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Planetary RadioOctober 23, 2019

How Long Was Mars Wet?

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On This Episode
Briony Horgan
Briony Horgan

Assistant Professor, Earth, Atmospheric and Planetary Sciences, Purdue University

Headshot of Bruce Betts
Bruce Betts

Chief Scientist / LightSail Program Manager, The Planetary Society

Headshot of Mat Kaplan
Mat Kaplan

Planetary Radio Host and Producer, The Planetary Society

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.

Briony Horgan with Curiosity

Purdue University photo/John Underwood

Briony Horgan with Curiosity
Briony Horgan, a professor of earth, atmospheric and planetary sciences, searches Mars for clues about its early history, and ours.
Ancient Mars with water

NASA / Goddard Space Flight Center

Ancient Mars with water
Isotopic measurements by researchers at NASA's Goddard Space Flight Center indicate that an ocean once covered approximately twenty percent of the Martian surface.

Trivia Contest

This week's prizes:

The new board game and app called The Search for Planet X, and a 200-point astronomy account.

This week's question:

Who was the first person to eat in space?

To submit your answer:

Complete the contest entry form at or write to us at no later than Wednesday, October 30th at 8am Pacific Time. Be sure to include your name and mailing address.

Last week's question:

What was the first star system besides our own that was discovered to have eight planets?


The winner will be revealed next week.

Question from the October 9 space trivia contest:

What is the diameter of the Curiosity rover’s wheels?


The wheels on Curiosity have a diameter of 50 centimeters or about 20 inches.


NOTE: This automated transcript is currently being edited by a human. Check back soon for updates.

[00:00:00] How wet was Mars and for how long this week on planetary radio?

Welcome. I'm at Kaplan of the planetary Society with more of the Human Adventure across our solar system and beyond briony 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 [00:01:00] 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 Cook and Jessica Meier successfully completed their work outside the International Space Station right on time.

This was the 420 first 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 to I borissov only the second ever confirmed Interstellar Comet. It appears to be much like the Comets we find inhabit in our own.

And here's great news the mold temperature probe experiment on the Insight Mars Lander is hammering itself into the Martian soil. Thanks to some help from the Landers robotic [00:02:00] arm scientist on the project are thrilled. Go to planetary dot org slash downlink for easy access to Jason Davis is latest news from around the solar system published every Friday.

I asked Purdue University Professor. Brownie Horgan to return When I read about a recent interesting investigation. She led. Like so many other scientists who study Mars Brian he wants to answer questions about that planets 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.

Bryony, welcome back to planetary radio. I'm only sorry that well, there you are in Pasadena and I'm stuck at home weight 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 great to be here. Thanks for having me back. So it sounds like you're a little bit of an echo chamber and [00:03:00] 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 a 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 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 or wishful thinking of ancient Martian?

Season Rivers is that looking like it's close to the truth, or do we know enough to say happy? Well, that's the question. We were trying to get [00:04:00] 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 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.

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 is actually a lot dimmer than it is today and we know this from looking at you know other other young Sons right now elsewhere in our galaxy. So when we take that into account when we say, okay, so how warm was Ancient Mars?

Three or [00:05:00] four billion years ago what the models tell us is that well was actually pretty cold because there was less sunlight coming in when you try to do a climate model and figure out what the climate looked like will you end up with this is 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, you know, is it is that we don't understand what the climate was doing or that we don't understand what the geology is telling us.

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 four 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 is 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 [00:06:00] 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 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 analogues on Earth so places on Earth that have similar chemistry and kind of environment 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 too much warmer places where you have a lot of liquid water and we compare that back to Ancient Mars that we see is more of the minerals that require liquid water that require rain that require these warm temperatures.

We look later on Mars, they for example, you know around two or three billion years ago. We see more evidence for kind of the cold [00:07:00] climates. So that's kind of what we were talking about in that sock. 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 all a couple of decades. Now. We really just don't have enough data. We haven't been to the places where 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 were seeing there. Our sort of what we call 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 [00:08:00] noachian era of Mars. It's the name of the geologic era that we. Assigned to this most ancient period of Mars history three point seven two four billion years ago.

We think that there was a lake present in Jezreel crater during this time period so once we get there with 2020 will 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 Jezreel crater as the as the target for the 2020.

I am yeah, I think the more we learn about it the better it's getting you know, as on a 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 to 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. It's from these orbiters and we have great mineral data, [00:09:00] you know at Great resolution. The cameras were 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 and we look at that data what we see are there these all these places on the most ancient terrains of Mars where we see what we call weathering profile if they're basically.

Deep sections of the Crusty when I say d by mean on the order of tens of meters up to hundreds of meters deep that have been turned to Clay. So Clay is the 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 I 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 and use it 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. [00:10:00] This is 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 hit liquid water and for an extended period why that would be really good news. Yeah. It'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 are 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 nicely habitable environments.

So we think about searching for life on Ancient Mars 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 [00:11:00] gotten in all of the crevices and really established itself. Great 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 many fewer biosignatures preserved if that's the case and you probably have to go look in a very different location to look for biosignatures.

One of the great ideas people have had as well. Why don't we go look in the sub surface and subsurface was 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 [00:12:00] know if that happened more than once. We don't really know but 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 that how long water might have been flowing on the surface and and did it only happened. Once I mean were there ice ages on Mars just like there were on Earth were the ice came and. Yeah, so they're almost certainly were ice ages. We see evidence for that on you. No more recent Mars a very clearly you see evidence that ice has moved around all over the planet and really the recent modern trains on Mars have experienced that are really chewed up by that process.

We look at Ancient Mars. We don't see as much physical evidence for for ice. And that's one of the reasons that we think kind of supports this idea that there was a lie. 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 that warm and wet and this case really just means. Mostly fairly warm but still pretty [00:13:00] snowy 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 decade will 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 me.

What would you most want to see? Would you want to get under the surface or. Well, I think both right I think you know with with Mars 2020 we're going to do a great job investigating this ancient really ancient Lake environment. Helping us understand what the surface looks like. It's going to be a little you know, it'll be a little more challenging a tie that directly to climate and so one place it would be great to go or some of these, you know ancient deep weathering profiles that I just talked about and actually the exomars Rover from Isa 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 it 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.

What are the [00:14:00] other habitable environment 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 j0 crater and get onto the surrounding terrains when we look at those areas. It's this really weird mishmash of things huge blocks and mega Beretta 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 Jezreel crater, but there are other places we can go to right that we can try to understand these better.

So I think those are definitely some of the things I'd want to look at is actually studying modern Mars quite a bit, too. One of the big things we 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 ice cap. So the North Pole in particular because it has these [00:15:00] beautiful records of just ice and dust and sand deposition that extends 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 the depth you can actually reconstruct the recent climate of Mars, which would then help us understand how climates work on other planets it would help.

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 be down here on Earth have revealed the relatively recent past that is 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 and up-close images. Yeah, so that's one of the things we're really excited about jazz Rock Raiders going to be a spectacular place to explore.

We're going to come up against this huge Delta which has this beautiful Cliff [00:16:00] face along the front of it. We'll be inside of the crater itself will be able to see the Crater Rim are eventually going to climb up the crater room be able to look back down to the crater on to the terrains Beyond going to be a really spectacular Landing site.

Can't wait and of course, we're looking forward if 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.

Yeah, well curiosity, you know, we've been on the ground now for over how many years now over 7 years and I'm still doing just incredible incredible. 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 of just chock-full of clay minerals in [00:17:00] Gale crater.

And so we're just investigating that now we're getting some of the first results back. I've really trying to understand why those clay minerals are there was there mineralogy, you know, how do they have to do with this ancient Lake environment? 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 size 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 martial?

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 when 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. You know went off to grad school and the totally different field and learn geology. And now I'd look at rocks on Mars but the Rover and it's [00:18:00] great brownie. Thank you again as just been a great update not only on the science that is currently underway.

But looking forward to what we hope we will learn from Jezreel crater and its surrounding region. They're 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.

Brownie. 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. Here's another word or two about the Great Courses plus and it's thousands of lectures on pretty much any topic you can think of and some you might not think of all [00:19:00] presented by the best professors from throughout the United States. You may have heard me mention that I'm a big fan.

My wife and I have a Shelf full of their courses. You'll find lots that cover the same things. We talked about on planetary radio including. The search for exoplanets what astronomers know there are thousands of confirmed worlds orbiting other stars. Here's your chance to explore them and understand how they were found and you could do it for free.

In fact planetary radio listeners can get a full month of no cost access to the entire Great Courses plus Library sign up and start learning with our special URL the Great Courses Planetary, that's the Great Courses 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 wall my vacation. Anyway, we're going to hear a about the [00:20:00] night sky my vacation night sky, I hope from Bruce because we're recording this several days ahead of time. Welcome back. Thank you mad where 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 super bright and you can see the moon hanging out with Jupiter on the 30th and 31st.

So if your. Halloween inning, you can check out the Crescent Moon between Jupiter and Saturn in the southwest in the evening the moon Crescent Moon 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. [00:21:00] Begin tough to see but pretty cool if you can see it and Uranus at opposition on October 27, so best time to see it, but you're going to need finderchart binoculars or a telescope to do so, that's pretty much our nice guy wrap up challenging but busy on 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, I was actually aliens but oh never mind that explains it Martian that part martians must be maintaining it. Okay that explains a lot. Not really. All right onto random space fact. So Matt, have you thought about burping and space?

Excuse me endlessly as I hadn't really thought [00:22:00] it through and according to some of the food experts from NASA. You don't want a lot of things. Carbonation and things that will 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. I said this very clumsily. But yeah what 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 are well-versed in. What burping?

I wish I could say. I personally had experienced this at for that reason sadly. I've only experienced the terrestrial variety. All right, then we will move on our the fuse from you. So we will go to the trivia contest [00:23:00] and I asked you what is the diameter? Of the rover Curiosity has wheels. How do we do math a pretty great response to this Laurel be show had to wait over two years to come up a winner again, but it's happened. has chosen this regular listener in Pennsylvania. Floral says each Wheels 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, I telescope dotnet astronomy accounts.

You can look at some of the stuff Brewster's talked about we of course have others to read. You're in fredburg in Sweden. We haven't had any humorous measurement units in a while. He said sure enough 20 inches 50 point eight centimeters or approximately [00:24:00] 16 .46 a toe parsecs. 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 of planetary dot org slash radio several listeners found the correct answer in this book that is apparently called the design and Engineering of curiosity page 166. It's by heard of the it says it's locked away Allah, any leftover want to check it out?

Yeah, Robert Johannes. 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 pallucci in Tennessee. I think it's the first time we've heard from him.

He remembered that as curiosity. Rolls across Mars [00:25:00] with those 50 centimeter Wheels. It's leaving Morris code that says JPL JPL JPL at all over and over and over. He is calculated that it has written this in the Martian sand over two hundred and forty nine thousand times. Wow. Wow. 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 in some sex appeal not a white wall or spinner machine Treads are a winner for each 20 inch aluminum wheels. Poetry we have heard from everybody. We need to we're ready to go onto 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 is the first person to eat in space go to planetary dot org slash radio contest and get [00:26:00] us you're. I think I know anyway, the deadline is October 30th. That would be Wednesday, October 30th at 8 a.m. Pacific time and you'll win yourself in addition to that 200-point. I telescope 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 fault 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 the 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 [00:27:00] 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 course, if you're already a scientist, maybe you're not looking forward to that. But 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 and that a lot of people are. Really aware of and so having that in a in a game form is pretty cool. Anyway, it's called the search for planted X and somebody is going to win it. If you got the right answer and your chosen by random dot organ this new contest we are done.

All right, everybody go out there look up in the night sky and think about what else space verbs. Thank you and good night. Here's some my grandfather used to say it's better to burp and bear the pain the not to burp and bear the shame except he didn't use the word burp by Bruce. [00:28:00] I'm a 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 Foxtrot 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. How about you join the club by visiting planetary dot org slash membership Mike Hill Verdes our associate producer Josh Doyle composed our theme which was arranged and performed by Peter Schlosser.

I'm Mat Kaplan Ad Astra.

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