Astronomy Cast

Ep. 91: The Search for Water on Mars

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With the successful touchdown of the Phoenix Lander, NASA is continuing its quest to find evidence of past and present water on Mars. This week we discuss the geologic history of Mars, and explain why NASA thinks the story of water on Mars is so important. And how this ties into the search for life on the Red Planet.

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AstroCast-080602.mp3

Speaker 1 [00:00:00] This episode of AstronomyCast is brought to you by Swinburne Astronomy Online, the world’s longest running online astronomy degree program. Visit astronomy .swin .edu .au for more information. 

Fraser Cain [00:00:19] AstronomyCast, episode 91, for Monday, June 2, 2008, the search for water on Mars. Welcome to AstronomyCast, our weekly facts -based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. My name is Fraser Cain. I’m the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University, Edwardsville. Hi Pamela. 

Pamela Gay [00:00:44] Hey Fraser, how’s it going? 

Fraser Cain [00:00:46] Good. Well, as we now talk to people, I guess as we talk right now, you’re at the AAS meeting, and I unfortunately wasn’t able to make it, but I’m sure you’ll be reporting plenty from it. So I guess everyone should just stay tuned for that. 

Pamela Gay [00:01:02] We’re going to have a ton of coverage all over the meeting. We’re going to use Ustream. We’re going to be live blogging on AstronomyCast Live. We have twisted the arms of a bunch of friendly souls to join us, and we’re doing a meetup. If you hear this before Tuesday night and you live in the St. Louis area, we’re going to be at Kitchen K starting at 7 p .m. It’ll be me. It’ll be Phil Plait. It will be Chris Lintott, Michael Kopelman. Every blogger and podcaster we can find, we’re going to invite to join us, and we’d love to see you. 

Fraser Cain [00:01:38] All right. And thanks to everybody who tried to set up our Wikipedia entry last week. Apparently the Delete Brigade is in full effect. We got emails from about four or five of you who tried to set up a Wikipedia entry for AstronomyCast and said that it got deleted almost immediately by someone who said that it was advertising. So apparently it’s a big controversy right now. I guess we’ll have to lay low until until that gets figured out. OK, well, let’s move on to the show. And this is probably our next three shows are going to be all about Mars. Just to celebrate the Phoenix Mars lander, we thought we’d do a bunch of Mars episodes. So this one is going to be about the geology and the search for water on Mars and how this ties into life. So with the successful touchdown of the Phoenix lander, NASA is continuing its quest to find evidence of past and present water on Mars. This week, we discuss the geologic history of Mars and explain why NASA thinks the story of water on Mars is so important and how this ties into the search for life on the Red Planet. All right, Pamela, we got to talk about geology and we got to talk about water. 

Speaker 3 [00:02:53] Where do you want to start? Let’s start with rocks. 

Pamela Gay [00:02:56] Let’s start with the geology of Mars. All right, you can start with geology. What should we all know? So the best place to probably start is with its size. Mars is a lot smaller than I think most people realize, or at least most people who haven’t read a lot about Mars. It’s about half the radius of the Earth and one tenth the mass. And this means that you can actually say, since size is in a well -defined word, that it’s one tenth the size of the Earth. It’s actually very low density. It’s so low density that its combination of radius and mass means that standing on the surface of Mars, I would weigh less than if I stood on the surface of Mercury. And that’s just kind of cool. It’s Mercury is this high density little world, smaller radius. It’s just the way all the ratios work out. So you have this little tiny planet, and because it’s small, it can’t hold on to its heat. It’s just like a really skinny person. They get cold very easily because their heat can radiate away quickly. There’s not a lot of skin to hold in all of that heat. Well, with a small planet, a small planet also, it cools off quickly and it can cool all the way to its center quickly, which is one of the keys with Mars. Mars didn’t have plate tectonics like the Earth. Here on Earth, we have plates that are trying to move. This is unfortunately what just caused the really devastating earthquake in China. And these moving plates, where they rub up against each other and move away from each other, they sometimes allow heat to escape. Well, Mars didn’t have any way for the heat to escape like that. So in different places, lava, magma burst through the surface in huge amounts, and it just kept coming out and kept coming out. And this radically shaped the surface of Mars, creating both the largest mountain in the solar system, Olympus Mons, and the largest valley in the solar system, Valles Marineris. Olympus Mons is 26 kilometers high. It’s so tall that Mars’ surface curves away fast enough that you can’t see the top of Olympus Mons when you’re standing at its base. And when you’re standing at its surface, you can see tens of kilometers in distance, just across the top of the chasm that is the pit that makes the volcano look like a volcano. 

Fraser Cain [00:05:31] Now, let me see if I can just wrap my head around this a bit. You know, here on Earth, we have the plate tectonics, and this is where we have these plates going underneath one another or rubbing side to side from each other. And so these are kind of a function of the size of the Earth and the way it’s cooling down. Is that right? And so they’re able to let off the pressure and let out the magma in smaller amounts. But like on a place like Mars, and I know Venus is kind of similar, that for some reason, Venus just hasn’t had plate tectonics for billions of years. And so all the volcanism that ever happened on Venus is still visible on its surface. 

Pamela Gay [00:06:17] So there’s three variables that allow you to have massive, gorgeous plate tectonics with the volcanoes that come with it, with the rift valleys that come with it, with all the neat things that allow us to look at our planet and say, we can see our surface changing. And those three things are you have to have heat inside the planet. You have to have water to lubricate the motion of those plates. And you need a way to hold on to that heat for a prolonged period of time. Otherwise, the plate tectonics really just don’t have time to do anything really cool. 

Fraser Cain [00:06:57] Right. But you can’t have too much heat either. 

Speaker 3 [00:07:00] Exactly. 

Fraser Cain [00:07:00] Which is the problem I know on Venus. 

Pamela Gay [00:07:03] Its water went away. 

Fraser Cain [00:07:04] Right. Right. Yeah. So you get too much heat in the water. Because I know I did an article just a couple of weeks ago where people calculated that if the temperatures got high on the Earth, you know, like by another 100 degrees Celsius, plate tectonics would probably shut down on Earth. 

Pamela Gay [00:07:23] It’s all a matter of needing this water to be a lubricant to allow the plates to move. And for whatever combination of these reasons, Mars never really developed plate tectonics. 

Fraser Cain [00:07:35] So that’s a strike against Mars for water, right? No plate tectonics, maybe no water. 

Pamela Gay [00:07:41] Well, we know it has water. This is where it’s the combination of variables that matters. The big thing with Mars is its temperatures cooled off such that about 3 .5 billion years ago, there was a massive heat release. And after that, the planets just sort of been sitting there going, Hi, I’m here. So when we look at the different epics of geological stuff going on on Mars, you start with the Noachian epic. It was the period of time when the oldest surfaces on Mars were formed. It went from about 3 .8 billion years ago to 3 .5 billion years ago. This is when the Tharsis Bulge volcanic uplands. The big, gorgeous set of volcanoes that form pox marks on the side of Mars uplifted and began to form. Now, there was also at the same period of time, extensive water erosion across the surface of Mars, where we can see fossilized in the rocks, basically, because there’s nothing there to do additional erosion other than craters and dust. And they’re just not effective as a well, craters are effective, but dust is not effective. 

Fraser Cain [00:08:58] You know, with Mars forming at the same time the Earth forms, that’s like 4 .5 billion years ago. So this is like a billion years after Mars formed. We’re not able to see any time before that just not that we’re able to recognize. 

Pamela Gay [00:09:14] And part of this has to do with the early eight parts of the solar system. There was so much bombardment going on right that this is where craters are effective at erosion. 

Fraser Cain [00:09:25] Really, really. So there was so many craters, so many asteroids slamming into the surface of Mars that it was getting resurfaced as good as plate tectonics. 

Pamela Gay [00:09:35] Well, and there may have been plate tectonics at this earlier period. So for a combination of various reasons, we can’t date any part of the Mars surface. Admittedly, we haven’t exactly gone there and walked all over it. We’ve only seen very limited areas that our rovers have been able to explore. But as near as we can tell, we can’t date surface features as being older than 3 .1 billion years. But from about 3 .8 billion years to 3 .5 billion years, there was the formation of the Tharsis Bulge. And what was cool is at the same time, there was flooding by liquid water. And we’re able to date these streams by the number of craters that overlap riverbeds, streambeds, other we call them falluvial formations on the surface of Mars. 

Fraser Cain [00:10:21] Right, the good old craters, count up your craters, and that tells you how old a chunk of landscape is. 

Pamela Gay [00:10:30] And then beyond all of this wonderful liquid water destruction of the surface formation of riverbanks and neat things like that, we have the Hesperian Epic. This was about 3 .5 billion years ago to 1 .8 billion years ago. And this is when there were lava planes formed. So there continue to be different shield volcanoes. There are dozens of different types of volcanoes on Mars. And what’s really cool is you can look at pictures of some of these volcanoes on Mars, and then you can compare them to different structures all over the planet Earth, and they look the same. And we can look at these volcanoes on Mars, and in some cases, they’re just small rifts in the side of a hill that lava has spilled out forming what we call tongue -like forming, well, tongues of lava. There’s actually, and I have this blogged about on my blog. We’re both plugging our blogs tonight, I guess. There’s a lava flow that is in New Mexico. It actually cuts across white sands. And it is exactly the type of lava flow that you’d expect to see on Mars. And so we can study in detail what it looks like on Earth, and then use that knowledge from our own planet to better understand the surface of Mars. So during the Hesperian epic, there were vast lava planes formed. Again, we can date this from the cratering. Then beyond that, there was the Amazonian epic. And I’ve always found it odd that to me Amazonian evokes ideas of rainforest, but the water wasn’t during the Amazonian epic. 

Fraser Cain [00:12:13] Yeah, I think water here. 

Pamela Gay [00:12:14] Yeah, no, the Amazonian epic. This is the most recent period. This is when there really wasn’t water to be found on the surface. And so this recent period from 1 .8 billion years ago to present is basically marked strictly with, well, impacts happened. But other than that, this is the period when Olympus Mons finished forming. But other than that, not much happened. All right. 

Fraser Cain [00:12:49] So when, like I know we talked, you talked about in the earliest, in the Nokian epic, there was water flowing. So what’s kind of the theory on what role water played on Mars in the past and up to now? 

Pamela Gay [00:13:04] Well, today, let’s let’s start with today and work our way backwards. The problem with Mars is because it’s so small, the pressure that water experiences from the atmosphere when it’s on the surface of Mars causes the water molecules to instantly go into a gaseous state. So you can have water ice where the molecules happily bond onto each other and form nice crystalline structures. Or you can have water gas, but the liquid state just ain’t going to happen. 

Fraser Cain [00:13:38] So if I put a cup of water out on the surface of Mars, it would just boil away. 

Speaker 3 [00:13:43] Yeah. 

Pamela Gay [00:13:44] And it’s like watching liquid nitrogen here on the surface of the planet Earth. If you’ve ever had a chance to see it, you normally store liquid nitrogen in specialized containers that help keep it under pressure. When you release it in an atmosphere, it just starts boiling. There’s not enough pressure on it to hold the molecules together. And water on Mars acts the exact same way. There’s not enough pressure on the water to keep it liquid. So it just evaporates away. But it actually will avoid the liquid state altogether if you let it. If you take a chunk of ice, put it on the surface, warm it up during the Mars summer, it goes straight to gas. 

Fraser Cain [00:14:29] That is not good for life. 

Pamela Gay [00:14:32] No, no, no, it’s not. All right. 

Fraser Cain [00:14:35] And so what do we see today then? Because I know there’s water there right now. 

Pamela Gay [00:14:39] Well, what we think is if you go beneath the surface of the planet, and different people have come up with different amounts of how far beneath the surface you have to go, whether it’s a few tens of centimeters or more than that, once you get below the surface, you start getting into situations where salty water, which is a little bit harder to make, we call it sublimate when it goes from ice to gas, it might be possible for very briny, very salty water to exist beneath the surface, not too deep under the surface. And there could be life there. There’s also caves that might be able to protect life. And we don’t think life natively came about in this sort of an environment. But we have this clear evidence that for at least a brief geological period in the past, there was liquid water in large amounts and probably rainstorms and other normal hydrological events on the surface of Mars. And the water that allowed all of these things to happen was the water that had previously been trapped in the crust. It’s thought that when the planet was going through a huge heat release, part of all of the volcanism that was going on, that this released a lot of the deeper water and allowed it to have atmospheric water for a period of time that was sufficient to form clouds, that was sufficient to rain, that was sufficient to form rivers. Details, no one really knows the details. 

Fraser Cain [00:16:18] Right, but how do we know this? 

Pamela Gay [00:16:22] We know it by looking at the riverbanks, the streambanks. There’s certain features that you can try and explain away with, well, if dust blew on it for enough thousands of years and we know that Mars is dusty, we can see the dust storms from the planet Earth. Whenever Mars makes its closest approach to the sun, it has, in some cases, planet -wide dust storms. But when you do the mathematical modeling, yeah, the dust is really bad. It mucks up the solar panels on our little rovers. It’s just, who wants to be in a dust storm? But it’s not enough to cut away all the rivers. It’s not enough to cut away all the streambanks. 

Speaker 3 [00:17:07] That took water. 

Fraser Cain [00:17:09] Right, but I know that spirit and opportunity found evidence, found what we needed, right? 

Pamela Gay [00:17:14] So the other evidence comes in the different minerals that form. There are specific minerals that can only form in watery environments. One of the coolest examples that many people are probably familiar with is a rock called hematite. If you go to a random mall here in America, there’s often kiosks that have little bracelets made out of these rounded stones that look sort of like liquid mercury. And that stone is called hematite, and it forms in water. And there’s whole planes covered in hematite on the surface of Mars. So all these different minerals that we’re finding, we’re sampling, we’re making sure, yeah, we’re exactly, positively right that these are these specific minerals. They required wetness to be there when they formed. 

Fraser Cain [00:18:06] So the evidence has been found that water acted on the surface of Mars for long periods of time. Spirit and opportunity, I know, found some of the minerals that are associated with water. And so more evidence that at one time Mars probably had oceans or seas or something. So that’s hopeful for life. So how does Phoenix play into this? 

Pamela Gay [00:18:32] Well, one of the most striking features of Mars, a feature that you can actually see with a good eight inch telescope here on the planet Earth, is its pair of ice caps. Its northern cap can actually extend a thousand kilometers in diameter during the summer. And it contains about 1 .6 million cubic kilometers of ice. If this was spread evenly over the caps, and we don’t think it actually is, so it’s probably thinner in some areas than thicker in others. But if it was spread evenly, this ice would be two kilometers thick over a diameter of a thousand kilometers. That’s just really cool. Now, the southern polar cap has a diameter of 350 kilometers. It’s nowhere near as big. And this difference is actually due to the fact that Mars does change its distance from the sun more than most of the other planets in the solar system. So during its southern winter, it’s actually much further away from the sun than during its northern winter. And this causes the cap to be smaller. But these ice caps, they contain water ice. They contain dry ice. And we know that here on the planet Earth, life is capable of existing inside of ice. And if the ice is dense enough, you can get salty briny inclusions of liquid inside the ice. So there’s lots of different possibilities for places that we might be able to find organic molecules that are working towards life. We might be able to find fossils of life. Maybe we just might be able to find life itself. 

Fraser Cain [00:20:18] Well, I know that there’s another recent discovery, also blogged about on universetoday .com, where people found life microbes like a kilometer and a half underneath the surface of the ocean. So down there, you can get some serious pressures building up, and you could very well have liquid water below all the ice. And also below a lot of glaciers on Earth, there’s liquid water. So it sounds like there’s a lot of places where there might be life. So what is Phoenix going to be looking for then? 

Pamela Gay [00:20:55] Well, we’re going to talk a lot more about missions next week. But Phoenix right now, it’s doing a basic reach out and dig someone. Here, it’s going to reach out and dig a few centimeters into the surface of the ice. And it’s going to look and see what it can find. It’s going to look and see what compounds are in there. It’s going to look and see are there organics trapped? What is the ice like? It’s a little biological laboratory, and it’s going to do its own CSI -style investigation, which we’ll talk about in detail next week. Now, one thing I’d like to bring up while we’re on the topic of geology is the fact that life on the surface probably isn’t going to be something we can find. And it’s not just because of the water. It’s also because of the radiation. Mars doesn’t have an atmosphere like Earth’s, and Mars doesn’t have a magnetic field like Earth’s. And this means that solar radiation reaches the surface of the planet. And if you’re hanging out living on the surface, you’re going to be irradiated. And life does not like radiation. 

Fraser Cain [00:22:02] But get underground or into ice or under ice, and you’re protected, right? 

Pamela Gay [00:22:08] And this is where some of the newer discoveries, like the caves that were found by Mars Odyssey Orbiter on the flanks of one of the volcanoes, become so important. These caves, which have been named actually after the discoverer’s friends, family, and loved ones, are Dina, Chloe, Wendy, Annie, Abby, Nikki, and I think it’s Jean, but it might be Gina. These caves, which are so humanly named, it sounds like some sort of a Mouseketeers group more than a group of planetary formations, they’re deep. They’re in some cases a couple hundred meters wide and at least a hundred meters deep. We say at least because we can’t see the bottom of the caves. Except for one. There’s one that we know is 130 meters deep. But the rest of them, we can’t from the orbiter see the floor of the cave. So these large, deep caves, well, if you get far enough underground, the ground is going to protect you from radiation. These are places where you could have water ice. These are places where you’re protected from the radiation. These are places that it just might be that either dormant life that is waiting for a warmer day to come, which probably will never happen, or life that thrives in ice are capable of existing. 

Fraser Cain [00:23:44] Well, I think it’s a good approach. People are really chomping at the bit because they really want NASA to just find life on Mars already. But their approach is really good. Step by step, they’re following the water. They’re building up the evidence for the water on Mars, finding it at the equator and now they’re working to find it at the poles and examine it and really understand its history. And I think it’s interesting how sort of in line with that, more and more discoveries and thinking is happening about both the nature that life can take, not just water -based or other chemicals can be involved in its functions, but also just the things that on Mars that might be working against it, but also the things that might be working for it. So it’s interesting to see as the buildup is coming to some of the future missions, and we’ll talk about that next week, how the search for water is getting really intense and they’re really building a good picture. But at the same time, the understanding of what life might look like is going forward as well. And I’m almost kind of glad that they took it in this order because they have a much better idea of what to look for in terms of life today than maybe they would have back when Viking, because I don’t think Viking found anything. 

Pamela Gay [00:25:09] We’ll talk about that. 

Fraser Cain [00:25:11] But now they’ve got a much better idea of how to look for life. And some of the upcoming missions are going to be really well equipped to search for life in some pretty weird places. So I’m pretty excited about that. 

Pamela Gay [00:25:25] It’s going to be a fascinating next 10 or 20 years. We’re going to get to this in the third episode. There are actually plans to start figuring out how to put men on Mars, women on Mars. Let’s get a colony out there. 

Fraser Cain [00:25:41] Let’s terraform it. No. 

Pamela Gay [00:25:43] We’ll also talk about why that probably isn’t going to happen no matter how good Kim Stanley Robinson’s books are. It’s a world we plan to go out and walk on within our lifetime. And as NASA is moving forward with its constellation program, when it’s building heavy lift rockets, its plans aren’t just to return to the moon. Its plans are how do we build something that will help us get beyond Earth -Moon and out to the next nearest asteroid, the next nearest planet. What’s next on the horizon? And what’s next just might be Mars. 

Fraser Cain [00:26:21] Do you think that there could be ever a future for Mars where water gets back on the surface? 

Pamela Gay [00:26:27] Only in enclosed domes. The problem is that you can’t change the atmospheric pressure of a planet. Not without releasing vast, huge, giant quantities of gas. And because Mars is such a low -mass planet, any gas that you release into the atmosphere is likely to just stay a little while and then go away because collisions between individual atoms, one atom might get sped up while another slows down just like a couple of people on roller skates. One gets sped up and one gets slowed down when they collide. Their masses are too different. Well, these collisions cause atmospheric particles to reach velocities that allow them to escape to another part of the solar system. Here on Earth, we can’t hold on to our helium. We can’t hold on to our hydrogen. Every time a little kid’s balloon loses its helium, that’s helium that’s lost forever, at least for our planet. That’s so sad. It is. It’s not just the kid’s balloon won’t float. There’s one more natural resource gone. Peak helium. With Mars, oxygen can escape too. And so even if we do attempt to build an atmosphere, really we can’t. That’s not something we can do. We can change the ratios of the things in the present atmosphere, but we can’t make it thicker. 

Fraser Cain [00:27:54] Right. So you could imagine some far future where the sun is heating up and the temperature gets a lot warmer on Mars, and you might get that ice sublimating and turning into gas, but it would almost be lost from the atmosphere faster than it could build up the pressures required to make it habitable. 

Pamela Gay [00:28:17] Yeah, exactly. It takes a long time for the gas to go away. The Martian seasons actually allow the ice caps to partially melt and become a thicker atmosphere. And then they refreeze in the winter. And so we do have this cyclic freezing and melting of mostly carbon dioxide, but we can’t make the atmosphere thick enough that water can flow on the surface. What we can do is build really big domes, and that could just be fun. 

Speaker 3 [00:28:50] Right. 

Pamela Gay [00:28:51] And if you have a really big dome and you have a warmer sun, then you’re down to just trying to figure out what to do about radiation. Which is a challenge, nonetheless. 

Fraser Cain [00:29:02] Yeah. 

Pamela Gay [00:29:03] But that’s a technological challenge. All right. 

Fraser Cain [00:29:07] And so next week we will talk about some of the missions that have gone to Mars and some that are coming up in the next couple of years. And then as Pamela said, the third part of this is we’re going to actually talk about the plans to send people back to Mars and what the far future might hold for that. So we’ll talk to you next week. Have a good time at the meeting. 

Pamela Gay [00:29:32] And I just might see some of you tomorrow. That would be great. 

Speaker 3 [00:29:35] So thanks a lot, Fraser. 

Pamela Gay [00:29:37] All right. 

Speaker 3 [00:29:37] It’s a pleasure as always. 

Pamela Gay [00:29:38] We’ll talk to you next week. 

Speaker 3 [00:29:39] Bye -bye. This has been Astronomy Cast, a weekly facts -based journey through the cosmos. Show notes and transcripts for every episode are available on our website. Check it out at astronomycast .com. You can send us any comments, questions, or feedback to info at astronomycast .com. We read every email. This show is a nonprofit educational resource provided by Fraser Cain and Dr. Pamela Gay. We’re supported through the kind donations of listeners like you. If you enjoy Astronomy Cast, why not give us a donation? It helps us pay for bandwidth, transcripts, and show notes. Just click the donate link on the website. All donations are tax deductible for U .S. taxpayers. You can support the show for free, too. Write a review or recommend it to your friends. Every little bit helps. Click support the show on our website to see some suggestions. To subscribe to the show, point your podcasting software at astronomycast .com slash podcast dot xml or subscribe directly from iTunes. Music is provided by Travis Searle. The show was edited by Preston Gibson. Astronomy Cast is produced at Southern Illinois University Edwardsville with generous support from Universe Today.