I'm not sure you need even more evidence to convince yourself that there's ice in the sub surface, even at low latitudes on Mars. And yet I'm going to give you even more evidence, because these lead to some pretty dramatic spectacular pictures. If you look at regions in Mars, maybe some of the higher elevation regions closer to the equator. You see these really interest features that, well let me show them to you and see if you can figure out what they might be. Here's a pretty spectacular one I think it looks like, maybe, a large piece of chocolate that was placed on the surface of Mars that started melting. Look at this region around through here. You can tell that something happened, that something either the, this, this mountain is melting and flowing off, or something was on this mountain and flowing off in this direction. Pretty spectacular looking. If you look even more carefully, probably can't see from this image here, but you can see a series of ridges going sort of like this. You can see them better up in here, but we don't have a very good view here. Here's a series of ridges. What does that look like? Well okay, melting chocolate, but let's, let's keep going. How about this one? Don't say melting chocolate. Yes, it looks a little bit like melting chocolate I should tell you that there are mountains over here on this side that things look like they're flowing down to in this way. This is a valley through here and look at that. Here are these Ridges that you see in through here. Series of ridges that are parallel to the edges that you have here. And then a series of big, sharper lines in through here. Flow features going in through here. Clearly, this is something that has flowed in the past. What is it? Let's look at one more. These are four different views of the same, whatever it is, here's the top-down view. You're looking straight down at this thing that looks like, maybe, a double crater. But something that looks like it's flowing out through here. This image A was created by taking a pair of images, like this image B, at slightly different angles And using the stereo vision to make a 3D map of it. In the stereo vision you can see that this, this region here, is higher than this region here, and you can see in particular in the blow up down here, that it's flowing down into this region here. And D is maybe my favorite part. As you look in at this tiny region in through here, looking at it magnified up in here, you can see these flow features compressed as it goes through this little constriction. And then you can see them come back out again through here. And again these ridges that are parallel to the edge. All these features, if you've stared at surfaces on the Earth long enough, should remind you of one thing. And that one thing Looks something like this on the Earth. This is a NASA view from space of the glacier. This is the Bering glacier in Alaska and we'll zoom in and look at some of the features that we're looking at but I, I just wanted to show you this overall view. We'll look at some of these flow features that you see in through here and we'll look at this little chunk. It's interesting We'll look at the ends of the glaciers over here, where they have these parallel ridges and we'll see how they sort of look like the things that we see on Mars. But first, let me remind you a little bit about how a glacier works. A glacier, like the type that you saw there, happens when you have enough snow That the ice and the snow doesn't melt over the course of the year, so it continues to build up, continues to build up, continues to build up, and compresses. Eventually, enough compression happens, and maybe with luck you'll have a downhill slope right here. Enough compression happens that the bottom of the layer starts to slide, water is created down here at the very bottom of the layer. By all the pressure and if there is a little but of a slope, the entire thing can slide. It continues to slide downhill like this until it ends. Why does it end? Well it's not ending because that's just how far the glacier is gone. It's this continuous process of snow happening here. Feeding the glacier here, and it's usually going down where it gets warmer and the evaporation it's getting stronger up here. So the glacier is disappearing until finally by the time it gets here, there is no glacier left. In the meantime though, a lot of interesting things happen. The glacier is So when it starts out here it becomes down this way and it pushes material down the hill and when it stops all those rocks, all that junk, stops with it. This is called the glacial moraine. Viewed from above, a glacial moraine would look like a big glacier filling a valley, perhaps. And at the end of that valley, they'll be a big pile of rocks. And if you ever been on one of these glacial valleys, you know exactly what I am talking about. You can see these piles. They might also be, piles of rock further on and further on. And that's because sometimes the glacier would have gone further in the past, if it was colder in the past because it would have taken longer for that material to evaporate. And, in fact, in almost every glacier around the Earth right now because the Earth is getting warmer, you can see these moraines extending out through here. Let's look more carefully at the NASA image of a, of the Bering Glacier. And in this view of the bottom of it, you can see these flow features. You can see what I really want to show you are these. These are the moraines. the, the rocks and debris that are left over from times when this glacier went further. You also have in this image these, these other things, these are the terminal marines, but these are lateral marines, side marines. As the glacier is moving along and pushing stuff off to the side. And you can see again the glacier used to be bigger and pushed up all the way out into here. Here is that upper corner of that picture of the Bering Glacier that I promised to to, show you. And I love this because you can see, like the the, dirt flow features that you see in up through here And every single one of them comes from the intersection of two glaciers coming in. This is, this is the high region of the glaciers. The glaciers are formed up in here, and they begin to flow down these valleys, through here. And notice, when this one, and this one meet, this, they're both pulling debris off the sides of the wall. And you see this dirt line that goes all the way down, as far as you can really see, all through here. Lets follow another dirt line. Look at this one. This one's a pretty dramatic one. Where does it come from? Well, it comes from right here. The intersection of these two glaciers coming in through here. And you can see intersections of even small things, like here, here's one that you can see. Here's another one that you can see where it comes from. When you look down here near the end of one of these glaciers, you can really read off the history of what this flow looked like. Is that what's really going on in Mars? I think we could look back again at these pictures and recognize things that look very glacial-like. This looks like moraine that's at the end here. These look like the same sort of flow features from the side. Maybe they're coming in from here, coming in from here, coming in from up here, you can kind of see that, is that really glacier? It's not really a glacier, because there's no ice on the surface. Does that mean that it's a glacier covered by dust? It must be covered by dust, because it wouldn't be standing. But if you covered a glacier with dust, this might be what it looks like. >> Is that what it really is? >> Well, we'll use our favorite phrase. Maybe. Just looking at it, I don't think you could say for sure. You could say, boy, it sure looks like a lot of these features look like they're glaciers. A lot of them are pretty low latitudes. How would we know for sure? The answer is, as is often the case with Mars, send another spacecraft with another instrument. This one had an instrument called SHARAD, which is an acronym, did I tell you that acronyms are always lame? Shallow radar. That's pretty a, pretty, pretty lame acronym. Shallow radar. Shallow radar was, remember how we talked about the laser altimeter We shot a laser beam down and came back up the shallow radar, instead of sending laser light, sends radio waves. The nice things about radio waves is they, of course, bounce off the surfaces here. But they will penetrate a light layer of dust and if this is just a light layer of dust and there is ice underneath there They'll penetrate pretty well through the ice also, and then bounce off the bottom if there is a bottom. Originally the, the one of the big motivations for this instrument was to look at the polar caps. And uh,you can really see some spectacular data if you look for Sharad data on the polar caps. And I want to show you one where a stripe was taken as the SHARAD instrument was gone across a field. There's a mountain in one location, a mountain in another location, and things that looked like glaciers on the sides of those mountains. And let's see what it looks like in SHARAD. Okay here it is. Imagine what happens the spacecraft sends down this radio beam, radio gets reflected back up, and the timing is one of the things that gives you a lot of information. Course, the problem is that this radio beam comes down and it can reflect off, of a lot of different places. There can be reflections from different things. And so it's a little bit confusing. It's not quite as simple as just that laser alternative and so know taking the known topology from the laser antibiter you can predict what you should get. So even on a very smooth surface with no weird subsurface features You don't get a perfect reflection just off of the, the top. When there are mountains, you get these strange little extra spikes going down. You get some weird stuff like that. And so, these, these simulations show exactly what you should see if it looked exactly like the top of it looked. And here is what Sherrod saw. Notice that here, it see's the top just like it's supposed to. And, there is another reflection down here. It continues down here I don't know what's happening right there. And look at this. Here's the next mountain. It sees the top just like it was supposed to, and another reflection on the bottom. And here is the best one. You see the top, like you're supposed to, and another reflection on the bottom. You don't just see another reflection on the bottom which is, interesting and weird. But notice that these are sort of flat. This is how if this mound were caused by a glacier. This is exactly what you would expect to see. This is pretty definitive evidence that, yes indeed, there are currently large amounts of buried ice not that far under a dusty surface covering. And this ice is, is extensive throughout Mars. Much more so than where ice is currently stable at the poles. Where did it come from? We'll explore that in the next lecture.
