striking that you see all these really fine layers in the polar cap. So the charade team has been able to go and actually tie these layerings into the obliquity cycle of Mars.
So if you go and look at some of these layers and sort of form them into packets, like you can see there's this top layer here and then there's a gap and then there's other packet layers. Some of these can be correlated to that climate record where when you watch the obliquity swings and you go back at the age that you expect this polar cap to be,
it looks like that layering is caused by the seasonal changes on Mars, basically. And so this preserves a record of those obliquity changes. We think what happens here might be that when it's warmer, for example, you preferentially remove some of this ice and you get a lag deposit that's just the dust that was in there. Mars is very dusty, so there's always dust being deposited on here.
But if you had dust in the ice and then you just sublimate or evaporate some of that ice off, then what you're left with is just this dusty layer. And so you might have these dusty layers caused by these seasonal changes basically all the way through the cap. And so we think that's what we're seeing in this case.
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Chapter 3: What are the different radar technologies used to study Mars?
And so these instruments were really selected to develop that context. And so the RIMFAX radar, is on the back and so we were selected to look at the subsurface in this profiling mode.
RIMFAX will have higher resolution than Chirad and Marsis and it'll be more like the systems that people use for archaeology on the earth that you pull by hand and except this one will be remotely operated on a rover.
And so then whenever the rover's driving, we're pinging the surface like this, and then it's the same thing where whenever the radar wave hits an interface in the stratigraphy, we'll see an echo back from it. So then we'll be able to, you know, as the rover's going along, see what's underneath the surface.
And a major reason why people wanted to have a radar on this was because they realized with the other rovers that they had this problem
where they would see a unit and it looked really exciting and so they would be sampling it or looking at it or whatever then they would drive off and they often had no idea how that unit connected to what they went to next because Mars is very dusty, units can be dipping, maybe you don't see where that unit went and so what they're hoping is that with this system we will be able to track those units so that if you sample one unit or look at one unit
then you drive off, you can see that, oh, it went under this, or like, oh, it's part of this other piece of the stratigraphy, which is context that we didn't have before ever. RIMFAX, I think, now will be the first GPR on Mars. So the Europeans are going to send an instrument as well,
but now it looks like they've been delayed so long that we might actually arrive first, not that it's a competition. But, and actually like our principal investigator, he's Norwegian, Sven-Erik Cameron, and this radar is being provided by the Norwegian Defense Research Agency.
But he was actually on the other one too, and now he's happy he won this one in the competition because it's probably going to get there first. But he's associated with both of them, so it's lucky for him. So this is the frequency that we're operating at, 115 megahertz to 1.2 gigahertz. Basically, the wavelength's a lot shorter. So we have higher resolution, but we don't see down quite as far.
This radar would not see to the base of the polar cap. but we don't have to, we're only interested in what the rover is driving over. So we'll penetrate maybe 10 to 100 meters, and we kind of expect most places will penetrate maybe 20 meters or something, not that far. And we have five to 10 centimeter vertical resolution, so we'll be able to see things at pretty fine layers.
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Chapter 4: How does radar technology improve our understanding of Mars' geology?
And the thing about these two that people like is that there's carbonates there. So these are some of the only places on Mars where we know that there's carbonates. And there's also very old rocks. So if we go to one of these sites, we'll have access to the oldest rocks that we've ever seen from a Mars mission. So that would be pretty exciting.
So I just wanted to show you a little bit about where these are. So this is Jezero Crater. So one of the landing sites is in here. Never mind all this. I just wanted to show the context. And Northeast Sirtis is up here. So they're very close to each other. So in a way, we'll be sampling the same types of rocks. But the landing sites are sort of different.
So Northeast Sirtis is this beautiful, almost Monument Valley mesas, except not that big, really. Here's a diagram of one of the mesas. So this is 5 meters by 100 meters.
and so the ability to even land amid all this terrain is being made possible by the fact that JPL has developed a new landing system which will be more precise so it's sort of this incredible terrain and what we would want to do here is sample these olivine carbonates so on earth carbonates are often associated with life here we think these carbonates may have been formed and associated with the volcanics
So they might not be biological. In fact, the going assumption is that they're not. But it's definitely interesting. And it's something that's new and that we don't really have any evidence for. All of these rocks are really old. So they're from the time period when the valley networks were forming.
So it's a time in Mars history that we've never sent anything that's someplace that's this old before. One of the things about the Northeast Sirtis site is that people think it's a good place to look because you've shaved off these mesas to look at hydrothermal systems because it looks like those carbonates may have been formed through water interaction in rock.
So it might have been a situation like this at one time. And this is a picture that National Geographic made for this site in particular, that this is the picture that people sort of have for what it could have been like. So it looks totally different than this now, but that was billions of years ago.
Another thing that I think is really interesting that I hadn't thought about before I started working on this is this mega breccia, the possibilities of these mega breccias. So when you have impacts, they throw out huge blocks of material. And these are some of the blocks. So this is a 100-meter scale bar. And these are giant rocks that have been thrown out by an impact.
And you can see tons of layering in these rocks, too. And we think these were thrown out by very large impact craters that could have excavated things from really below the surface. And so these rocks, probably things that were from originally below the surface and they've been chucked out onto the surface.
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