Mars Gullies Aren’t Made by Water: The Surprising Dry Ice Answer | Space Nuts: Astronomy...

[00:00:00] [SPEAKER_01] Hello, thanks for joining us. This is Space Nuts, a fresh crisp episode for you to devour, I hope. My name is Andrew Dunkley, your host. Great to have your company. A bit of a water theme in this particular episode, or partly. There's a question being raised in space science about what causes the gullies on Mars. Well, we know that gullies are caused by water flows and rainfall on Earth, but that can't be the case on Earth.

[00:00:29] [SPEAKER_01] Can it? Well, they think they've figured it out and it's quite a surprising thing. We're also going to look at water on the moon or the lack of which could threaten future cities and the search for ocean worlds. They think they know how. We'll tell you all about it on this episode of Space News Today.

[00:00:49] [SPEAKER_03] 15 seconds. Guidance is internal. 10, 9, ignition sequence start. Space Nuts. 5, 4, 3, 2, 1, 2, 3, 4, 5, 4, 3, 2, 1. Space Nuts. Astronauts report it feels good.

[00:01:04] [SPEAKER_01] To help us with all of that is Professor Fred Watson, astronomer large sporting his new knee because he wanted to be kneeded.

[00:01:17] [SPEAKER_02] Oh, dear. That's all right. That's as good as they get today, I think.

[00:01:25] [SPEAKER_01] It's, you know, that's dead joke. That's just beyond a dead joke. That's worth.

[00:01:34] [SPEAKER_02] So it was three weeks ago yesterday that I got my new knee. So progress is happening. I am walking pretty well now. I have yet to have my first drive in the car, but that'll be this week, I think. I'm told that I'm allowed to do that now. I'm off the high-intensity medication. And so far, so good. There was a bad week last week when things took a turn for the worse

[00:02:02] [SPEAKER_02] because I had an allergic reaction to the dressings that were on the knee. Gosh, that's nasty. That can be quite dangerous, it turns out. They didn't tell me that until after they'd fixed the problem. So, yeah. Anyway, so it's all good. Everybody's happy at the moment.

[00:02:18] [SPEAKER_01] Yeah. The only downside is you've got the hybrid knee, which means every night you've got to plug it in to charge it.

[00:02:25] [SPEAKER_02] A bionic knee would be good for that. You could perhaps get up to speed a bit faster than I do at the moment. But no, it's working very well. All credit to the team who did the job, Dr. Parker and his friends and stuff. We had a great time.

[00:02:40] [SPEAKER_01] It reminds me of something my son told me about because he's always online looking for the next weirdest thing. And he said the Chinese, I think the Chinese have invented an exoskeleton that you can wear that will walk for you so you don't have to make the effort. Yeah. And run. Oh, my goodness. Yeah, they're good. Isn't technology going in strange places? In weird directions, that's right.

[00:03:05] [SPEAKER_01] But that, I think, is going to be great for people in the future who have paralysis problems or... Yeah, profoundly disabled, that's right. ...that sort of thing. And probably good for rehabilitation, who knows? Maybe. Yeah, maybe. All right. Let's talk about these stories that are in the news at the moment. And the focus is on Mars.

[00:03:31] [SPEAKER_01] In terms of images of Martian gullies, now, a lot of things about Mars are so strikingly similar to Earth. The canyons and the ocean beds and all that. The only thing lacking is, well, you know, a breathable atmosphere, liquid water on the surface, weather, etc. Gravity. But the question has come up as to what causes the gullies on Mars. Now, my first thought was, well, hang on a minute. They were already there. I mean, they happened billions of years ago.

[00:04:00] [SPEAKER_01] And that was when water was liquid on the surface. But they've been changing without water. So what's going on?

[00:04:12] [SPEAKER_02] Indeed, that is a good question. So probably you and I spoke about gullies on Mars a long time ago, because there was a time when it was being suggested that some of these gullies were due to the fact that on the equator on Mars, in the Martian summertime, you can actually get temperatures that are high enough for liquid water to exist.

[00:04:38] [SPEAKER_02] And the theory was that maybe, you know, there's a permafrost of ice that come midsummer, it melts, and you get these water flows down slopes, which are what cause the gullies. Gullies, I guess they're, you know, they're the beginnings of rivers, really, in a way. They're the sort of little gentle impressions in a landscape, which are made by flowing water,

[00:05:04] [SPEAKER_02] which always wants to go downhill, and eventually you carve out a river valley. But as you say, some of the early observations, I think, with Mars Reconnaissance Orbiter, with Mars Express, those two venerable orbiting spacecraft, it was quickly realised that these things change on a seasonal basis. And that was why the thinking was that maybe there's enough water to do it.

[00:05:29] [SPEAKER_02] However, it turns out that you get these gullies in regions of Mars where the temperature never gets high enough for liquid water to exist on the surface. In other words, you know, the higher latitude regions, the regions towards the poles. And so what has happened is that a group of scientists, actually in one of the Parisian universities in France, they've looked at the alternatives for water.

[00:05:57] [SPEAKER_02] So ruling out water, you can do it because we know what the temperature is, we know what the pressure is. It's just not possible for liquid water to exist in some of these regions. But they did actually go even a step further. They looked, from the data from Mars Express and Mars Reconnaissance Orbiter,

[00:06:21] [SPEAKER_02] they looked at the spectrum of some of these melting ice fields where you're looking really near the poles of Mars, where some of these gullies are. And they found there's no signature for water. In other words, water ice is definitely not a player, or liquid water is definitely not a player in this story.

[00:06:49] [SPEAKER_02] And so the alternative, which we know is present on Mars, and we know that at least some of Mars' polar ice caps are made of this, is solid carbon dioxide or carbon dioxide generally. We on Earth are familiar with solid carbon dioxide as dry ice. On Mars, it does exist. We know there's a frost of dry ice near the poles.

[00:07:15] [SPEAKER_02] But because the pressure is lower on Mars, it's got slightly different mechanisms of behaviour. So it is possible for dry ice. Dry ice on Earth just sublimes. It goes straight from a solid to a gas. But I think under certain conditions on Mars, it can be liquid for a short time. So what's the story?

[00:07:39] [SPEAKER_02] These researchers had two theories, which were to try and explain the origin of the gullies. One is something which is a geyser mechanism. The idea is you've got geysers, which we're familiar with as jets of hot water, coming up from underneath the surface of Earth, being heated by magmatic heat.

[00:08:08] [SPEAKER_02] I think both of us, you and I, Andrew, have been to the place that gives those things their name, geyser in Iceland. Did you visit the geyser there? Oh, yeah. Yeah.

[00:08:19] [SPEAKER_01] Yeah. Actually, the best one I've ever seen was in New Zealand.

[00:08:22] [SPEAKER_02] Yeah.

[00:08:23] [SPEAKER_01] There's a massive one there at Rotorua.

[00:08:25] [SPEAKER_02] Wow. Rotorua, that's right. Yeah. So anyway, we don't call them Rotoruas. We call them geysers. That's because of the one in Iceland. So what's the theory there? The theory is that you've got basically a sheet of dry ice, of solid carbon dioxide, that forms in the wintertime.

[00:08:50] [SPEAKER_02] And as spring comes, the heat passing through that sheet of dry ice basically warms up the soil underneath. And that turns some of the ice, this carbon dioxide ice, into gaseous carbon dioxide. So you've got a buildup of pressure underneath the sheet of ice.

[00:09:12] [SPEAKER_02] And eventually, the ice basically ruptures, bang, and out comes this high-velocity jet of carbon dioxide. And the theory is that that takes a lot of soil and dust and stuff with it. And that gives rise to the gullies. It gives you basically the discoloration that we see in the gullies. And that is a mechanism that they looked at.

[00:09:40] [SPEAKER_02] But what has caused them to discard that idea is that the geyser action would appear around the spring equinox on Mars. But you don't see this gullies activity, these darkenings of the gullies until later in the year.

[00:10:06] [SPEAKER_02] You don't see them until getting on almost for the Martian summer when those geysers should have shut down. So they ruled that out as the origin. And this is the start of what they looked at instead, which is something a bit similar.

[00:10:27] [SPEAKER_02] But rather than a sort of explosive process with the carbon dioxide sort of bursting out from underneath these sheets of dry ice, what you've got is the idea that there are small cracks in the ice, but there's nothing big. But what happens instead of the gas bursting out through a large crack in the ice,

[00:10:55] [SPEAKER_02] the gas stays underneath the sheet of ice, but kind of lubricates it. So that you've got essentially a floating sheet of dry ice. And of course, gravity takes over. So it slides down the slope and actually can cause the appearance of these gullies. And so that's their current favourite theory for how these gullies form.

[00:11:22] [SPEAKER_02] And their modelling shows that in the end, what you've got is exactly what we see in the gullies on Mars. And they make a comment that Earth-like features don't always require Earth-like physics. I think that might actually be a comment from Universe Today, which is where this article comes from. An old friend of ours, Universe Today, with Fraser Cain and others involved with that.

[00:11:48] [SPEAKER_02] So no liquid water on Mars, but dry ice gullies, perhaps.

[00:11:53] [SPEAKER_01] Yeah, I like the way they describe it for people like me to get into our heads what might be going on. They call it the air hockey effect. Yes. If anyone's ever been to an arcade and played air hockey, it's played on a table with lots of little pinholes in it blowing air up, which causes a disc to be able to hover when you hit it. And that's what they think might be the effect that's changing and causing the gullies on Mars.

[00:12:22] [SPEAKER_01] So really fascinating, really fascinating. The other effect is comparing a human bodily function. It's not as big and powerful as a trumpet, but it could be a silent but deadly.

[00:12:40] [SPEAKER_02] I'm going to leave that one completely alone, Andrew.

[00:12:43] [SPEAKER_01] I'll just leave that one hanging in the air, Fred.

[00:12:45] [SPEAKER_02] Yes, you would, yes. I'm afraid we've got a dog that does that. You don't see that side of Geordie's personality, but we do.

[00:12:54] [SPEAKER_01] Hearing him's enough.

[00:12:56] [SPEAKER_02] Yes, it is, yeah.

[00:12:58] [SPEAKER_01] Oh, gosh. But no, it's fascinating. And if you want to read about it, universetoday.com is the website where you'll find that very interesting story. This is Space Nuts with Andrew Dunkley and Professor Fred Watson. Our next story takes us from not water on Mars to a particular lack of water on the moon.

[00:13:25] [SPEAKER_01] And the reason they're saying that is because of, you know, the potential for people living long term on the lunar surface. And up until now, they've thought, well, there's a ready supply of water. Everything will be fine. We can build a million person city there. And, yeah, it'll be great. Now they don't think that's the case. They don't think there's nearly enough water to sustain even a small city on the moon.

[00:13:54] [SPEAKER_01] So what's going on there, Fred? And there's Geordie.

[00:13:59] [SPEAKER_02] Yeah, Geordie just making a comment there. So, thank you, Geordie. Very timely. Yeah, one day we'll, I hope you'll end up on the moon.

[00:14:12] [SPEAKER_02] So, yes, we've got, and look, the whole, it's really interesting the extent to which our exploration of the moon in terms of human landing is focused on this idea of there being copious water on the moon. I'm doing a talk this weekend at Macquarie University. I'm their keynote speaker for their open astronomy night, which I'm very honoured to be doing.

[00:14:38] [SPEAKER_02] And it's my talks about the future of Artemis and other ventures to the moon. And it all focuses on the southern polar region of the moon, where there is a cluster of quite deep craters which never see sunlight because they're at the South Pole. The sun always misses their depths.

[00:15:08] [SPEAKER_02] Some of them are quite deep. The one actually at the South Pole, which is called Shackleton Crater, that's four kilometres deep. It's 20 kilometres across. And the evidence from previous space missions is that there is water ice in the base of these craters that may be billions of years old, Andrew, because it's never seen the sun. So, it's never been, you know, warmed up enough to turn into a gas.

[00:15:33] [SPEAKER_02] And the temperature in some of these craters is extremely low, minus 200 or thereabouts. So, it's frozen solid. So, we've got this whole, you know, focus now on getting spacecraft and humans eventually with Artemis 4, hopefully early in 2028, actually landing on the moon in this region. And it's quite a hazardous thing to do because the South Pole of the moon is very mountainous.

[00:16:02] [SPEAKER_02] It's got all these craters. It's not smooth sailing in terms of finding nice flat places to land as happened with the Apollo missions, which were all in much less challenging parts of the moon's surface. So, the focus on water on the moon is enormous.

[00:16:21] [SPEAKER_02] And what I don't know that it's really been looked at in great detail before, but we now have some work that suggests that, yes, there probably is water on the moon's surface,

[00:16:40] [SPEAKER_02] but there might not be enough of it to make it, you know, available on an industrial scale, if I can put that, a place where humans could survive permanently or where you could have permanent presence. So, it's a theory that really, I think, will start, you know, raising a few eyebrows.

[00:17:05] [SPEAKER_02] It's come from, I guess, the idea of just how much water there is there, you know, on the basis of the geography, if I can put it that way, the fact that you have got these deep craters.

[00:17:23] [SPEAKER_02] I think the jury is still out on just how much water there is, what form it takes, because it, you know, it could be buried under rock. We're really in a region of very big unanswered questions.

[00:17:43] [SPEAKER_02] And I don't think we've talked about this, Andrew, but Chang'e 7, which is a Chinese mission to land very near Shackleton Crater, actually, the one I've just mentioned, which was supposed to launch, actually, I think the day before my knee operation, it was supposed to launch, but it was cancelled at a very short notice with a fairly brief note from the China Space Agency.

[00:18:12] [SPEAKER_02] And that now looks as though it won't happen until 2027. But that spacecraft carried not just a rover, there's an orbiter, a rover and a lander, of course, but also a hopper, a little vehicle that will hop into craters rather than try and go down into craters on wheels. And that's the idea is to use that hopper to try and find the water.

[00:18:39] [SPEAKER_02] However, Chang'e 7, when it is launched, might be the first, we know, you know, first-hand experience, if I can put it that way, of what the water is like in these craters. Sadly, we're going to have to wait a bit longer than we thought we did, but that's one step forward. And the hopper, by the way, is unlike anything that NASA is planning for the Artemis mission. So really interesting area.

[00:19:06] [SPEAKER_02] I think we're still groping in the dark a bit, if I can put it that way, given that these craters are definitely in the dark, about just how much water there is. But it's possible that there might not be enough to make it that well worthwhile.

[00:19:19] [SPEAKER_01] You know, suppose you've got to consider the limitations in our capacity to look for it at the moment. They've only got the ability to look to shallow depths. So there could be water deeper in the moons. Yes, perhaps. Yes. That we haven't found. So there may be more.

[00:19:40] [SPEAKER_01] But based on what we know now, putting a city on the moon for, you know, hundreds of thousands of people, it's just not feasible. It wouldn't last. I think they said it wouldn't last a year. Yeah. Based on the resources that exist on current estimates. I couldn't imagine that many people living on the moon. Can you?

[00:20:05] [SPEAKER_02] No, not really. I think it's not a place you'd want to... I can imagine there being things like, you know, the outposts we have in Antarctica. I think that's a sort of reasonably sustainable model for exploring the moon. But yeah, cities of tens of thousands of people, I think, is a non-starter. Yeah. And this perhaps underlines that. That's, I guess, the point of the article.

[00:20:33] [SPEAKER_01] They do go on to say that a village of a thousand, maybe 10,000 people would last centuries, though, if they kept the numbers down. So the resources that exist at the moment are feasible to an extent. Yes. Yeah. And you also have to bring into play things like recycling of water.

[00:20:59] [SPEAKER_01] They use recycled water on the International Space Station, and I think it's got over 98% efficiency. You'd have to do that on the moon. Otherwise, you're going to go through it like a packet of salt. And... Quite. And then you've got a real problem. The only other way of dealing with it, well, two ways, would be to transport water from Earth. But do we really want to do that? Or harvest it? Yeah. Harvest it from somewhere else?

[00:21:28] [SPEAKER_02] That's the whole point of, you know, going to the moon. And, of course, this water is not just for keeping a city running. It's to act as rocket fuel for future exploration beyond the moon. Yeah. So that's one of the appealing features about it. Yeah, very interesting. And it does beg the question as to whether strategies will change dramatically once we've had a chance to see it firsthand just how much water there is there.

[00:21:59] [SPEAKER_01] Because that's still... Yeah, it might force Elon to... He's abandoned Mars already too hard. Now that the moon's lacking water, he might go... Well, we won't go there either. What's Enceladus doing at the moment? Yes, that's right. Yeah, could be that. Squirting water out. Yeah. Yeah. Well, that'd make it easy to collect. If you want to read about that, it's on the PHYS, PHYS, PHYS.org website,

[00:22:26] [SPEAKER_01] or you can read the study that was published in Frontiers in Space Technologies. You're listening to Space News Today with Andrew Dunkley and Professor Fred Watson.

[00:22:38] [SPEAKER_03] I think we need to do a little more all-weather testing. Amen.

[00:22:42] [SPEAKER_01] Space Nuts. Our final story, Fred, continues to look for water, but on a much larger scale. We've been looking for exoplanets for yonks now, and we've found 5,500 plus. But we haven't found a water world, an ocean world. And they think they now know how to look for them. I think it's the gist of this story. That's correct.

[00:23:09] [SPEAKER_02] That's right. Yeah. So, yeah, this is actually a story I like a lot because I remember being very excited back in the early 2000s, I guess, when exactly this same technique that is being discussed here was used to demonstrate that Saturn's moon Titan has liquid ocean, not liquid oceans,

[00:23:38] [SPEAKER_02] liquid seas and lakes near its north pole. And it was images made by the Cassini spacecraft in its early period of orbiting around Saturn. The problem with Titan is it's got a thick atmosphere that is almost completely opaque. And so you can use infrared to penetrate through it for a while, or to some depth of clarity.

[00:24:07] [SPEAKER_02] But the real way of exploring Titan, which is what Cassini did, is by radar. You do it by radar. And that's one of the reasons that we've been able to map these seas and lakes.

[00:24:26] [SPEAKER_02] But the way they were first detected was when Cassini, when its cameras were aimed at Titan at a time when the angle between the spacecraft, the moon, Titan itself, and the sun was such that you would get a direct reflection off the liquid surface that was thought to be near the north pole of Titan.

[00:24:56] [SPEAKER_02] And sure enough, there was what we call a glint, which is a sun glint, comes from a liquid water surface. That was detected. That's how Cassini first established that there are lakes and seas on Titan. And it was then, they were subsequently mapped very accurately by Cassini's radar.

[00:25:19] [SPEAKER_02] I've still got some extraordinary maps that came from that era showing these seas and lakes near Titan's north pole. So the question that is being asked in this piece of research that we're talking about, once again, this comes to us courtesy of Universe Today, is can you do the same thing with exoplanets?

[00:25:39] [SPEAKER_02] Exoplanets. Supposing you have a suspicion that one of the 5,500 now known exoplanets, planets orbiting other stars, if you have a suspicion that one of them might have conditions where liquid water could exist, or in the case of, as in the case of Titan, liquid hydrocarbons, liquid natural gas,

[00:26:04] [SPEAKER_02] could you use this glint technique to try and establish if you did have a water world, in other words, a world covered completely by oceans? And those things have been hypothesized. Actually, we've talked about them before, these so-called Heischen worlds. Heischen is basically a term that's been concocted to represent a world with an atmosphere of hydrogen.

[00:26:31] [SPEAKER_02] That's where the high comes from, but a liquid ocean surface, hence the Shun. So it's a Heischen world. How could you use this glint technique to demonstrate that a suspected Heischen world really was a Heischen world? So two scientists at the University of Arizona, which is in Tucson, got some good friends there, but they don't include these people. I don't know them well, or all I know is their names.

[00:27:00] [SPEAKER_02] What they've done is they've done what you might call the physics of how glints might work. And the bottom line is that it's potentially a good way of doing this, but there are certain conditions that have to be fulfilled. Because you've got to get the angles right, first of all,

[00:27:29] [SPEAKER_02] and that angle is all about the object being relatively near to its parent star. So you get this sort of grazing angle almost of the light hitting the water and then being reflected back. Now, that itself presents a problem because at the moment,

[00:27:52] [SPEAKER_02] most of the exoplanets that have been discovered are only known because they have an effect on their parent star, whether it's blocking the light of the parent star as they pass in front of it, or whether it's pulling it slightly out of position by what we call the Doppler wobble technique. These mean that you never see the planet that you're trying to observe. You just see its effect on the star.

[00:28:17] [SPEAKER_02] So really, what we're talking about here could only apply if you've got direct observations of the planet. And if you need the planet to be close to the star to get the angle right, then that's a challenge because the star is sometimes billions of times brighter than the planet that you're looking for. However, it's not impossible. And there are things called coronagraphs, which are essentially devices that suppress the light of a star so that you can look for planets nearby.

[00:28:46] [SPEAKER_02] And so what these scientists are doing is feeding this information into people who are working on something that I think is still a hypothetical spacecraft, something called the Habitable Worlds Observatory, which will look at the possibility of there being habitable worlds among some of these 5,500 known exoplanets.

[00:29:13] [SPEAKER_02] What they've done is they've fed these conditions, this information into the designers to say, yeah, you can probably do this, but you need to do this, this, this and this when you build your spacecraft in order for potential water worlds to be discovered. So quite a nice piece of research.

[00:29:31] [SPEAKER_01] Yes, indeed. I hope they do find something like that eventually. I think it would be really exciting to find a water world. Ice moons, I suppose, count because they have oceans inside them. Yes, correct. An actual planet that is covered in water, we know of only one. We do. There's got to be more.

[00:29:59] [SPEAKER_01] Surely there's got to be more. Statistically, there's got to be more. Yeah. One would think. That's right.

[00:30:08] [SPEAKER_02] Whether they are findable by our current technology is, of course, another question.

[00:30:13] [SPEAKER_01] Yeah, well, in time, maybe. But then the Vera Rubin Observatory? Who knows? We could find some things that we'd never even thought of.

[00:30:24] [SPEAKER_02] That's correct. And, of course, the Nancy Grace Roman spacecraft recently launched, which we hope we'll see results from early next year. That does have a coronagraph. So it does have a device to look at some of these planets directly.

[00:30:38] [SPEAKER_01] Yes, indeed. Very exciting times ahead. And it won't be long before we start getting some information back from that telescope either. It's on its way. Yes. So if you'd like to read about that particular story in the search for Water Worlds, universetoday.com, again, is a source that's very well worth visiting. And that brings us to the end of the show. Fred, thank you so much.

[00:31:07] [SPEAKER_02] You're welcome, Andrew. It's been a pleasure and a privilege to talk to you, and I do hope we can do it again sometime.

[00:31:13] [SPEAKER_01] I hope we can do it really, really, really, really soon.

[00:31:18] Yeah.

[00:31:19] [SPEAKER_01] Maybe soon. Catch you soon. Professor Fred Watson, astronomer at large, and while you're waiting for a new episode, please visit our website. You can send us a message as you like. We've had a couple of messages from our live audience this morning. Hello to Al in old South Wales, he said. He's just about to go to bed.

[00:31:40] [SPEAKER_01] And one from Halil, I hope I got that right, who's been inspired to venture out with his studies in computer engineering because he listens to Space Nuts. So thanks for that message. That's lovely. But yeah, our website, space nuts podcast dot com or space nuts dot dot IO. You can send us messages. You can do that through the AMA link and all sorts of other things. Visit the shop while you're there. Some new books in the shop. Yeah.

[00:32:10] [SPEAKER_01] And plenty of other things to do. And thanks to Hugh in the studio. Couldn't be with us today. We were talking about sun glints. Well, Hugh did a bit of a flashing of his own. So I've got to go down and bail him out after this. And from me, Andrew Dunkley, thanks for your company. We'll catch you on the next episode of Space Nuts.

[00:32:29] [SPEAKER_00] Bye bye. Space Nuts. You'll be listening to the Space Nuts podcast. Available at Apple Podcasts, Spotify, iHeartRadio or your favourite podcast player. You can also stream on demand at bytes dot com. This has been another quality podcast production from bytes dot com.