New Impact Craters on Mars

MRO Media Telecon- Sept. 24, 2009

Jane Platt: Thank you very much, and good afternoon, everybody. Thanks for joining us for this media telecon. I'm Jane Platt with the JPL Media Relations Office. Our topic today is some intriguing findings from NASA's Mars Reconnaissance Orbiter.

They're published in this week's Journal Science. We have three panelists today who will speak, and then we'll be taking questions from reporters. And as the operator mentioned, if you think of a question, press star one at any point and you'll be put in the queue. A reminder that visuals for this briefing are online.

If you're not there already, I'm going to give you a long URL and then a short way to get there. I'll give you the short way first: www.nasa.gov/mro. And you can click there where it says visuals and materials for the news telecon. And the long URL is www.nasa.gov/mission_pages/MRO/news/mro200909224.html.

Okay, so first I'm going to introduce our three scientists with Mars Reconnaissance Orbiter. We are going to hear first from Ken Edgett of Malin Space Science Systems in San Diego. He's on the Context Camera team. And then Shane Byrne, the University of Arizona, Tucson, with the High Resolution Imaging Science Experiment, or HiRISE, as it's called. And Selby Cull from Washington University in St. Louis with the Compact Renaissance Imaging Spectrometer for Mars. Let's start off with Ken Edgett.

Ken Edgett: Good afternoon. Late last year, 2008, Shane and Selby and I and our 15 coauthors on the paper being published today in Science, we discovered five places on Mars that have relatively clean subsurface water ice that was exposed by newly formed meteor impact craters. And these were located in places where we were not expecting to see ice, just a few feet below the ground. We think all five of these new impacts occurred during the first half of 2008, and we watched as the ice sort of faded away during the second half of 2008.

As many of you know, there are craters formed by impact of meteors and asteroids and comets on the various planets, moons, and also on asteroids and comets all over the solar system. And scientists, when they study these planets and moons and things, they really like craters because they tell us a lot about the object on which they occur. One of the things craters are good for is that they're great probes of what lies beneath the surface. The impact occurs, and the stuff that was once below the ground is now nicely exposed so we can observe it with our cameras and spectrometers and our other instruments from above.

What we found on Mars is the first time that we've seen places where new impact craters exposed water ice that was below the ground. And this tells us that in places where ice may only be a few feet below the ground, we can wait for new impact to occur and use them to test our various hypotheses about where we think there is ice below the surface, as long as it's not so deep that the impact won't reach it. So let's look at the first image on the Web site, image number 1, which is really a pair of images. This is an example of how we found these craters and it is also the location of the craters in image 2, which Shane will talk about shortly.

What you see here are two pictures taken by the Context Camera aboard the Mars Reconnaissance Orbiter. The first was taken on June 4 of last year, the second was on the 10th of August, a little more than two months later. And what you see is that something changed. In the August 10 photo, you see a cluster of dark spots. We immediately thought that this might be a new impact site, a place where an incoming meteor, in this case, may have broken up into several pieces and made a number of craters at this location sometime during the two-month interval between the pictures.

The Context Camera images are acquired at a resolution of about 6 meters per pixel, which is about 20 feet per pixel. At this scale, all we could see are the dark spots that were created by the disruption of the dust on the surface that surrounds the craters. The craters themselves, though, are too small, so they would have to be bigger, like 20 or 30 yards across for the Context Camera to see them. After we found the dark spots, however, we targeted our Context Camera a third time, this time centered on the dark spots, and we told the Mars Reconnaissance Orbiter's high-resolution camera team that we think this is a new impact crater that had just formed within the last couple months.

And they decided to ride along with us to get a higher-resolution picture to confirm whether there were craters present at the site. Lo and behold, not only where there craters, but these particular craters had exposed some ice. And Shane will talk more about that in a second. Now, finding new candidate impact sites like this is pretty much routine for the Context Camera team. Our images cover about 19 miles wide by anywhere from about 25 miles to 194 miles long. And we've covered about 45 percent of Mars with the Context Camera so far and about 15 percent of that planet has been repeated by Context Camera so that we can do images like you see in image 1.

The repetition allows us to look for changes, such as these new dark spots formed by meteors. Now, we also compare the context images with other pictures taken by Mars Global Surveyor and Mars Odyssey and Mars Express in order to see if any of these dark spots are new craters. We started finding new impact sites like this about three and a half years ago, actually using the cameras on the Mars Global Surveyor. That mission gave us 19 new impact sites. And before that no one had ever seen that there were new craters forming on any planet or moon.

With the Mars Reconnaissance Orbiter we continued the effort starting with Global Surveyor using the Context Camera, and then informing the high-resolution camera team so that they could follow up and confirm if there are craters present. And now we've gone from the 19 sites we saw with Global Surveyor to now we have 100. And out of those 100 there are these 5 that we've identified that had ice in them last year.

Now, most of these craters are very small, they're only a couple of yards across, so maybe 10 or 20 yards, and the meteors that would form these are roughly 10 times smaller than that, so the very smallest craters would be formed by rocks that are only several inches across. And with that I'll turn it over to Shane to talk about the ice in the craters.

Shane Byrne: Thanks, Ken. Good afternoon, everybody. So Ken just described the strength of the Context Camera team, and they're actually a great complement to those of MRO's high-resolution camera, HiRISE, which is what I work with. And it was with using these HiRISE data that we're able to see that these craters had unexpectedly excavated this icy material. And it was the repeat images that we took that showed that this ice had ablated away over the course of the Martian summer.

So these craters turned out to be not ordinary craters at all, which was very exciting for us. The observation showed us that this buried ice on Mars is much more extensive than we thought, but also that the ice is a lot purer than we thought. It turns out that this ice is likely to be almost completely pure or maybe contain only about 1 percent of dirt. So like I said, we were able to make these observations of the crater with the HiRISE camera.

And whereas the strength of CTX is covering vast areas of terrain at about 20 feet per pixel, HiRISE covers a smaller area, but its resolution is about 20 times better, at about 1 foot per pixel, so we can clearly resolve objects, say the size of an open umbrella or something slightly smaller. The central -- 20 percent of each HiRISE image also is taken in color, which makes it much easier to distinguish different materials. And this ice has a very characteristic color, as we'll see in the first image.

So if we turn to image 2 in the press material, you'll see that new cluster that Ken described, but a very small portion of it as pictured by HiRISE. The first of these images was taken on September 12, so just two to three months after the formation of this cluster. So instead of seeing just regular clusters, we saw something that we'd never seen before. Some of these small craters have this bright bluish material that you can see there, which we interpreted to be ice. And that bright blue material faded away over the course of the Martian summer.

This sequence of images was taken over about 100 days or so. The individual craters that the ice is in are three to four meters across, which is about 12 feet or so, so that's the size of a smallish office room. And the individual patches of ice inside that are probably about the size of your office desk. So these are quite, quite small features. They're also only about half a meter deep, or about a foot and a half deep. So if you were standing inside one of these craters, they would only be about knee-deep or so.

Over the course of the summer, the Context Camera team found several more of these impacts at high latitude. And when we, again, pictured them with HiRISE, we could see, again, that there was ice exposed in those craters as well. So another four craters turned up. And picture 3 on the Web site shows an example of one of those other craters which we found. Again, this crater in picture 3 is -- slightly bigger this time, about 6 meters across, about 18 feet or so.

So the ice that's dredged up or excavated onto the surface by these impacts is only stable in this area of the planet and sublimates away -- what I mean by that is it turns directly from a solid into a water vapor gas that drifts away into the atmosphere. So this ice fades  away pretty quickly, and it was only really the fast turnaround and coordination between the instruments onboard Mars Reconnaissance Orbiter that allowed us to make this discovery. Over the latter half of 2008, we discovered and followed up on five of these impacts. The picture, image 4, on the Web site shows the location of those various sites.

The color scale here is what's interesting. And this is, from a computer model, the expected depth to where the ice on Mars is. So the way that ground ice forms on Mars is that water vapor from the atmosphere diffuses into the soil and when it gets down to a certain depth, it becomes cold enough for that water to freeze out as ice. The small amounts of ice start to form in between the individual soil grains. So you end up with a 50/50 mix of dirt and ice below a certain depth. And you'll notice from this figure that all of these impact sites, or at least sites 1, 2, 4 and 5, are right on the edge of this area where we expect buried ice to be stable.

The gray areas at the bottom of the picture, which is in the south, show areas where ground ice is not expected to be stable. So the wetter or the more humid the Martian atmosphere, the more extensive this area of stable ice is. So based on the locations of these craters and the fact that they exposed ice, we're able to say something about how much water vapor was in the Martian atmosphere recently. And that turns out to be a lot more than what's in the atmosphere today, maybe almost double what's in the atmosphere today.

So we were able to conclude that this ice is a relic of a previously wetter climate. Now, something else that was very unusual about this ice was the fact that it was so pure. I mentioned that it was maybe 99 percent pure. That's nothing like the 50/50 mixture of dirt and ice that I just described that we were expecting. So there are a number of possibilities that maybe we can get into during the question and answer period of what might've caused that, but we were basically able to say that this ice is so pure by looking at the length of time it took to fade away.

So as ice ablates away, small grains of the soil that are suspended in the ice get concentrated at the surface and mask it from view. And the shorter the amount of time that it takes for the ice to fade away, the more dirt there must be in the ice. And since this took a really long time to fade away, we know that this ice is very, very pure. Now, it fell to the third instrument onboard MRO, our hyper-spectral imager, called CRISM, to actually confirm beyond a shadow of a reasonable doubt that this material was water ice. And so to describe that and that instrument, I'll turn it over to our third panelist today, Selby Cull.

Selby Cull: Hi. Thanks, Shane. So as Shane mentioned, these craters turned up material that was bright and white and disappears quickly, but that doesn't necessarily mean that it's water ice. Fortunately, we can easily distinguish between different minerals or different materials on the surface using another MRO instrument, the Compact Reconnaissance Imaging Spectrometer for Mars or CRISM. CRISM is kind of like the ultimate color film. While HiRISE is able to take images of dirt that's in three colors, CRISM takes images in 544 colors, where each color is a different wavelength of light. This is what's called hyper-spectral imagery, and it returns a surface's spectrum, so the brightness of the surface at each wavelength of light.

And just as it's easy for us to distinguish a warm object using a thermal camera, by looking at the thermal wavelength of light, it's easy for us to distinguish water ice by looking at its spectral signature. So the HiRISE science team found all these lovely craters and called up the CRISM team and said, hey, we found these really interesting things, could you take some CRISM images for us, and it's easy. So we did. And most of the craters are too small to show up in the CRISM images. CRISM can't resolve images that are smaller than about 60 feet.

But for the site 3 crater, where the white material is spread across the deposit, we saw a beautiful water ice spec signature, just crystal clear, no doubt about it, water ice. And you can see this crater in image 5 on the Web site. And just for reference, that image will cover about 9 CRISM pixels, so 3 across and 3 high. What's even better about the CRISM analysis is that by comparing the CRISM spectra to model spectra of water ice that's been mixed with various amounts of dirt, we can estimate how dirty the ice is. At site 3, the ice is very pure.

There's not a lot of dirt mixed in, meaning that this ice wasn't just filling in the pores of rock. It was a solid layer of ice. This fits very nicely with the thermal models that Shane was just talking about, which means that we have a pretty consistent story. The kind of scientifically heartbreaking aspect of this work is that these craters are located very close to the Viking 2 Lander Site, which landed on Mars in 1976 and dug a trench about four to six inches deep.

So now what this new study is telling us is that if Viking 2 had just been able to dig down a few more inches, it would've hit ice. And that would've been a major discovery for our understanding of Mars. It was just literally inches away from our robotic fingertips. And instead it's taken more than 30 years to finally make this discovery. So with that I'll turn it back over to Jane.

Jane Platt: Okay, thank you to all of our panelists, and, Selby, I need to apologize. I apparently botched the name of the instrument. I called it the Compact Renaissance Imaging Spectrometer for Mars and it should've been Compact Reconnaissance Imaging Spectrometer for Mars. So sorry about that. Okay, now we're going to start taking questions from reporters, and, again, if you do have a question, please press star one, and you'll give the operator your name and your affiliation so that they can put you in the queue. Let's take our first question from Jim Roop of CNN Radio. Jim?

Jim Roop: Hi, thank you very much. First of all, I'm a general assignment reporter, I'm not a science reporter, so forgive me if my question seems juvenile in its construction and if my understanding seems juvenile, too. I'm going to ask you to clarify if I don't understand. You've got to talk to me like I'm a 6-year-old. Does this mean then that throughout the planet of Mars, there may have been rivers or oceans and things like that, that now it's ice because of climate change of some kind?

Shane Byrne: This is Shane. I can take a crack at answering that. It means that Mars had a more humid atmosphere in the past, but probably not that there was actually liquid water in the recent past. So when I'm talking about recent here, I'm talking about maybe 10,000 years ago or so. And while Mars may have had a lot of liquid water in its history in the more distant past, the last period of Mars's history, which this ice is representing, has been very, very dry. So one of the reasons why the ice is so unstable when it gets dug up by these craters is that the Martian atmosphere is so dry. So although we've shown that the Martian atmosphere was a lot wetter in the recent past, it still wouldn't be enough to support liquid water on the surface.

Jim Roop: So what does this mean, then? I mean, why is this significant to study?

Shane Byrne: Well, it shows that the climate of Mars has been changing over the recent past and that Mars' atmosphere has been drying out and that ice is being lost from these midlatitude areas and probably being put back on the polar caps. Now that goes both ways. I mean, some other periods in Mars' history, ice is coming off the polar caps and is being put in the midlatitudes. And in some more extreme climate changes, potentially a lot of ice is moving around like that. So with a lot of water ice moving around like that, there's the potential further back in Mars's history for that ice to maybe form snow packs against the sides of craters or on debris aprons, which can later flow like glaciers. And that snow can possibly melt, but much further back in Mars' history than what we're talking about now.

Jim Roop:Why do we need to know this? What's the significance with Earth?

Shane Byrne: Well, you could compare this to climate change on the Earth, except that perhaps on Mars things are a lot simpler than on the Earth. So on Mars the only thing that's changing really is the amount of sunshine that goes in and out of the planet, and the planet's orbit changes a lot compared to Earth, so that gives us a way to maybe examine how the effects of just variations in sunshine affect climate. On the Earth, it's a much messier system with oceans and with life and with the effects that humans have on the climate, and that's really hard to untangle everything. But on Mars we have this very simple system, so trying to understand how that simple system works can eventually help feedback into our understanding of Earth's climate in the long term.

Jim Roop: Great. Thank you very much.

Jane Platt: Okay. Thank you. And the next question is coming from John Johnson with the LA Times. Hi, John.

John Johnson: Hi. So that answered part of my question. I just wanted to factor into what we knew already about -- or thought we did anyway -- about Mars' climate. In the material it talks about this now showing that it was wetter more recently than we had thought, but I gather from what you're saying that it wasn't wet enough more recently to be of any use in terms of a warm place where any kind of life form of any size could have developed.

Shane Byrne: Right, that's right. So this ice is kind of a double-edged sword because this ice is in a region which changes very sensitively when climate changes. So in that respect it's useful because it allows us to talk about what happened most recently in Mars's history. But in another respect it's maybe not so useful because everything in recent Mars's history hasn't been damp enough to support liquid water on the surface. So we're looking at a slice of Mars' history that is very recent and doesn't refer back to these periods on Mars where we may have had liquid water.

John Johnson: So it just adds another chapter to the climate story, then?

Shane Byrne:Right. This is like us going back and filling in chapter one.

John Johnson: Okay. Thank you.

Jane Platt: All right. Thanks. And our next question from CBS News, Bill Harwood, hi.

Bill Harwood: Yes, hi, thank you very much. Can you hear me, okay?

Jane Platt: We hear you fine.

Bill Harwood: Thanks. I've got two quick questions. One's a simple one, and one's a dumb one. The simple one, is there anything in this that lets you extrapolate to -- I mean, are we talking isolated deposits? Are we talking broad sheets of buried ice? I just was curious how this stuff manifests itself below the surface.

Shane Byrne: This is Shane again. I can take a crack at that as well. Every indication is now that this is forming a broad continuous sheet underneath the surface. We have five separate impact sites all showing more or less the same thing. And also we have results from the Phoenix Lander, which touched down recently and excavated ice much further north, much nearer the polar cap. But they also found patches of clean ice that was, for all intents and purposes, almost pure ice, so there's a consistent picture starting to emerge now that these broad sheets of ice may be common on Mars.

Bill Harwood: And is there also any way to extrapolate or make even an educated guess as to the volume of water you're talking about? I realize this is a limited dataset, but just to kind of put it in context.

Shane Byrne: Yeah, I'd say the volume of water, and this is a guess, and the exact numbers I can give you later after the telecon, but the volume of water is probably comparable to the volume that we would have in say the Greenland ice sheet on the Earth, in the buried ice deposits that stretch from each pole to the midlatitude in each hemisphere.

Bill Horowitz: Thank you.

Jane Platt: Okay. And, Bill, if you did need some follow-up afterwards, just call Guy Webster at JPL or Dwayne Brown at NASA headquarters and I'll be giving those phone numbers at the end, but I think you have them already, probably. Okay. We're going to take our next question from Tariq Malik of space.com.

Tariq Malik: Thanks. This is Tariq Malik from space.com and Space News. And I think my question is to follow up on Bill's to Shane. When you compare the volume, I guess, of the ice distribution that you're looking at now on Mars to that Greenland ice sheet, is it possible to estimate in terms of tons, and how surprising is it to have such a wider distribution now further south towards the equatorial areas than, say, Phoenix's landing site near the pole?

Shane Byrne: In terms of volume, the indications from these impact sites are that there's a clean layer of ice that's probably about 1 meter thick or so. And these ice sheets that extend -- these buried ice sheets that extend from the poles all the way down to 45 degrees or so don't quite cover half the planet, but come close to covering half the planet. So we're talking about maybe a million cubic kilometers of ice, in total.

Tariq Malik: Great. And I guess that distribution, I'm just curious as to your reaction to finding such a wider distribution than perhaps you'd previously thought and the fact that it's so pure -- I mean, how much of a surprise was that for you and your team?

Shane Byrne: The purity was a great surprise because we expected it to be a 50/50 mix of ice and dirt. And that turned out to be about as far from the truth as you could imagine. This is pure ice. So the candidate mechanisms for forming this pure ice layer are not especially convincing, but the two main theories are -- one that it was snowfall that occurred maybe about 400,000 years ago on Mars, would be the last climatically favorable time for that to happen. And we would expect this ice to have come and gone many times in that intervening 400,000 years.

So although this could be buried snow, that is not a very satisfying explanation. The other explanation that's possible is that this is a process that we call frost heave on the Earth. And frost heave works by having thin films of liquid water around the ice crystals, and that liquid can move and basically form these ice lenses. So liquid migrates to a cold part and starts freezing out a pure ice lens. So having liquid water, even though it's very thin films, having liquid water on Mars would be of great interest, possibly for biology or chemical alteration of the soil. So although this process is common on the Earth, we weren't expecting it to be on Mars, if indeed it turns out to be this process.

Jane Platt: Okay, thank you, Shane and thank you Tariq. Our next question -- and I do want to remind you that if you do have a question, just press star one, and the operator will get your name and affiliation and you put in the queue to ask your question. Next we'll go to Irene Klotz of Discovery Channel.

Irene Klotz: Thank you very much. I have two questions. The first is does this discovery shed any light about what happened to Mars's atmosphere? And the second question is do you think that these findings in any way should or could tweak the ongoing exploration plans to Mars? Thanks.

Jane Platt: Anybody like to jump in? Well, maybe we'll call on -- we have here with us at JPL Sue Smrekar, who's the deputy project scientist for Mars Reconnaissance Orbiter. Do you want to take a stab at that, Sue?

Sue Smrekar: Okay. So in terms of future missions, our next mission in the queue is aimed at looking at the early history of Mars, so the water that's found in minerals that formed more like a billion or 1.5 billion years ago. So not immediately, but I wouldn't be surprised if people attempt to follow up on this discovery and try to better understand the history of this ice that is at higher latitudes. So it will take a while for people to come up with suggestions to follow up, but it's certainly a possibility. I think there was another part that I missed.

Jane Platt:Yeah, what was the other question? Could you repeat it?

Irene Klaus: Yes. I wanted to know if anybody had any idea if this answered some questions about what happened to Mars' presumably past thicker, wetter atmosphere. Does this shed any light on the process by which that atmosphere seems to have disappeared? Thanks.

Sue Smrekar: So the water that was present early on in the history of Mars -- the question is has it been lost to space or is it still buried at depth on Mars? And this particular find doesn't really address that question because this water is in equilibrium with Mars's recent atmosphere. So early on in the history of Mars there might've been much more water, but this particular find doesn't help us address that question except in the sense that it helps us better understand climate evolution overall on Mars. But it's really focusing more on the recent history. Does anyone else want to add to that?

Jane Platt: You don't have to, but . . .

Shane Byrne: This is Shane. I think that covers it, Sue. I'd just add that we can use this information on the last 10,000 years or so that we're gaining to help extrapolate more reliably back into the past on what the climate may have been like further back.

Jane Platt: Okay, thanks, Shane. And thank you, Sue. Let's go now to a question from Leo Enright of Irish Television

Leo Enright: Thanks, Jane. I was just wondering if there's anything that you're seeing in perhaps the context imagery that would be diagnostic of this. I understand it's a thin sheet of ice, but we have seen obviously things like lobate flows where they're postulating glacier deposits and also these ice rafts that have been seen. Is there anything even hinting at a diagnostic in the topography that might help in looking for -- to map this?

Ken Edgett: This is Ken Edgett. First of all, in terms of diagnostic things, if you were to look back at image 2, you can actually see that the terrain has these polygons, and on the Earth, typically, that would be related to ice in the ground. And so in a place where you see those polygons, now we know that we might expect to find ice in a fresh, brand new crater like this. These other features you're talking about, like these aprons that people have proposed have ice in them based on radar observations or other features that occur at other latitudes, lower latitudes than this, on Mars, there's nothing we can do that's diagnostic yet. But what you can do is watch for new impact craters like this to form, and if the ice is shallow enough relative to the surface and the new crater forms and then you see that ice, then you have tested that hypothesis and found it to be having ice.

Leo Enright: My other question was about the southern hemisphere. I mean, what about the Hellas Basin and places like that? Have you been looking and would you expect to see something similar in the lower-lying highlands of the south?

Ken Edgett: The fun part about the southern hemisphere is that, yes, we're looking, but it's harder to find these impact sites. These craters are so small that what we're relying on is that the impact event had to disrupt enough dust near the crater in order for it to show up in the Context Camera images, right? Because the high-resolution camera can't cover the surface area. The Context Camera can, but it can't always see the crater unless it's very big. So we're looking for these dark spots.

It turns out these dark spots are only showing up in the most dusty regions of Mars, and those are almost entirely all in the northern hemisphere. In the south, however, you're right. Hellas and the Argyre Basin as well do have dusty surfaces, and we've been looking there. And we've also been looking at over 600 sites in the southern hemisphere midlatitudes that we image repeatedly to look for changes in gullies. And we have not yet found fresh craters that have exposed ice in any of those attempts. The other thing we've found with Argyre and Hellas is that things are changing down there so quickly, the dust comes and goes, and there's frost in the winter and things, that when you do have a new crater in one of those basins, the dark spot usually disappears in less than a year's time. So we don't always get to find these things.

Jane Platt: Okay. And next question will be from Peter King of CBS Radio.

Peter King: Thanks, Jane. And congratulations on the discovery. The one thing that absolutely I find absolutely stunning is that some of this has been almost under our noses since 1976. And I want to know how close to the Viking 2 spacecraft landing site was the closest ice found and how do you feel about having been so close for so long?

Ken Edgett: Selby, go for it.

Selby Cull: All right. Well, it looks like the Viking 2 Lander was about 350 miles or so from the site 3 crater, which is the one in which CRISM has the distinctive ice signature. And certainly we would have liked to have had that information about Mars for the last 30 years. I don't know how that would have changed our perspective, but it certainly would've.

Jane Platt: Okay. Thanks. I'm going to do sort of a last call, if anyone does have any questions, we have time for a few more. So press star one if you have a question and ID yourself to the operator and we'll call on you. In the meantime, we will get a question from Charles Fishman of Fast Company Magazine.

Charles Fishman: Good afternoon. Do you guys have a sense of where this water came from, where the water ice -- where the water that formed the ice came from? Is this part of the original formation of Mars? Did the water come to Mars in some other way? Is there any way of knowing how the water got to Mars in the first place?

Shane Byrne: This is Shane. I'll try to answer that. So Mars started off with quite a lot of water on its surface, and that water has gradually over time, as Mars has gotten colder and dryer, been concentrated at the polar regions. So right now at the polar regions we have big icecaps that are a couple of miles thick and maybe a dozen miles across. And as Mars's orbit changes all the time and its climate changes all the time, that ice sometimes gets pulled off the polar cap -- it gets ablated off the polar cap, and it gets then placed in lower latitudes, like where these craters are now. And then as the Martian climate swings back, that ice gets pulled out of the midlatitudes and put back on the polar caps. So the ice is constantly doing this back and forth with the polar deposits.

Charles Fishman: And you guys are pretty confident there was a lot more water at some point? So that water was part of the original formation of Mars?

Shane Byrne: Yeah. I guess -- small amounts of water have been delivered over the last 4 billion years through comets and things like that, but most of the -- the vast majority of the water that is there on Mars today was there -- or had been there for a very long time.

Jane Platt: Okay. Our next question comes from Marcia Freeman at 21st Century Science.

Marcia Freeman: Yes, thank you very much. I think I might've missed something. Perhaps you could clarify this. What in the data that you're discussing gives you the history? You said you can go back 10,000 years or you have some indication that the ice that you're seeing goes back that far, and somehow I missed that marker.

Shane Byrne: Okay, this is Shane again. The number 10,000 years from simulations of what we'd expect ice to be doing on Mars. So to have ice at these locations, we need to adjust the amount of atmospheric water in these computer simulations to be able to match that observation. So that's the observational part of it. These simulations, then, when you run them backward through Martian time tell us when this area was last ice free.

And ice in the midlatitude regions reached its southernmost extent about 10,000 years ago. And over the last 10,000 years, it's been retreating backwards and going towards the poles. So this ice that we see today is a relic from that era and is still in the process of retreating away and getting put back on the north polar cap, although it's doing it much more slowly than we expected.

Marcia Freeman: Thank you.

Jane Platt: Okay. All right. Thank you. And we're going to go back for a couple of follow-up questions, first to CBS News and Bill Harwood.

Bill Harwood: Yeah, thanks. I just want to make sure I understand a little bit more about what you're talking about. Is the surprise today the purity of the ice that you found? Is that the major surprise? Is it the closeness of this ice sheet to the surface? Or is it both? I'm trying to understand what you knew before versus what you know now. Thanks.

Shane Byrne: Okay, so there are two main conclusions to the paper. One is that the ice stretches further towards the equator than what we thought before, which tells us that Mars's climate has been wetter than what we thought in the recent past. And the second major conclusion is that this ice is virtually pure, and we were expecting this mixture of 50 percent ice, 50 percent dirt. And having that pure ice there means that something very unusual could have happened on Mars that we weren't expecting at all, like possibly this frost heave mechanism where that might involve small amounts of liquid water.

Ken Edgett: This is Ken Edgett. I'll jump in, too. For me the surprise was that this would happen at all, that you could get a brand new impact crater and that it would hit ice that's beneath the surface, bring it to the surface, that we would see it before it all sublimates away, and that we could monitor it for a few months while it goes away. That's not necessarily the science result, but it is pretty darn cool and surprising.

Selby Cull: This is Selby. If I could just add something to that as well. The Phoenix mission on the other side of the pole turned up two different kinds of ice. It turned up this very pure ice that we see now and also the more 50/50 percent dirty ice that we were expecting. And during the Phoenix mission, without this new data, we assumed that the pure ice was the anomaly, and we were all speculating how could this possibly have formed.

And now we see on the other side of the pole multiple incidents of very pure ice being exposed. So it looks like the pure ice is the rule and that this little bit of dirty ice that we found with Phoenix is actually an anomaly. So this is sort of typing up some of the loose ends from our Phoenix mission, which is always a fun thing to do.

Jane Platt: All right. Thank you, Bill. And thank you, panelists. And let's go to a follow-up question now from space.com and Tariq Malik.

Tariq Malik: Thank you. I think I had a question for maybe Sue. It's just a cleanup question because obviously these findings are great from MRO, but I know there's been some work to get it back to health. If you can give us an idea of how that work has been going so that it can kind of resume these observations, that would be great. Thanks.

Jane Platt: Okay. And we have with us here at JPL Jim Erickson, the Mars Reconnaissance Orbiter project manager, so I'm going to call on him now.

Jim Erickson: Okay, we are resting comfortably in safe mode right now while we investigate the series of safe modes we've had over this entire year. There's been four of them. We are concerned that we've had such a large streak. We are working hard to identify exactly what's going on there. We've identified that there are some issues that we think we need to fix in the short term, and we're working hard to put protection against those concerns onboard right now.

We expect to do that in the next few weeks while we continue in parallel to investigate the root cause of what these anomalies are. I feel confident we're going to get the spacecraft back up and running soon, but I don't want to speculate on exactly when. Our priorities are keep the spacecraft safe, figure out exactly what's going on, and make sure it's productive in the long term.

Jane Platt: Okay. Thank you, Jim. And it looks as though everybody who had a question has had their question answered. If you think of anything afterwards, two options. This telecon is being archived for one week, actually, until October 2, and you can access it any time probably starting about an hour from now by calling 1-866-396-4180, or international callers 203-369-0506.

And this information is also on this Web site. And if you do have any additional questions, contact either Dwayne Brown at NASA Headquarters at 202-358-1726 or Guy Webster here at JPL Media Relations, 818-354-6278. And we do also have a NASA TV video file on this topic airing today. I want to thank our three panelists who are on the line and Jim and Sue who are here with us at JPL. Thanks everybody for joining us, and have a great day.