Is There Liquid Water on Mars?
This month on Naked Astronomy, we're mulling over Mars. We'll be chatting about the question of liquid water on the surface of Mars. Is it there at all? And if it is, how do we find it? And to do that, Ben McAllister and Adam Murphy were joined by Lujendra Ojha from Rutgers University to chat about why Mars fascinates us...
Adam - Humanity has known about Mars since the ancient times, the Sumerians associated it with their death god Nergal, and because it looks red when you see it and it's connected with blood, the Romans named it after their war god, Mars, that is also where we get March from, the month of Mars.
Ben - I guess it's kind of hard to miss a glowing, bright red dot moving around in the sky. And certainly ancient astronomers knew all about it. Aristotle noticed that it would disappear periodically behind the Moon, which led to the conclusion that it must be further away than the Moon. So people have been noticing it for a while and trying to figure out more about it. I suppose it captured imaginations even all that long ago. Brahe and Kepler used parallax measurements to try and estimate the distance of Mars from our own home planet. And later in the 1870s, Italian astronomer Giovanni Schiaparelli went a step further, and claimed with his telescope that he could observe very strange and interesting structures on Mars that looked like canals made by some kind of intelligent civilization. Now, these observations were later debunked as telescopes got more and more advanced, but as you can see, people have been seeing Mars, trying to learn more about it, and making observations of it for a very, very long time.
Adam - And speaking of those observations, what kind of things do we know about Mars? Well, we know that it is the very next planet out from us, away from the Sun. And in comparison to the Earth, it's only about one 10th the mass and one 10th the volume of the planet. So it's our little neighbour.
Ben - So Mercury, Venus, Earth, Mars. Those nursery rhymes do ring true. Interestingly enough, one day on Mars, the amount of time it takes to rotate, so like sunrise and sunset on Mars, is strangely close to one day on Earth. It's about 24 hours and 37 minutes. It's what they call one sol. By contrast though, the year on Mars is 668 sols or 687 earth days. So a little bit less than two full Earth years.
Adam - But when it comes to Mars, people know it as the Red Planet. And that red is because of iron oxide, which is the same compound that's the rust on anything old and metal that you might have, but apart from it just being red, there are two noticeable poles on Mars, that are full of ice and solid water ice, as well at that.
Ben - Yeah. So more kind of, striking similarities to Earth in that regard. I mean, we have frosty poles as well, and even more similarities to my home country, Australia, the red dirt that is so ubiquitous here in the Australian Outback. So Mars, Australia, are they the same thing who knows.
Adam - Mars has other things on it that we might recognise as well. So it's got volcanoes. So there's volcanism going on on Mars, and Mars has the largest volcano in the solar system, which is called Olympus Mons, which is more than twice the height of Everest.
Ben - Yeah. Wow. That's a big mountain. So yeah, I mean, there's a lot of similarities, but one very important difference between Earth and Mars, at least as far as humans are concerned, is that Mars doesn't have something very, very important that Earth does. Earth has this magnetic field surrounding it called the magnetosphere, which protects us here on Earth from some very, very damaging cosmic rays from outer space, Mars possesses no such field, which would make the surface very inhospitable to human beings, because we'd just be constantly bombarded by these damaging cosmic rays. Keeping in mind, the similarities though. Another interesting thing about Mars is that unlike some other planets, it has a tilt similar to Earth, which means that it has seasons kind of like those on earth. There is a Martian summer and a Martian winter. So you can begin to get a picture of why there's been so much interest in Mars. I mean, originally when people were looking at Mars, obviously they didn't know all of these things, all of these similarities, but they were still fascinated by it. And as time has gone on and we've come to realise just how Earth like it is in many ways, you can see why it's captured so much cultural imagination for such a long time.
Adam - And the interest in Mars throughout culture is huge. I mean, when you think about H.G. Wells, writing War of the Worlds, Looney Tunes and Marvin, the Martian, Matt Damon trapped as his own Martian for such a long time, even Doctor Who has been to Mars several times.
Ben - Yeah. Which you think would be pretty boring for him, although I guess he's really, really interested in Earth for some reason. As we say, there've been all these observations of Mars, the assumed canals, which were later debunked. But despite that there's still been this persistent interest in the idea of life on Mars, pervasive throughout culture. And as a result of all of that interest, we've actually been visiting the planet since the 1960s. Albeit not in-person, but with a series of satellites and rovers,
Adam - The first missions that went visiting Mars, where the Mariner missions from the US, and the Mars missions from the Soviet Union. Mariner 4 was the first successful visit to Mars. And the Mars mission from the Soviet Union was the first thing to land on the Martian surface. But it wasn't successful. It did just plough into the surface.
Ben - Yeah. Landed pretty hard, you might say. I mean, it did land. You've got to give them that. I mean, hitting Mars from Earth, that's not easy, but perfecting rover landing technology did take a little bit longer.
Adam - And that was somewhat perfected with the Viking landers, which were the first successful landings on Mars. And then since then there've been so many missions that we've sent to look at Mars.
Ben - Some of the notable missions include Pathfinder, Opportunity, and Spirit rover, the Curiosity Rover. And of course in more recent times, you may have heard about the current mission, the US's Perseverance Rover, which comes equipped with its own helicopter. The first helicopter that's going to fly around Mars and take aerial pictures from the surface, which is called Ingenuity.
Adam - And it won't just be the U S sending rovers to Mars. Soon enough, the European Space Agency is also sending up ExoMars, which has its own Rover, which they've called Rosalind Franklin. And of course you can hear about all these rovers, and the technology, and the space missions to Mars, on our sister show Space Boffins.
Ben - All of these different missions are, among other things, I mean, they're looking for all kinds of stuff. Some of them are measuring Marsquakes, like contractions and expansions in the Martian surface, similar to earthquakes. Many of them are looking among other interesting markers, for signs of life on the red planet, and perhaps slightly less, shall we say, perhaps slightly less sensationally. They are also looking for signs of water, because this has long been one of the main points of our fascination with the red planet. Is there specifically liquid water on Mars? And it's not hard to understand why we've been so interested in whether or not there could be liquid water, because so far, all life, as we understand it, all organic life requires water. So as we mentioned earlier, we know there's frozen water on Mars, but is there still any liquid water present on Mars today? And what was the state of Mars's moisture in the past.
Adam - To learn more about that, Ben and I were joined by Lujendra Ojha, who's part of the team that discovered some of the most compelling evidence for liquid water on Mars. We started by talking with him about why Mars fascinates humanity.
Lujendra - It seems to be going forward. And then it sort of like, goes backward. And it just like, does this dance. That was very interesting because what happens is, as Mars and Earth are going around its orbit at some point, you know, Mars is ahead, but then Earth overtakes it. And so when we look at Mars from Earth, it kind of looks like Mars does this dance. So, you know, even for that, Mars was really interesting going back 2000 years, it's a red fiery star.
Ben - So even ancient people would have noticed that, is that the implication there that, like, it was just doing a cool thing in the sky that other stuff wasn't doing?
Lujendra - Yeah. So even people were fascinated back in the day and, in the earlier 20th century, there were a lot of novels about Mars, right? I mean, there were these like Mars Attacks, the Martian Chronicles, the Green Men, everything War of the Worlds, you know. And so that led to this fascination about, Oh yeah, Mars might have these creatures. People believed that when we go to Mars, we're going to find skyscrapers. We're going to find green men. And there was just a lot of fascination. We went there in the 1960s with the missions, and it just turned out to be this cold desert-like planet, you know, it was much more like the Moon than Earth. And so that dream was shattered. And then a couple of decades later, these landed space missions happen on Mars. And that has reinvigorated this interest in Mars. So it's got a really fascinating story, but I think in the end, it's just, it's so much Earth-like when you look at the history, that that's really the reason why people are so fascinated with Mars.
Ben - Because it's nearby and it's similar to Earth. Is that what you're saying?
Lujendra - Yeah.If you look at the planets that are in the solar system close to us, there's Mercury right. Closest planet to the Sun, and in terms of life being there, it's extremely difficult, let's say. It's right near the Sun, the temperature fluctuations are crazy. There is no atmosphere. Venus is hellish hot, in terms of looking for signs of life, either present or past it's completely just not a great candidate. Then you have Earth, the sole planet that has life. And then really the only planet, not counting the moons of Jupiter and Saturn and whatnot, but the only planet that is even remotely capable of ever supporting life is Mars. And I think that's really the reason for the fascination.
Adam - Well then, I suppose then the next one is, we talked about why we like Mars, but how did we get into the idea of there being water there potentially?
Lujendra - When you look at Mars through a telescope, so forget about spacecraft, right? Even back in the early, 1910s and 1920s, people were looking at Mars through their telescopes. And what happens with Mars is that it's very active in terms of its dust. And so if you were to look at Mars on, let's say, 1910 January, and then, let's say in 1912, you look at Mars again, a lot of these patterns in Mars would change. The darker areas would get lighter. The lighter areas would get darker. So there's a lot of colour changes happening. So even before we ever went with the spacecraft, there were these colour changes happening, because of dust. That led a lot of people, a lot of the early scientists, to propose that there was either, water sublimation deposition happening, or also that these colour changes we were seeing in Mars was because of vegetation, right. When you have a forest that's blooming, and when the forest is completely devoid of any leaves. So there was always a speculation. And then much later during the spacecraft era, when we went to Mars, of course we did not find any of these skyscrapers or modern technology. But what we saw was these long channels that look like Earth rivers. In the Southern hemisphere of Mars, there are thousands and thousands and thousands, hundreds of thousands of these channels, that look like little valleys carved by running liquid water. And so that was the first telltale sign. Since then we have flown, can't even keep count, like how many spacecraft, and there's no ambiguity that there was water. I mean, we find clay, like you have these instruments called spectrometers, which are very sensitive to the chemical minerals that are on Mars. So we found clays, we found other minerals that require liquid water. We find deltas. These are deposits made by running water. You see features like that on Mars. I mean, there's evidence of floods in Gale Crater. Landed missions, satellites, and even telescopic observation. I mean, they all point to the fact that Mars had tons and tons of liquid water in the past. Most channels on Mars are relatively smaller, but still, I mean, you know, there's this one river on Mars that is 40 kilometres wide. So think about Earth, right? What is the widest river you've ever seen? Maybe a couple kilometres, maybe at maximum 10 kilometre. There are some channels, the width of which is like 40 kilometres. And so it boggles my mind that, how do you carve a channel that is 40 kilometres wide? How much water would you need? I mean, you need a mega mega flood for something like that.
Adam - I mean, that's big enough that you'd have trouble seeing the shore on the other side.
Ben - Like an ocean more than a river. Okay. So some indirect evidence, right, for years and years and years. Right. But, obviously at a certain point there were observations made that confirmed the presence of water on Mars. So when did that occur?
Lujendra - It sort of gets philosophical where, you know, some might say, okay, well, what is the unambiguous, like direct evidence? Right? Most of our direct evidence comes from what we call remote sensing instruments. So remote sensing, just like the word implies, it's sensing something from a far away distance using satellites. And so one of the first direct, which I would describe as being spectral evidence, or in other words, we look at the surface of Mars in different colours, any minerals that bear water, they absorb light differently than minerals that don't have water. And so the first spectral indication that there were these water absorbing minerals, was the mid-2000s, that showed that there were all these clays, and sulfates, minerals on the surface of Mars. And it was telling us about the early history of Mars, where there was a lot of water, but even without going there, we know that there's water on Mars because you can see the polar caps.
Adam - Was that like the direct evidence then that we've come across?
Lujendra - One could say that, okay, the only direct evidence that I accept is holding a glass of water that's made on Mars. Right. And that's not going to happen anytime soon.
Ben - Well, Elon Musk might be working on that, might be selling us bottled Martian Spring, by 2026, apparently, I've heard.
Adam - There are numerous Sci-fi things of don't drink the Mars water. So many.
Lujendra - There's a lot of cool stories about what Martian water might really be like. Because one of the things that we find is that Mars has a lot of salts. In particular, there are these salts called perchlorates, and if these salts are present in the water, it might actually be not so great for your body. On earth, perchlorates cause a lot of thyroid problems, they can also be used as rocket propellant. And so if that salt is really present in the water, yeah. It might not be, you got a lawsuit in your hands.
Ben - Well, I understand that you yourself have been involved in some of the work that many people consider the concrete evidence of water on Mars. Can you tell us a little bit about that?
Lujendra - There's absolutely no doubt, now that there is water on Mars, in the present day. But what is sort of doubtful is whether that water can ever turn into a liquid state.
Ben - So we know it's there in the past. The question is whether it's still there today or whether it's just existing in gas and ice.
Lujendra - Right. Exactly. Because Mars is relatively cold. The atmosphere is not strong enough. Even if you were to take, for example, a glass of liquid water, what would happen is that because the atmosphere is not very conducive to the stability of liquid water, that water would rapidly evaporate or freeze. So liquid, in the liquid state, that is the key, right? Which is really what life requires, is a liquid agent, liquid water. And so that's why it's been debated. That's why it's been talked about so much. When I was an undergrad, I was looking at these things called recurring slope lineae. And when we first found this feature, I was an undergrad at that time. And I was like, one of the first one to work on these features. Everything that we knew at the time, was telling us that this might be an indication of liquid water on Mars. That's a pretty bold statement to make, to say that, you know, in this sort of cold, frozen planet, you can have water in liquid form. And it's been something that we've been still researching. We're not completely sure what the heck they are, but it's probably, I would say the best candidate for liquid water on Mars. Initially, when we started talking about these features, when we first started studying these features, there were a lot of us that were convinced that liquid water does and did play a role. Now it's getting a little bit more confusing. And so we still need much more proof to really make sure, to really say that this is liquid.
Ben - I remember I was an early undergrad myself when that announcement was made. And I remember sitting up all night watching that press conference about the announcement. It's incredible stuff, but just for those who might not have seen it, what are these recurring slope lineae, and how do they tell you about the supposed presence of water?
Lujendra - So the word recurring slope linear, we came up with that name because these are tiny little black lines. They're pretty small. So only the highest resolution camera we have on Mars can image them. The highest resolution camera that we have on Mar, it's called HiRISE camera. And so one of the things that HiRISE can do is image the same place multiple times. So every couple weeks, every couple of months, we can go back to that same little crater or same little canyon on Mars and image it. And it just happened that in a lot of these places on Mars, there are these tiny little lines. They're maybe about a metre wide or so, and they increase over time. So if you take a picture at time zero, and then you take a picture at time one, and then another picture at time two, what you would see in those three images are these tiny little lines that are forming, growing a little bit, growing a little bit, growing a little bit. And then at some points completely fades. And they form only in the steepest of the Martian terrain, they don't form in a flat land. And it just so happened that when we started noticing these features, they were only forming when it was really, really hot on Mars, in the Southern summer. Mars has this tilt in its orbit, much like Earth. So Mars has seasons. And so Mars has Southern summer. Mars has Southern winter. Most of these RSLs were forming in the Southern summer. When you put all this evidence together, right? So these are little lines that are flowing downhill and much like what you would expect water to do. And then initially it seemed like they were only forming during the summer. And so logically to us, it made sense that, you know, water may play a key role in this, and everything seemed to be telling us that, Hey, you know, water plays a role in this feature, and now we're not quite sure what they are.
Ben - The theory was at the time, melting ice water rolling downhill?
Lujendra - Yeah. Melting water ice, or there is another process called deliquescence. So I was telling earlier about these salts called perchlorates. So perchlorates, what they can do is if there is atmospheric moisture, if it's really humid, what they can do is they can absorb the water from the atmosphere, and turn itself completely into liquid. And so this deliquescence process is something we see all the time in, for example, Antarctica, or in the Atacama desert on Earth. So that's another thing that we think might happen on Mars, is that if you have big enough salt, especially these perchlorate salt, they can turn into liquid just by absorbing the water from the atmosphere.
Adam - Why would it be such a big deal if we did find water on Mars? What's the importance of it?
Lujendra - Yeah. I mean, you know, we've already found water on Mars. We have a running joke that, you know, anytime someone says they've found water on Mars, we say, well, congratulations, you're the 10,000 person in history to find water on Mars. It's just one of those sexy topics that everyone uses all the time. And they're like, Oh yeah, we found water on Mars again.
Adam - Yeah. The NASA announcement is always "NASA has an announcement. It's not aliens."
Lujendra - Right. Right. It comes back again to this idea of habitability. I mean, if you think about the number of planets we have in the solar system, and the number of planets that have liquid water, you know, leave life, but look at water. There's only one, right? I think it would mean a lot for habitability, but also, you know, in this day and age, when we're finding so many exoplanets in the other star systems, right? Every time you go out and look at a star, every star has a planet, two planets, maybe, a planet system, much like our own. Do you think in terms of probability, if there is a probability that two out of seven planets in each star system has water, right. And one out of those two planets has life. Then you can do this back of the envelope calculation to say, okay, in the billions and billions and billions of stars, what is the probability that there's life. Finding water on Mars sort of helps us constrain those parameters a little bit. And there's of course this big picture thing about, well, if it has liquid water now, chances are for a long time in Mars's history, there was liquid water. And so did it ever have the ingredients, much like on Earth to go through this genesis, and then proliferation of life, or is this idea of having liquid water as a condition for habitability, just a misnomer. And it's just what we're used to. And we think that that's absolutely incredibly important, but chances are, you know, Mars had tons and tons of liquid water, but it never led to any sort of proliferation of life. I think it just helps us understand, I mean, our own origin more than anything.
Ben - Hm. Something about how life forms, how likely it is to form. We can learn from knowing about Martian water. What do you think about the prospects for microbial life in Martian water?
Lujendra - We see crazy extremophiles, right? Extremophiles are these lifeforms on Earth that live in extreme conditions, extreme situations. Life has a way to defy everything and evolve.
Ben - To quote Jurassic Park...
Adam - The great Jeff Goldblum!
Lujendra - The issue again is having this continuous availability of liquid water, which is really the problem, like even going 4 billion years ago. Right? One of the issues is that the Sun was much fainter 4 billion years ago. Yet we see this evidence of liquid water on Mars. And there's a lot of questions about that. Like, it's called the Faint Young Sun paradox. How did Mars have liquid water? And one of the ideas that Mars had liquid water for a brief amount of time, just because there was enough heat being produced inside of the planet. So the melting of ice into water did not happen from the Sun's sunrays, but it actually happened because Mars was relatively hot from geothermal heat. So if that is the case, then, you know, liquid water only existed on Mars intermittently. It doesn't seem like Mars had this continuous presence of water for a long time. And I think that's going to be a really big stress on life, not having this continuous availability of liquid water. And so I, myself am a sceptic, but I'm also not a biologist.
Ben - Fascinating stuff.
Adam - I guess the other big one is; there's all this water on Mars. Where did it come from? How did it get there in the first place?
Lujendra - You can ask the same question about the Earth too, right? I mean, the Earth has a lot of water. Where did all that water come from? There's two ideas about that. The one is that, you know, all these planets started with the same sort of basic ingredients, right? So that water is primordial, that the water was there when the planets formed. And then when volcanism happened, when there were a lot of gases being released from the inside of the planet, that's where the water came from. The other idea is that they were additions, much later. So we have asteroids colliding with Earth, and Mars for that matter. We have comets colliding with these bodies. And so they could be a late stage addition. There's not really a really good consensus as to what would have been the primary source of water. I think both played a major role, both late addition, and the fact that, you know, we started with having water from this cosmic debris that formed the planet, but which contributed to the most water is quite unknown.
Adam - So what's the future of this kind of work, of looking for water on Mars. What's the next thing we're going to be doing, or the next big breakthroughs?
Lujendra - For a lot of people, the idea of terraformation of Mars is really fascinating. There's a lot of interest from the private side and, you know, the general public about terraformation of Mars. And then that's something that I think will fascinate a lot of people's minds. And in particular, one idea is that well, if you had enough, let's say carbon dioxide, trapped as ice or water trapped as ice, and if you could somehow liberate all that ice into the atmosphere, then you could have this really strong atmosphere in Mars that could potentially allow greenhouse warming, and make Mars habitable, again. For example, Elon Musk has this idea of nuking Mars. So you send two nuclear warheads into the polar caps of Mars and melt all the ice. And you know, all the ice will go into the atmosphere. Both water and CO2, carbon dioxide. They're called greenhouse gases. So over time in principle, this should lead to warming of Mars. Well, people have run this number, and it's nowhere close, right? It's absolutely nowhere close. From what we currently know about all the water trapped in the subsurface and the polar caps and minerals. Doesn't matter, even if you take a hundred percent of the water out of the surface, put it in the atmosphere, it's still nowhere close enough to make Mars habitable. It's bad news for terraformation. And so, you know, I think the idea of stability of liquid water for future humans, I think that's going to be the next step. And people have been talking about, for example, living in the Martian caves, Mars has a lot of caves, so you're deep underground. And so that might be a little bit, much more stable place for water to exist, for humans to live, there's questions about, Mars lacks a magnetic field. So even if you have atmosphere, over time, if you don't have protection from a magnetic field, that atmosphere is just going to be stripped away by the harmful rays from the Sun. These are the questions that's going to baffle the next generation of Martian scientists.