Planetary Radio: Space Exploration, Astronomy and Science - How Long Was Mars Wet?

Episode Date: October 23, 2019

Planetary scientist Briony Horgan and her team want to know how long liquid water flowed on the surface of the Red Planet before that world froze. Long enough for life to appear and thrive? New work comparing Earth’s extremes may have provided clues. There’s gas in space, and some of it is inside astronauts. Bruce Betts shares the uncomfortable truth in this week’s What’s Up. Also, space headlines from The Downlink. Learn more about this week’s guest and topics at: http://www.planetary.org/multimedia/planetary-radio/show/2019/1023-2019-briony-horgan.htmlSee omnystudio.com/listener for privacy information.See omnystudio.com/listener for privacy information.

How wet was Mars, and for how long? This week on Planetary Radio. Welcome, I'm Matt Kaplan of the Planetary Society, with more of the human adventure across our solar system and beyond. Bryony Horgan has returned to share news about those long-gone days when the red planet looked much more like our own. How long did the water flow? Long enough for life to get a toehold? And when the freeze came, was it forever? Or were there multiple ice ages like those Earth has known? Also ahead is our weekly visit with the chief scientist. Dr. Betts and I recorded this week's What's Up early so that I could head out on a brief vacation.

That's why this week's show is a bit abbreviated. We'll begin with our new tradition. Here are three stories you can find in the October 18th edition of The Downlink, the weekly digest of planetary science and exploration edited by our own Jason Davis. We'll begin with the story that got most of the attention last week. While they would tell you it's no big deal in practical terms, the first spacewalk conducted entirely by women is still a milestone worth noting. NASA astronauts Christina Koch and Jessica Meyer successfully completed their work

outside the International Space Station right on time. This was the 421st time humans have gone EVA, beginning with that first stroll in the park by the late Alexei Leonov. The Hubble Space Telescope captured our sharpest look yet at comet 2I Borisov, only the second ever confirmed interstellar comet. It appears to be much like the comets we find inhabiting our own neighborhood. And here's great news. The mole temperature probe experiment on the InSight Mars lander

is hammering itself into the Martian soil, thanks to some help from the lander's robotic arm. Scientists on the project are thrilled. arm. Scientists on the project are thrilled. Go to planetary.org slash downlink for easy access to Jason Davis's latest news from around the solar system, published every Friday. I asked Purdue University Professor Briony Horgan to return when I read about a recent interesting investigation she led. Like so many other scientists who study Mars, Brioni wants to answer questions about that planet's distant past, a past that we now know included lots of liquid water on the surface. Understanding this may be vital to finding evidence of past life,

but answers are very hard to come by. Brioni, welcome back to Planetary Radio. I'm only sorry that, well, there you are in Pasadena, and I'm stuck at home way down to the south. I'm sorry that we couldn't meet face-to-face, but very glad to bring you back to the show. It's great to be here. Thanks for having me back. So it sounds like you're in a little bit of an echo chamber, and I've already heard doors opening once or twice. Where did you find, what quiet, a relatively quiet spot did you find there? Where are you, at Caltech? Yeah, I'm at Caltech just outside of the meeting room for the ongoing science team meeting for the Curiosity rover that's here right now.

So this is Curiosity. And, of course, last year when you were on the show, the landing site for the 2020 rover had just been selected. And we're going to get into that as well. But what I'm hoping we can begin with is this work that you reported on. You went to Barcelona, Spain for this, to a conference there to talk about the early Martian climate. That's correct. Obviously, this is something we care about a lot. We know that Mars had lots of water. We know it still has a fair amount. But is the popular dream or wishful thinking of ancient Martian seas and rivers, is that looking like it's close to the truth?

Or do we know enough to say yet? Well, that's the question we were trying to get at with this work. And so the question was, you know, what did ancient Mars look like? What was the climate? at with this work. And so the question was, you know, what did ancient Mars look like? What was the climate? You know, was it this warm, wet environment or was it covered in giant ice sheets, this very cold kind of ice locked world? And the reason we don't know is that, you know, we see all this evidence on the surface that there was liquid water. You know, the Curiosity rover has been roving through ancient lake sediments that we know were laid down in liquid water. But, you know,

is that representative of ancient Mars? Were there these long periods where water was flowing and rain was falling? Or was it mostly this very cold, dry, icy place with these very rare periods where you could have had surface water and then also, you know, lots of life possibilities for life on the surface? And so the reason we don't know is because of the faint young sun, which is this problem in solar system science, where early on the sun was actually a lot dimmer than it is today. And we know this from looking at, you know, other other young suns right now elsewhere in our galaxy. So when we take that into account and we say, OK, so how warm was ancient Mars three or four billion years ago?

What the models tell us is that, well, it was actually pretty cold because there was less sunlight coming in. So when you try to do a climate model and figure out what the climate looked like, what you end up with is a very cold, icy world. So this is kind of the problem we were looking at is how do you account for that along with all of the liquid water evidence we see? Is it that we don't understand what the climate was doing or that we don't understand what the geology is telling us? So that's kind of the underlying problem. What if the sun wasn't the only source of heat to keep that water liquid, at least for periods on Mars? That's also being considered?

Yeah. So one possibility is that, say, you had a giant impact or a huge volcanic eruption. That could add some heat to the atmosphere. And that could maybe help create short rainstorms or something like that but then you know can you create these what we think might be evidence for kind of longer periods of liquid water on the surface so that was the big question so with our group what we were trying to look at is you know do is there other geological evidence we can pull from to help us understand this and so we're looking at is the mineralogy and chemistry of the ancient surface because minerals are really sensitive to the environment they form in. They're really

sensitive to temperature, to how much water was present. And so what we were looking at is, okay, when we look at the places where minerals have formed due to interaction with rain and snow and things like that, do we see any evidence that they're recording a climate? So we found by looking at analogs on Earth, so places on Earth that have similar chemistries and kind of environments that we think persisted on Mars, we found that there are big differences in mineralogy when you go from a very cold, icy place like the tundra or the snowy top of a mountain to much warmer places where you have a lot of liquid water. When we compare that back to ancient Mars, what we see is more of the minerals that require liquid water, that require rain, that require these warm temperatures. When we look later on

Mars, say for example, around two or three billion years ago, we see more evidence for kind of the cold climates. So that's kind of what we were talking about in that talk. More about this technique of using what we know about our own planet to expand our knowledge of Mars. Is this partly because, you know, even with the success we have seen of the rovers on the surface over the last, well, it's a couple of decades now, we really just don't have enough data. We haven't been to the places that would give us more direct evidence on the red planet. Yeah, so that's one of the challenges, you know, that we've been to all these great landing sites with our rovers, but it turns out they're all relatively young. They all date from relatively recently in Mars' history.

Even the Curiosity rover, the lakes we're seeing there are sort of what we call sort of the middle, late period of Mars' history. called sort of the middle-late period of Mars' history. And so we don't really know if it's telling us about the earliest periods when we see all the evidence for flowing liquid water for rivers and big lakes and all of this. What's really exciting is that with the Mars 2020 rover, we think we might be going to one of those really ancient environments, to what we call the Nowakian era of Mars. It's the name of the geologic era that we assign to this most ancient period of Mars' history, 3.7 to 4 billion years ago. We think that there was a lake present in Jezero Crater during this time period. So once we get there with 2020, we'll be able to look at this, you know, on the ground, look at the rocks, try to understand how long the lake was there,

what was its chemistry, where did the water come from? Sounds like you are still pretty satisfied with the selection of Jezero crater as the target for the 2020 rover. I am. Yeah, I think the more we learn about it, the better it's getting. You know, as on the science team, we've been doing a lot of work to try to map the crater to get a better idea of where the rover's going to go. And the more we learn, the more cool stuff we find. So I'm really excited about it. But what about all those great orbiters overhead? Is a lot of this mineralogical data that you've talked about, is that coming from on high?

It is. Yeah. So that's how we know what most of the surface of Mars looks like is from these orbiters. And we have great mineral data at great resolution. The cameras we're using to do spectroscopy and interpret mineralogy can get down to 18 meters per pixel. So we can get down to kind of individual outcrops of rock and see what they're made of. When we look at that data, what we see are there are all these places on the most ancient terrains of Mars where we see what we call weathering profiles. They're basically deep sections of the crust. When I say deep, I mean on the order of, you know, tens of meters up to hundreds of meters deep that have been turned to clay. So clay is, you know, the mineral you find in the soil in your backyard, it forms when you have lots of water running

through rock. And in particular, when you see these, you know, big sections that have been basically leached to form this clay on earth, the way you interpret that is that there's been basically rain raining down on the surface for long periods of time to form a really deep soil, basically. And on Earth, when you see this in the geologic record, you can use this as a sign that there was this kind of stable period of a relatively warm and wet climate. And we see the same thing on Mars. And so that's where a lot of our data for this, it's one of the best pieces of evidence for a relatively warmer and wetter ancient Mars that we see on the planet today. I don't think we've yet in this conversation explicitly said why a lot of people who are hoping to find some past biological activity on Mars, why news that yes,

it was wet, liquid water, and for an extended period, why that would be really good news? Yeah, that's a great question. So when you think about, okay, where do you want to go look for life? You think about what are the most habitable environments that can support the biggest, the largest biodiversity, the most biomass, they're usually kind of warm and wet places, right? And they're also usually connected to a lot of other warm, you know, other kind of warm and wet places, right? And they're also usually connected to a lot of other warm, you know, other kind of warm, nicely habitable environments. So when we think about searching for life on ancient Mars, what we would love is to find one of those places that's just one location within a much broader habitable landscape on ancient Mars where life, you know,

life could have gotten in all of the crevices and really established itself and created a lot of biomass that we can then look for with our rovers as biosignatures. You know, if you think about the other option where Mars was kind of cold and had a lot of ice, that means that there weren't as many environments, especially at the surface, that were habitable over large areas and for long periods. You're probably going to get a lot less biomass, but many fewer biosignatures preserved. If that's the case, and you probably have to go look in a very different location to look fewer biosignatures preserved. If that's the case, then you probably have to go look in a very different location to look for biosignatures. One of the great ideas people have had is, well, why don't we go look in the subsurface? The subsurface is probably always

habitable. The problem is that's a lot harder to do. You don't get as much biomass down there anyway. And so really the ideal situation is a nice, warm, habitable lake with lots of organics hanging around that's producing lots and lots of biomass that we can look for with our rover. And so that's kind of what we're hoping for. And so far, our results are suggesting that there was at least one period of Martian history where that was true. How long it was, we don't really know. If that happened more than once, we don't really know. But it's at least telling us that it's possible. So you've just gotten to what I wanted to ask you about. We just can't say yet how long water might have been flowing on the surface.

And did it only happen once? I mean, were there ice ages on Mars just like there were on Earth where the ice came and went? Yeah, so there almost certainly were ice ages. We see evidence for that on more recent Mars, very clearly. You see evidence that ice has moved around all over the planet. And really, the recent modern terrains on Mars have experienced that are really chewed up by that process. When we look at ancient Mars, we don't see as much physical evidence for ice. And that's one of the reasons that we think kind of supports this idea that there was at least one relatively warm period.

It may have been much longer and not too many periods where ice was dominating the surface. But that doesn't mean it wasn't there. Right. We certainly it could have been ice came and went. It could have been warm and wet in this case really just means mostly fairly warm, but still pretty snowy or icy a lot of the year. You know, there's lots of sort of permutations on that that could have been true. or icy a lot of the year. You know, there's lots of sort of permutations on that that could have been true. So if you were writing the next decadal survey all on your own for what we should be doing at Mars, regardless of how much it might cost to build the robot to do this work or to send humans there for that matter, what would you most want to see?

Would you want to get under the surface or what? Well, I think both, right? I think, you know, with Mars 2020, we're going to do a great job investigating this ancient, really ancient lake environment, helping us understand what the surface looked like. It's going to be a little, you know, it'll be a little more challenging to tie that directly to climate. And so one place it would be great to go are some of these, you know, ancient, deep weathering profiles that I just talked about. And actually the ExoMars rover from

ESA is planning on going to sort of the periphery of some of these large areas that have been weathered like this. Not quite in the middle of it, but it's going to try to get at some of that. So we're pretty excited about those results. But then I do think one thing you definitely want to do going forward is to try to understand what are the other habitable environments that existed. And I think the subsurface is a really important one that we do need to investigate. You know, we're hoping that with Mars 2020, if we can get out of Jezero crater and get onto the surrounding terrains, when we look at those areas, it's this really weird mishmash of things, you know, huge blocks and mega breccia and all these weird

geological things that we think might be related to ancient impacts laying down all this material. We see evidence that water moved through there and left behind these big veins and things. And so we think there is some evidence for a deep environment, a deep subsurface environment that existed in those terrains outside of Jezero crater. But there are other places we can go to, right, that we can try to understand these better better so i think those are definitely some of the things i'd want to look at i actually study modern mars quite a bit too and one of the big things we'd love to understand is more about the modern climate on mars and one of the best places to go do that is to go to the current uh ice cap so the north pole in particular because it has these beautiful records of just ice and dust and sand deposition

that extend all through the ice cap. And one idea is that if you could drill into the ice cap, extract an ice core, or at least look at how it's changing with depth, you could actually reconstruct the recent climate of Mars, which would then help us understand how climates work on other planets. It would help us validate our climate models for ancient Mars. It would just be really, really helpful. So I think that's another idea I would really love to see happen going forward. Just like ice cores taken from the Arctic and Antarctica down here on Earth have revealed the relatively recent past. That's pretty exciting. Yeah. It sounds like not only do we hope for great new science from the 2020 rover,

but from what you've just described, that we can also look forward to some spectacular new panoramas and up-close images. Yeah, so that's one of the things we're really excited about. Jezero Crater is going to be a spectacular place to explore. We're going to come up against this huge delta, which has this beautiful cliff face along the front of it. We'll be inside of the crater itself. We'll be able to see the crater rim.

We're eventually going to climb up the crater rim, be able to look back down to the crater and onto the terrains beyond. It's going to be a really spectacular landing site. Can't wait. And of course, we're looking forward at the Planetary Society to those seven minutes of terror because we'll wrap another event around that. I think we're going to have another big party, hopefully one of our Planet Fest that took place for the arrival of the Mars Exploration Rovers and, of course, more recently, Curiosity. And since you're in town to talk about Curiosity, anything else you want to say about the science that's being returned by that very successful mission? Yeah, well, Curiosity, you know, we've been on the ground now for over how many years now? Over seven years. And we're still doing just incredible, incredible science. Just earlier this year, we finally got to another really big target that we had seen from orbit we wanted to get to, which is this big layer, just chock full of clay minerals in Gale Crater. And so we're just investigating that now. And we're getting some of the first results back of really trying to understand why those clay minerals are there. What's their mineralogy? You know, how, what do they have to do with this ancient lake environment? And so we're just now

starting to process that and work it out. But it's been, it's very cool to see all this amazing science still coming back from this rover. Absolutely. Great stuff. Before we finish, if you don't mind me turning personal for a moment, when and why did you become a Martian? Oh, that's a great question. So I actually didn't start out as a geologist. I started out as a physicist and I have a degree in physics, but I always loved exploration and space. And, you know, actually, the thing that turned me on to planetary science was Carl Sagan. I was trying to figure out what I wanted to do.

And someone just happened to give me a copy of the book version of Cosmos. And I read that, and it was just completely blown away that planetary science was a real job. It was a real career you could have. And so that was basically no turning back at that point. So I went off to grad school in a totally different field and learned geology, and now I look at rocks on Mars with the rover, and it's great. Briony, thank you again. great. Briony, thank you again, as has been a great update, not only on the science that is currently underway, but looking forward to what we hope we will learn from Jezero Crater and its surrounding region there on the red planet. I sure hope that we can check back with you,

keep checking back as we head into that new mission scheduled to arrive in February of 2021. I'm looking forward to it too. Planetary scientist Briony Horgan is an assistant professor in Earth Atmospheric and Planetary Sciences at Purdue University. She is a co-investigator on both Curiosity and the Mars 2020 mission that will soon be landing that even more sophisticated rover on the red planet. What's up with Bruce Betts? Arrives right after a break. This is Planetary Radio.

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There are thousands of confirmed worlds orbiting other stars. Here's your chance to explore them and understand how they were found. And you can do it for free. Thank you. dot com slash planetary. That's thegreatcoursesplus.com slash planetary for a full month of free lectures and courses. I'll see you in class. Time for what's up on this vacation edition of Planetary Radio. Well, my vacation anyway. We're going to hear about the night sky, my vacation night sky, I hope, from Bruce because we're recording this several days ahead of time. Welcome back. Thank you, Matt. Where are we going? Shotgun. Well, when you're on your vacation, you can check out planets in the night sky. We've got Jupiter hanging out in the evening still over in the West. Saturn is to its upper left. Jupiter is super bright.

And you can see the moon hanging out with Jupiter on the 30th and 31st. So if you're Halloweening, you can check out the crescent moon between Jupiter and Saturn in the southwest in the evening. The crescent moon, a little bit bigger moon, hanging out. Well, you know, the phase is bigger. Hanging out near Saturn on November 2nd. In the pre-dawn sky, Mars making its way up. Still pretty low, but over in the east in the pre-dawn. The moon will be with it on the 26th of October.

Again, tough to see, but pretty cool if you can see it. And Uranus at opposition on October 27th, so best time to see it, but you're going to need a finder chart, binoculars, or a telescope to do so. That's pretty much our night sky wrap-up. Challenging, but busy. On to this week in space history. In 2001, Mars Odyssey arrived at Mars, began operations, 18 years, still working. Amazing.

These stories are inspiring because, of course, there were humans who put these wonderful machines together. Well, it was actually aliens. Oh, never mind. That explains it. Don't include that part. Martians must be maintaining it. Okay, that explains a lot. Not really.

Alright. On to random space fact. So Matt, have you thought about burping in space? Excuse me, endlessly. Because I hadn't really thought it through, and according to some of the food experts from NASA,

you don't want a lot of things like carbonation or things that'll make you burp because you're much more likely to have a wet burp rather than a dry burp because the food is just floating around in your stomach, hanging out near the sphincter that leads upwards in a earth environment, but just leads towards your head in a space environment. And I said this very clumsily, but yeah, wet burps to be avoided. I've heard exactly this from at least one and maybe more than one astronaut, that it's one of the downsides, well worth the trouble of traveling up there, though. You're well-versed in wet burping.

traveling up there, though. You're well-versed in wet burping. I wish I could say I personally had experienced this. For that reason, sadly, I've only experienced the terrestrial variety. All right, then we will move on. There's not been more of the views from you, so we will go to the trivia

contest. And I asked you, what is the diameter of the rover Curiosity's wheels? How'd we do, Matt? A pretty great response to this. Laurel Bischow had to wait over two years to come up a winner again, but it's happened. Random.org has chosen this regular listener in Pennsylvania. Laurel says each wheel's diameter is about 20 inches, 50 centimeters,

correct? That is correct. Congratulations, Laurel. I hope it was worth the wait. I'm sure it was. We're going to send you a KICK Asteroid, Rubber Asteroid, Planetary Society Rubber Asteroid, and one of those 200-point itelescope.net astronomy accounts. You can look at some of the stuff Bruce just talked about. We, of course, have others to read. Bjorn Fredberg in Sweden, we haven't had any humorous measurement units in a while. He said, sure enough, 20 inches, 50.8 centimeters, or approximately 16.46 adoparsecs. I didn't know this. There is a list of humorous units of measurement in Wikipedia, and he even provided a link to it. Maybe we'll put that on the show page at planetary.org slash radio. Several listeners found the correct answer in this book that is

apparently called The Design and Engineering of Curiosity, page 166. I've heard of that. It's this Lactawala, comma, E. We'll have to check it out. Robert Johannesson in Norway, we're hearing from Scandinavia a lot, says,

yeah, about the same diameter as a large New York-style pizza. Let's all hope there will one day be just as delicious pizza on Mars and beyond. Yum. John Polucci in Tennessee, I think it's the first time we've heard from him, he remembered that as Curiosity rolls across Mars with those 50-centimeter wheels, it's leaving Morse code that says JPL, JPL, JPL all over and over and over.

He has calculated that it has written this in the Martian sand over 249,000 times. What? Wow. A limerick this time rather than a straight on poem. And it comes from David Douthit in West Virginia. If driving on Mars is your deal for endurance and some sex appeal, not a white wall or a spinner, machine treads are a winner for each 20-inch aluminum wheel. Ah, poetry. We have heard from everybody we need to. We're ready to go on to

a new contest with a really cool one-time prize. All right. Keep in the theme. Who was the first person to eat, and possibly burp, but that's not a requirement. Who was the first person to eat in space? Go to planetary.org slash radio contest and get us your entry. I think I know. Anyway, the deadline is October 30th. That'd be Wednesday, October 30th

at 8 a.m. Pacific time. And you'll win yourself, in addition to that 200-point iTelescope account for astronomy, how about a copy of a new game? Very appropriate. It's called The Search for Planet X. It's from a little company called Foxtrot Games that has a Kickstarter underway as we speak, but not for much longer. They've been doing very well and they have some stretch goals underway now. I hear that you've seen this game, you've examined it? I have released a prototype and it's interesting. It folds in the scientific method behind trying to find a planet, usually called Planet Nine, at least by Mike Brown and colleagues, that they find evidence it's out there, but we haven't found it yet. So this actually makes game out of it, and it seems pretty fun. So there's a board game, but it comes with a companion app that you use throughout the game

to survey the sky. You go to conferences and you can get your submissions peer reviewed. Of course, if you're already a scientist, maybe you're not looking forward to that, but if you're not, it might be fun. Nothing says unlike conference presentations and peer review, but they are critical parts of the scientific process that a lot of people aren't really aware of, and so having that in a game form is pretty cool. Anyway, it's called The Search for

Planet X, and somebody is going to win it if you got the right answer and you're chosen by Ranma.org in this new contest. We are done. All right, everybody, go out there, look up in the night sky, and think about what else? Space burps!

Thank you, and good night. Here's what my grandfather used to say. It's better to burp and bear the pain than not to burp and bear the shame. Except he didn't use the word burp. Bye, Bruce. Bye, Matt. He's the chief scientist for the Planetary Society who joins us every week here for What's Up.

Want to learn more about that board game, the search for Planet X? You can go to foxtrotgames.com slash planetary. Planetary Radio is produced by the Planetary Society in Pasadena, California, and is made possible by its members who want to meet some Martians, even if they're long dead and microscopic. How about you? Join the club by visiting planetary.org membership.

Mark Hilverde is our associate producer. Josh Doyle composed our theme, which was arranged and performed by Peter Schlosser. I'm Matt Kaplan, at Astra.