The Mariner 8 spacecraft was launched towards Mars in 1971. Scientists were quite excited. There were a pair of spacecraft going; Mariner 8 and 9. They were going to map the entire planet. They were going to look at variability across different regions. Mariner 8 went up, didn't achieve orbit, went back down into the Atlantic Ocean. Mariner 9 launched, achieved orbit, made it out of orbit, headed towards Mars, got to Mars and successfully went in orbit around Mars. It was the first time that any spacecraft had been made to orbit around another planet. And as soon as it got there or even as it was getting there it started getting the best images of Mars that had ever been seen. And what did it see? Well, it saw a dust storm. Mars was enshrouded in one of its periodic huge dust storms and it obscured almost the entire planet. Images looked kind of like this. The dark spots that you see were just the marks inside the camera to get the scale right. This dark line that you see moving up here like this is really just a data processing artifact. And so the fact that nightside is over here. And the features that you see on here, well, there aren't any. It was really quite a disappointment to get there and see almost nothing but not entirely nothing. Here's another image and if you look really carefully you see that it's not completely bland. There's something going on. Where is this something? Well, this is still that same dark band exactly same as before. But there's a spot right there. A spot. Must have been pretty exciting to finally see a spot. Not only that it's a spot that could be identified with a known region. We knew even though the planet was enclosed in dust at this point, we knew what was supposed to be underneath the cameras at any point in time. And this was a spot that had been seen from the ground before, and at the time it was called Nix Olympica. Nix means snow or bright. Nobody knew what it was. It as just a bright spot, Olympica. And so it had gotten one of those names, Olympica, is one of those original names that was given to it in the very earliest mappings. And what's interesting is it's visible even with all of the dust around. We'll get to why in just a minute. But in the meantime, the spacecraft sat there for months. They didn't know how long the dust was going to be there although global dust storms had been observed on Mars before and so they knew that it was a potential to have to wait weeks to months before everything cleared up. And so in the meantime the spacecraft was retargeted to go fly by the moons of Mars and these were the first close up images of the moons of Mars. But over the months over about three months, the dust started to fade away and features started to emerge out of that dust. The first ones that started to emerge were associated with this region like Nix Olympica. In fact, here's a beautiful image of a surface almost entirely covered in dust. You don't see very much of anything all throughout here, all throughout here. But what do you see? You see these three round things. Why would these three round things be visible when nothing else is visible? There is only one good reason and that's because they are elevated. They are not only on a large elevated province, this region in general is called the Tharsis region. The Tharsis region is elevated, we now know, elevated above much of the rest of Mars. And these are three giant mountains on top of Tharsis. Very interesting. Let's take a close up look at one of these giant mountains. And if you look very carefully here, you'll see that there's something going on at the summit of each of them. But there's something going on, looks a lot like a crater, centered on the top of those mountains. Let's take a look. Here's the very top of what we now call Olympus Mons, the Mons for mountains, the Olympus from that Olympica that it used to be called. And look what we see. Well, we see not just craters but we see craters within craters. We see a big crater maybe like this, we see another crater that looks like it's below the level of this one, we see another one that's here. We see potential for multiple layers of craters in through here. What could cause something like that? And most importantly, you don't see craters over here. You don't see craters in almost any of the other regions. There's maybe a little crater there, a couple of small things here and there. The fact that we have multiple craters in one region that's otherwise generally smooth, is a big clue to what's going on. And how do we figure out what's going on? Well, in this case we use the general idea of terrestrial analogies. We look for regions on the earth that we understand that look the same and we make the case that it's a similar process happening on Mars at this point. Where is a place on the earth that looks the same? Well, this looks a lot like the summits of terrestrial volcanoes. The summits of terrestrial volcanoes often have a region at the top called a caldera and the caldera is a collapsed crater. That collapsed crater comes because there was a magma chamber underneath as the volcano was active or in previous phase of activity and that magma chamber empties in some eruption and then collapses down. When it collapses down the top of this mountain collapses down with it and you get a crater on the top. Then you can also have little miniature smaller collapses, maybe another smaller magma chamber get another collapse in here or collapses on the side. Let me show you a terrestrial example of what one of these looks like. This is a Google Earth image of the caldera on Kīlauea. Kīlauea is an active Caldera on the big island of Hawaii. And I show this one because it's the only active volcano I've ever actually seen in real life. I have walked all the way around through here and in through here, not when it was steaming quite like this. And it's a beautiful location; it's actually close to the telescopes I use on the big island of Hawaii. The telescopes of course are on top of another volcanic peak. But in any case, what do you see? If you can very carefully make out this is the edge of the main Caldera around here. There it is. You can see the edge down here really well. I'm outlining that, there's a nice hotel The Volcano House Hotel, you can stay at. The edge of that cold air goes right to here. There's another smaller Caldera that has collapsed inside of it. There's another Caldera, this is where all the steam is coming from. There's another caldera inside there. And in fact if you were to go to this Volcanoes National Park right now, you're not even allowed to go on this section because this has become not just a caldera but there's actually a lava lake inside here, which they don't let you to get up close in seeing; which is just devastating to me because I would love to see a real lava lake. But this looks a lot like that picture of the top of Olympus Mons that we saw before. It had craters, craters within craters, craters to the sides of craters. These are the sorts of analogies, in addition to the fact that Olympus Mons is at the top of the mountain. These are the sorts of analogies that make you pretty clear in this case that you are looking at the summit of a at least once active volcano. And in fact you're not looking at the summit of any once active volcano, you're looking at the largest volcano anywhere in the solar system, the largest mountain anywhere in the solar system. We'll talk later on why this volcano, Olympus Mons on Mars, got to be so big. One of the fun things you can do these days that you couldn't do in 1971/1972 when these images actually came down, is that you can go try to find this location on not Google Earth like we just looked at Kīlauea, but you can look at Google Mars. How do you get to Google Mars? Well, Google Mars you first start with Google Earth, which you can download for free, and then you go up there, a lot of ways to get there. I just go to "View" and I go to "Explore Mars". What do we do? Well, we go explore Mars. Here we go. Now what you have on Google Mars is a kind of a hodgepodge of different images from different spacecrafts. Sometimes you can get very high resolution, sometimes you can't get particularly high resolution in different places. But it's a fascinating tool to go wander around and explore what's going on on Mars. Let's find what this image is of, which is Olympus Mons, and let's see where we go. There it is. And Google Mars is a little bit crazy and goes in a ridiculous resolution. But let's zoom back out again and see if we can find what this view is that we were just looking at. Olympus Mons up, there is the beginning of the crater. There is something like what we might have been seeing. In fact, I think that if you turn it around to just about here and you look at it a little obliquely maybe like that, then you see something like the same view that we were just looking at. And in fact, see this crater right here, Pangboche, I don't know who named that. I don't see it over here and maybe that's because it's actually below the level of the dust storms. I love this image of the top of the caldera of Olympus Mons because now you can really see what a spectacular volcanic caldera it is. You see these sharp walls where it's collapsed down. There's another layer inside of here. You can see another collapsed crater here and all sort of stretch marks and collapse marks. It is just absolutely spectacular. If all Mariner 9 discovered were these gigantic volcanoes on Mars that would be a pretty spectacular mission. But it did much, much better than that. As the dust began to settle, more and more features were able to be seen on the planet. One of my favorite images from that sort of middle dusty period is this, which is, well, what is it? It's huge. This is the limb of Mars over here. And so this is a feature that covers a pretty significant chunk of the distance across Mars. These days we know it's the gigantic Valles Marineris, named after Mariner. The Mariner mission which is the one that discovered this gigantic canyon system on Mars got the honor of having the name of that canyon after it. Valles Marineris is the biggest Canyon anywhere in the solar system, we'll talk a lot more about it later. And it must have been amazing, day after day watching the dust slowly disappear out of the Martian atmosphere and trying to figure out what the heck this thing was that was slowly emerging out there. At least as spectacular though were images like this. This is a region called Nirgal Vallis Valley. It's obviously a valley and suddenly Mars doesn't look like a dry dead place like it did in the earlier missions. What is this? This looks to all the world like some sort of river valley or some sort of something; some sort of network of flowing going down. You can look at it, figure out which direction it's going. Clearly it must start here. These branches come into the main branch, it gets bigger, it gets bigger. And I encourage you to go look up Nirgal Vallis on Google Mars and you can see the entire valley network. And it's pretty spectacular as it gets down through here fewer branches come in and it's a nice big sinuous valley going. And up in here, there's some finer branches. What is it again? How do you figure out what something like this is on Mars? You can't go there and go figure out what has been carving this river. But you can start to use terrestrial analogies again. And geologists, when looking at this, immediately jumped to the analogies that they know best, in arid locations where you have these boxy looking heads of canyons, you don't have what we think of as a regular river valley. Regular river valley, let's say formed by rain or snow or something, you have drainages all over the place coming into these rivers. You don't have sudden starts like this and branches that are big fat and stubby. In fact a regular river valley looks more something like this. This is a view from the space shuttle looking down of the mountains in Tibet. And you can really see that every single spot has some sort of drainage. So when it rains, when it snows, that water gets down from every spot to get into the main river channels in all directions. This is called a dendritic river system. It does not look like this. What does look like this? This is an image of the Escalante Canyon in Utah, again taken from Google Earth and you see something that looks a lot like these channels on Mars. Look at this little region down in through here in particular, and you can see that each of these little branches is a stubby little branch with very little drainage anywhere else. Here's another nice set of examples. Of course there's very little drainage anywhere else because there's not much rainfall. This is Utah. It's a very desert-like area as you can even tell from the image. And none of these seem to have much in the way of feeder channels; maybe over here you can start to see something that looks like little streams coming and forming bigger streams, coming in but most of these big carved out regions really start from, it looks like, nowhere. In fact, let's see how much they look like they start from nowhere. I'm going to zoom in on this little region here and we're going to look at where some of these canyons up through here really start. If you look closely here you can see here is the rim of this canyon coming along in through here and it's incredibly steep. There is no feeder stream coming in here that's making this, no feeder stream coming in here. What's happening in these cases is what's called groundwater sapping. There are springs running underground and over time they loosened and weakened the rock over them and a little bit collapses. And then when that happens that canyon advances a little bit more and then it collapses again and collapses again. And so you have these things growing in this direction but always is a big collapsed section of the Canyon. I like this particular image because you can also see that in each of the places where the canyon is growing inward, it has the inward cave like this. There's green. The green in through here of course is because something is growing there. Why is there something growing there? Because there's water. This is the groundwater that's sapping in through here; the springs that are causing the collapse of this otherwise relatively flat region up through here. There's one more image of this sort of thing that I think is actually even more striking compared to Mars. This is a picture of a small region along the Apalachicola River in the Panhandle of Florida right here. I can say Apalachicola correctly because this is from where I grew up almost. I grew up right about here in Alabama, if you draw it like that, not right there in the Apalachicola. And I think that if you looked at this and you compared it to Mars, you would, like I would say, holy cow. Look at this. This looks like exactly the same thing. What's going on here in the Apalachicola? Well, there are underwater springs in through here. But here you're not in this desert dry region where it's sapping into that. These are salty flatlands and the salty flatlands decay away or erode away from the sapping so quickly that at the heads of these you can actually measure how fast they're going and much better than you can in the rocks in Utah. So these are great analogs for both the rocks in Utah. And again look at this, for what's going on on Mars, these things look really like the same stubby channels, no dendritic flowing in through them. And in this case you can really see exactly what's going on. You can see the underwater springs and you can see it going quickly. This is the way that what's called photogeology on a place like Mars works. You take these large scale pictures and try to compare them to something you know and try to learn something about Mars. What have we learned about Mars in this case? Well, we've learned not that there was water flowing on the surface, not that it was necessarily raining and water accumulating, but at least that there is water or was water in the ground and that that water sapped out flowed to-- well, we'll talk about where it flows to later. But it existed, and that at some point in time water was flowing not necessarily on the main surface here, but flowing out of these aquifers and flowing through these channels and digging these things out in the same way that these are dug out in places like Florida. We're going to keep looking at features like this and some of the other evidence for water flows that came from Mariner and then from subsequent missions too in the next couple of lectures.
