 Greetings and welcome to the Introduction to Astronomy. In this lecture we are going to talk about Mars and focus on water and the possibility of life on Mars. Mars being the planet that in many ways is most like Earth, having had liquid water in the past, is the one that we look at most to possibly have had some kind of life. So let's take a look at that today. First of all, what do we know for water on Mars? Well, water on Mars does exist today. But when we say water, that does not necessarily mean liquid water. We know that there is water in the polar caps, and in fact the permanent polar cap is made of water ice. When we watch the polar caps on Mars, they will grow and shrink with the seasons. That is not the water ice that is changing. The water ice remains frozen. At the temperatures and pressures on Mars today, the water ice cannot change. But the carbon dioxide ice, or what we call on Earth, dry ice can change. So that can actually cause the polar caps to grow and shrink, and it's seeing the change in the carbon dioxide ice. We do see some permafrost below the Martian soil. So if we look down below Mars, we can actually see that. Now, how do we look below the soil? Well, here we can see a little bit of one of the rovers where we were able to dig into the soil. So use the rovers to be able to dig into that. You can see the reddish Martian soil here. And you can see some signs of materials that are very much related to water, and that did not last a very long time. So you can see here, you can see all of the wider areas present, and that just for Martian days later, going from 20 day 20 to day 24, that they were gone. So a lot of those areas were then wiped out, as that material was then exposed to the intensity of solar radiation. So we do know that there is some water between the permafrost below and polar caps on the poles of Mars. However, there is no liquid water or not any significant liquid water, primarily because the atmospheric pressure is far too low. That means that liquid water on Mars would behave like dry ice does on Earth. It would undergo a process called sublimation. And if you had a solid water, a block of ice say on Mars, and it got warm enough, it would not melt as it does here on Earth. It would change directly from a solid into a gas. We see that with dry ice here on Earth, at the temperatures on pressures on Mars, liquid water would do the same thing. So is there flowing water on Mars, or has there been? And we do see some evidence of that. We do see evidence of things like dried river beds, and we can see some of that here. So are there dried river beds? And if you look here, you can see some areas, perhaps, that look like various tributaries and channels that have been present on Mars so that water'd flowed in the past. Now we know that that was a long time ago just looking at the number of craters that we see around it. So it's been heavily cratered since then. That means a couple of things. That means, first of all, the atmosphere must have been thicker in the past, because under current conditions, you could not have flowing water like that on Mars. You must have had a thicker atmosphere to give you the higher pressures and temperatures that would be needed to allow water to flow on the surface. Again, we also see that it's a heavily cratered region so that the flows are not recent. It has been a long time since we have seen liquid water on Mars. We also see evidence of flooding. You can take a look at some of that here. And what do we see for flooding? Well, there are some areas here. You can see where it looks like something has flowed in the past, and you can see the channels that it has made around various objects. Higher-level objects remain. Here, for example, a crater where it looks like material has been eroded around it, but the crater itself actually protected the materials or materials. And, of course, again, see up here, we can see some various flows and some higher-level areas that remained up above them, so it looks a lot like flash floods that you would get here on Earth. We, again, know that it's not brand new recent, although maybe more recent than the other image, because we still do see a number of craters present in the image. Now, some of the other evidence that we see for water would be things like sedimentary rocks. Sedimentary rocks occur on the Earth from water flows, so water in liquid water, they require that, and they are layered rocks. We did not see any when we talked about the Moon. We didn't mention any when we talked about Mars, sorry, Mercury. We didn't mention any in Venus, but we do have some here on Mars. So it is the only place other than the Earth where we have found sedimentary rocks. We have also seen evidence of lakes and oceans that possibly existed in the past. So we've seen that. We've seen some hematite in rocks, which forms only in liquid water, and we see evidence of evaporation. So all these little bits and pieces we can put together, and we can say with very good confidence that liquid water did flow on Mars in the past, that there was liquid water, and that leads us to the idea that there could have been life at some point in the past. The question is, is there any liquid water on Mars today? And the quick answer is really no, but there is some possibilities that have been studied recently where we see, for example, the dark streaks in this crater which were possibly caused by flowing water, and these formed very recently, just within a very short time frame, as material was being heated up. So relatively recent, within a year or so, but however, this is not water as we know it. It is a very, very salty, briny water that would briefly flow down, the crater could flow down the crater walls, leaving, it evaporates very quickly, leaving the salty material behind as deposits as it flows. But it is a sign that we have seen very recently that liquid water of some type at least still flows on Mars today. However, nothing like the rivers or the floods that we saw in the previous images. Now, the big question, of course, is, is there life on Mars? So let's look at one example here of something that often comes up which is the face on Mars, and you see that here on the left, and it looks like there is a face that is in part of Mars here, where you can see a mouth and a couple of eyes of some kind of creature on the surface of Mars. However, this is really just an optical illusion. As we can see in a higher resolution photograph, we lose all that structure that was visible. When we have a low resolution or not a lot of detail, our mind will try to make sense out of things that are really just random patterns. And if you've looked around the Internet, you can actually find similar images that are supposed to be a rat or an iguana on Mars. Again, it is the same thing. If you can look at them in high enough resolution, there's nothing there. But at a very low resolution, your mind does try to play tricks, and especially when you say that, hey, there's a face there, people start to see it because your mind does not like randomness, so it tries to put some kind of order to it. Basically, any of these are not signs of life. Very definitely. There has never been an advanced civilization on Mars. We would know that. We would be able to detect the remnants with everything we've studied and images we've been able to take and exploring with the rovers. We would know if there was any kind of advanced civilization. However, that does not rule out necessarily all kinds of life. And what could be present on Mars or could have been present of simple life? Now, that is possible since liquid water once existed on Mars, but not really on the surface anymore. Mars has a very thin atmosphere, no ozone layer, so that means that it is being bombarded by ultraviolet radiation from the sun and essentially being sterilized. So the surface is sterilized, so one of the things that the landers and rovers do is to actually dig down below the surface here. You can see some of the places where it's dug, to look for signs of life. And what the Viking lander did was to be able to look for signs of respiration and absorption of nutrients. So essentially we picked up a sample of soil and looked for any evidence of gases coming out or nutrients being absorbed, nutrients that were added to it being absorbed. And really results were either negative or inconclusive. So there were some cases where you could have, you might have had some signs that could have been gases being released, for example, but not necessarily that was life. It still could have been a chemical reaction. So everything was negative or inconclusive at this point. Could we look for fossil life? Could we look for fossilization? And could there be some very basic things similar to what was present on the Earth three and a half billion years ago? And that is something else that can be considered. So why do we concentrate on Mars? Well, there are some features of Mars that are very important, and one is that the conditions were similar to those on the Earth, in the distant past. We do know that liquid water once existed on the surface. So future experiments planned are to bring samples back to Earth for a more detailed study. It's a lot easier to study things in the laboratory here on Earth than it is to just be able to see them elsewhere. And who knows what might end up being found in this? So let's finish up with our summary here. And what we have is we do know that water does exist on Mars today. It is not in a liquid form, but in a solid form of ice, either in the polar caps or in the permafrost. We do know that there is significant evidence for liquid water that existed in the past. And we've done a number of experiments looking for life on Mars. To date, they've all been either negative or inconclusive. So no evidence that life does exist on Mars, but studies will continue to try to find better experiments and to be able to get better knowledge of that. So that concludes our lecture on water and life on 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.