 Greetings and welcome to the Introduction to Astronomy. In this lecture we are going to talk about the planet Mars and more specifically its geology and atmosphere. Now, Mars is one of the primary planets that we look at for a possibility of having life and that's because it is the only planet other than Earth that has been known to have liquid water on its surface in the past. The conditions on Mars no longer allow liquid water but because that possibility existed in the past it gives us the hope perhaps that we are able someday will be able to find some kind of either life or fossilized remnants of Martian life that might have existed at one time. So let's start off looking at some of the exploration of Mars. Mars has been probably the best explored planet with probably two dozen craft that have visited it over the last 50 years or so. So we can go back to some of the earliest ones which would be the Mariner spacecraft. Mariner 4 in 1965 was the first successful Mars flyby. So it flew by Mars giving us our closest images of it to date. Mariner 9 six years later in 1971 was the first spacecraft to orbit another planet. So the first time we had actually orbited another planet in the solar system. Now a little later in the 1970s we had the Viking craft. The Viking 1 craft was a good lander on Mars and the first successful landing on Mars. And you can see it here. This is part of one of the feet of the craft as it landed and you can see some of the Martian rocks there close to where it landed. And that was a chance to be able to explore and look for life. The Viking lander drilled into Mars looking for samples and trying to test those samples for any signs of life. Now more recently we have the Curiosity rover which has been on Mars since 2012 and is currently exploring Mars today. So here we can see an image taken of it by itself, actually a number of different images, then stitched together to show us an image of the rover itself there on Mars. And it explores the entire part of the surface of Mars within the crater that it was landed on. So that is one way to be able to explore. And the rovers in a way are better than things like the Viking craft which landed but could not move. The Curiosity rover can move around and travel to explore slightly different areas. So if something interesting would be just out of reach for Viking, it's possible to direct the Curiosity rover there to be able to explore it. Now what kind of samples of Mars can we explore? Well we actually do have some samples of Mars here on Earth. Certainly the landers and the rovers have been able to study samples on Mars, but we have not yet had any samples returned to Earth. So we have not yet sent a craft that went to Mars, picked up samples, and brought them back from Earth here to Earth to study in the laboratory. However, we do have meteorites from Mars. So there are meteorites that we have detected here on Earth that show features that relate to them being from Mars. Now how can we get a piece of Mars here? Well, as with all other objects, there have been large impacts on all of the other planets. Not just here on Earth or just on the moon, but we have seen those on Mars as well. And in a very large, a massive impact, material could be thrown off with the escape velocity of Mars, meaning that it can then escape from Mars and head off into space. And some of those would eventually make their way here to Earth. Interestingly, we find that these are relatively young, only 1.3 billion years old. So they are relatively young, so something that would have had to have happened in the more recent past, not dating back to the very early history of the solar system four billion years ago, but only 1.3 billion years old. But those are samples of Mars that we could actually study here on Earth. Now let's look a little more detail at Mars and some of its surface features. So what do we see? Well, here is a nice image of Mars that we can see. We see some of the major features. We do see some craters. Not so much in this image. You can see a few scattered around. There are some cratering that does occur. So Mars is kind of intermediate between everything else. It has far more craters in the Earth than Venus, but far fewer than Mercury and the Moon, putting its age in between those two. So Mercury and the Moon would be the two oldest objects. Venus and Earth would be the two youngest. And Mars would be in between. We do see volcanoes on Mars, and you can see several of those off to the side here. There are three of them in this case, and there's another even larger one that we'll look at in a minute that's off kind of off the edge of this image. These are massive volcanoes compared to anything that we have on Earth. And again, I'll look at those in a little bit more detail, but they are incredibly massive volcanoes. One of the reasons for that is that Mars does not have plate activity, and therefore the volcanoes keep occurring in the same spot over and over again. So unlike the Hawaiian region on Earth, the Hawaiian islands, where the chain of islands is formed because the plate is moving, here on Mars the plate didn't move, and the volcano erupted in the same place. We also see great canyons, not like canyons on the Earth, but great tectonic features. And we can see what is called ballas marineris here. And that is a gigantic tectonic feature that has since been eroded away. This would stretch across the entire United States. So it's a gigantic one. You could put Washington DC on one side, and the other side would be out towards San Francisco. That is how large this tectonic feature is. So it is more like some of the great rift valleys that we see here on Earth than things like the Grand Canyon, which would be negligible compared to this size. We also see flowing water features on Mars. Not current, but enough to know that water has flowed on Mars in the past. So let's look at some of these in a little bit more detail. First of all, volcanoes. We have things like Olympus Mons. Olympus Mons is the largest volcano in the entire solar system. It is three times the height of Mount Everest. So were you to climb Mount Everest? That is the equivalent of getting one third of the way up Olympus Mons. We can see it here, how it stretches out. The peak here is the caldera. That's where lava would have flowed out. And then lava would have flowed down the sides, again, over billions of years ago, and spread out on the surface. To get an idea of how big this is, let's compare it. It's about the size of France. So if we put the two here, there is Olympus Mons in the inset here. So this is just about the size of France, would cover most of France. And this little section here is the caldera where the material would have erupted from. So this is an incredibly big volcano. Now the whole region, actually, around it is volcanic. And we saw on a previous slide, we were able to see three of the volcanoes. And let's look at them here again. Here are those three volcanoes that I noted on the original map of Mars. And here is Olympus Mons. This entire region is called the Tharsis region. And that is a hotspot region on Mars, very similar to Hawaii here on the Earth. However, the chain is not because of plate motions. It's because of just three separate hotspots. So one hotspot here and one for each of these volcanoes. And then they would have continually erupted in the same spot over and over again. Because of massive pressures underneath us, actually this entire region is pushed up by seven kilometers. So not only are there the high mountains, but this entire region here on Mars, as noted here, has been pushed up much higher above the regular surface level of Mars. Now Mars is not all volcanic. We have other features as well. Let's take a look at Valles Marineris. So let's take a look at Valles Marineris here. It is a very long canyon, 4,000 kilometers long, much, much larger than the Grand Canyon here on Earth. So as I said, this would stretch across the entire United States. You can imagine some of these little side canyons would be similar in size to the Grand Canyon here on Earth. It is formed by a different process. The Grand Canyon on Earth is formed by running water. So water in the river that has eaten away at the ground and caused it to erode away. Here, this is actually a tectonic feature that has crack, essentially a big crack in the crust that where the crust was separating. So very similar to a rift valley here on Earth where the plates, maybe plates, that were starting to form were actually separating. However, Mars was much smaller and cooled off too fast for all the plates to form. And so this region is kind of locked in place. Now, one thing we note is that the Tharsis region is to the left of this image. So that would be over on this side. So could that be the cause of this rift? Is the volcanic region there part of the reason that the rift happened to form at this specific point? But Valles Marineris, again, one of these very large features that we see on Mars. Now, Mars does have an atmosphere as well. So we can take a look at that here. It is an extremely thin atmosphere, less than 1% of the Earth's. So we can see it a little bit in the image here off at the edge where it's a little bit hazy. That is looking through with the atmosphere. But it is very thin. So even if it had the same composition as the Earth, you would then be unable to breathe because the pressure would just be too low. However, its composition is also nothing like the Earth. It is 95% carbon dioxide. It is 3% nitrogen and 2% argon. So no sign of things like water, no sign of things like oxygen in the atmosphere. The thin atmosphere does have some very high winds and dust storms, where high winds will pick up dust from the surface that result in dust storms that engulf the entire planet. So they don't just cover part of Mars, as a large dust storm might cover part of the Earth. However, they can cover the entire planet. So very extreme dust storms that occur here on Mars. But it's a very, very thin atmosphere, thick enough to have to worry about if you're landing, if you're trying to go through it, where it would cause friction, but not thick enough to begin to be able to breathe. So the last thing we want to look at at Mars here are the moons of Mars. We didn't have any moons to talk about with Mercury or Venus because they don't have any. However, Mars does have two small moons. We have Phobos, which is the doomed moon. And we see that one here on the left. And we see Deimos, which is the other moon of Mars here on the right. Phobos is only about 6,000 kilometers from the surface. That's very close to the surface of Mars, actually so close that it orbits faster than Mars rotates. So that means that it moves faster. That means it's moving through the sky and will end up rising in the west and setting in the east because it is moving faster than Mars is rotating. And its motion dominates its rising and setting. It is being torn apart by tidal forces. So when will it be gone? Well, you can see some of the stresses here, these lines that occur, are actually some of the stresses that are beginning to slowly pull it apart. That doesn't mean it will be gone tomorrow or next year or even in a decade, but in millions or tens of millions of years, likely it will have been ripped apart and probably crashed into the surface of Mars. And then Mars will be down to just one moon. Deimos is the smaller of the two. And we can see on both of these we do see impact craters. So they have been hit by smaller objects as well. We don't believe that they form through a giant impact like the Earth's moon. We feel more likely that these have been captured. These are asteroids that have been captured by Mars. Likely Mars being so close to our asteroid belt had lots of asteroids pass near it. And these too happened to pass just right to be able to be captured. So let's finish up with our summary as to what we've covered on Mars here. First of all, a large number of spacecraft have visited Mars and more are planned. So lots of exploration of Mars coming up. We do see large volcanoes and large canyons on the surface of Mars, so very large features compared to what we see on the Earth, especially for such a small planet. The atmosphere of Mars is very thin and is primarily carbon dioxide, much like Venus's atmosphere. And we did note that Mars has two small moons, which perhaps are asteroids that Mars captured in the past. So that concludes our lecture on the geology and the atmosphere of Mars. We'll be back again next time for another topic in astronomy. So until then, have a great day, everyone, and I will see you in class.