 Greetings and welcome to the Introduction to Astronomy. In this lecture we are going to continue talking about Mars, this time specifically looking at water on Mars, and the possibility of life. So what we know is that Mars is one planet in the solar system that currently has water on its surface. Now it's not liquid water, but the polar caps, there are several of them, there is a permanent polar cap which is ordinary water ice. And then there is one that changes and comes and goes with the seasons and that is carbon dioxide ice or dry ice. So we do know for sure that Mars had water, has water on it right now, but it does not have liquid water. Now there's also a permafrost below the soil, so when we look down below the Martian soil here dug up by one of the rovers and here we see it four days apart, four Martian days apart at least, and a Martian day is about a half an hour longer than an Earth day. And you can kind of see the changes in the inset images as to material that has been vaporized and sublimated out into the atmosphere. So material that is down below and below there is a good layer of permafrost down below the surface. We know that there is no liquid water on Mars right now, certainly nothing like anything we have here on Earth. Why? The atmospheric pressure is too low and that means it undergoes sublimation, so it goes from a solid directly to a gas. You might be familiar with that with the dry ice or carbon dioxide ice here on Earth. Well on Mars, based on those temperatures and pressures, water will do exactly the same thing. So it will go from a solid to a gas and back, but it will never go through a liquid stage. Now how about how about flowing water on Mars? Well there is evidence from flowing water in the past, we can see evidence of things like dried riverbeds. And what this tells us is that water must have been thicker in the past. So we see some areas like this where you can see very distinct features that are water related. However, we also note that they are heavily cratered, meaning that these flows are very definitely not recent. So how about flooding? What other signs of water do we have? Well we have things like this where we can see signs of water flow around the craters. So around this region you can see around some of these craters where water had flowed. So around this one you can see the material built up so the crater itself kind of diverted a water flow around it. And you can see various features as we would associate with the flash flood here on Earth so that there has been flooding on Mars in the past. What other evidence do we have for water? Well we have sedimentary rocks that have been found by some of the rovers. Well sedimentary rocks are layered rocks that can only form in liquid water. So again the fact that we see these and we see them no place else in the solar system other than Earth and Mars. Notice that at one point Mars did have an ancient lakes and or oceans. Certainly not as big as Earth's oceans, at least not in depth, but it may have covered a large portions of Mars' surface to a depth of even a couple of meters. So while maybe not oceans like we have here, still Mars may have been a very watery world in the past and in fact it was because we find all sorts of evidence of water. Another thing that we see is a mineral called hematite in the rocks. And those are that forms in liquid water as well. So all of these things put together tells us that yes Mars has had liquid water in the past. But what has happened to that and what's going on today? Is there any liquid water left today? Well I've already told you there really can't be any liquid water as we see here on Earth. However we do note craters like this one with dark streaks down the side which could be caused by flowing water. However it is not water as we know it. It would be a very thick briny water that would flow down and would flow down only part way before it quickly evaporates just leaving the streaks of the salty material behind. So could there be flowing water on Mars? Yes but it would not be anything like water we would recognize here on Earth. So we do know that water has existed on Mars in the past and that kind of leads us could there be some kind of life on Mars? Well what is this? What is the possibility of life on Mars? People have often looked at this as the face on Mars and if we look at the leftmost image you might see yeah it looks like there is a face there. Well that's actually an optical illusion because if we look at the same region in higher resolution with later later craft we see that there really is no face there. It just is a randomness of the pattern that gives us the idea that you know our mind is trying to make sense of that randomness so it tries to put the closest pattern it can find and since we may see a couple of eyes and a nose and a mouth there it may give people the impression of a face and then once one person sees it then again other people can will start to see the same thing. You can also look and search for similar images of the rat or the iguana on Mars which are exactly the same type of thing but to be clear these are not signs of life there has never been an advanced civilization on Mars. If there had been we would have known about that by now we would have been able to detect the remnants of that civilization. However that does not mean there is not life on Mars what about simple life? Well this is possible we did have liquid water in the past however the surface right now is sterilized by ultraviolet radiation from the Sun. On our earth the ultraviolet radiation is blocked out by the ozone. Well Mars does not have any ozone layer so it is constantly bombarded by ultraviolet radiation which sterilizes the surface. However it doesn't take much to be able to protect the layers down below a thin layer of dirt is very good at absorbing all that ultraviolet light and therefore anything below the surface is shielded. So when we look for life we don't look for life on the surface we dig below and here we see the Viking craft as they dug some samples to test some samples and look for signs of respiration and absorption of nutrients kind of saying that there might be life there. What were the results? Well neither negative or inconclusive nothing that we could say for sure was a sign of life. So how about fossilized life? Again we're looking for very simple creatures we're not going to find fossilized animals or complex plants or any other kind of creatures there like that. However we might be able to find some signs of any kind of very small fossilized microbial creatures. And the question comes up why Mars? Why do we look at Mars when we're talking about life? Well the conditions on the in the distant past were similar to what we have on earth so we know that liquid water once existed on the surface. So it makes Mars really the most earth-like planet in terms of looking for life. Later on we'll look at other objects and we'll consider some of the moons in the outer solar system as other possibilities for life. But here really Mars is probably the best bet right now to be able to find if there is currently any kind of simple life or even if there was some in the past. Future experiments are planned to bring samples back to earth for a more detailed study and of course who knows what might be found. So let's go ahead and finish up with our summary and what we've looked at today on Mars is that we do have water on Mars today in a solid form so ice. There is significant evidence that liquid water also existed in the past so we know that water has been present on Mars. However experiments testing for life on Mars have either been negative or inconclusive. So we can't completely rule out life on Mars but we certainly cannot say that there is or has been any life on Mars at this point and the experiment and sample taking and testing continues. So that concludes this lecture on Mars, water and life. 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.