Planetary Radio: Space Exploration, Astronomy and Science - Are There Giant Caves on Mars?

Episode Date: June 18, 2007

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Are there giant caves on Mars? It's a deep subject, this week on Planetary Radio. Hi everyone, welcome to Public Radio's travel show that takes you to the final frontier. I'm Matt Kaplan. Their discoverers call them the Seven Sisters, black dots on the surface of the red planet that appear to be either deep pits or perhaps windows on huge lava tubes running under the surface. Either way, they have once again demonstrated that Mars continues to spring exciting surprises on us. We'll talk with

three of the United States Geological Survey scientists who found and confirmed these holes and are now trying to figure out what they represent. Later today, Bruce Batts turns the tables on you. You're used to him showing us what's up. This time, he wants you to show him a specific bit of the night sky, and your photo might win you a prize. That's along with our usual space trivia contest.

And Emily Laktawalla will be along shortly with a Q&A classic. Things are looking up, if you'll pardon the expression, on both Space Shuttle Atlantis and the International Space Station. As we prepared this week's show, NASA had cleared the shuttle for re-entry. A spacewalking astronaut stapled that troublesome thermal protection system blanket back in place. And last we checked, all the critical computer systems on the ISS were once again working and talking with each other. Several of them failed at the same time last week, causing mission controllers considerable concern. Troubleshooting continues.

Many of you will remember Mike Brown, the intrepid discoverer of distant Kuiper Belt objects. Mike Brown and Caltech graduate assistant Emily Schaller have just announced that Eris, the object formerly known as 2003 UB313, is significantly bigger than Pluto. You can read more about this story at planetary.org, where Mike reports that Eris and Pluto are otherwise almost twins. It's just that Eris is the chubby one. And a new paper just published in Nature has strengthened the case for an ancient ocean on Mars, a real ocean extending over much of the planet. That story is at planetary.org as well. Here's Emily. I'll be right back with our discussion of Martian holes. Hi, I'm Emily Lakdawalla with questions and answers. A listener asked, how does the Cassini team keep track of

where all the rings and moons are for planning all those flybys? The Cassini team has two good reasons to keep track of where the spacecraft is relative to the vast ring system and the 47 known moons. For one thing, Cassini needs to be close to an object to get good views with its cameras. More importantly, though, Cassini needs to avoid the hazards presented by Saturn's rings as it flies through Saturn's ring plane twice each orbit. Cassini always avoids the main ring system, the broad, flat A, B, and C rings. It also stays away from the twisted spiral of the F ring that orbits just outside the main rings. A bit more difficult to avoid are the G and E rings. The G ring is a very faint puff of material that lies between the main rings and the

orbit of Mimas. Although the G ring is faint, the particles in it are large enough to pose a serious hazard to the spacecraft, so Cassini avoids flying through it, though it may sometimes flirt with the edge. The E-ring extends from Mimas all the way out to Titan and is impossible for Cassini to avoid as it explores the moons. Fortunately, the E-ring is made of very tiny particles that do not pose a hazard to the spacecraft. So how do Cassini planners know where the moons are? Stay tuned to Planetary Radio to find out. Dina, Chloe, Wendy, Annie, Abby, Nikki and Jean. These are the seven sisters, black spots on the side of a massive volcano on Mars.

Lines of holes have been discovered in the past on the red planet, but their discoverers say the sisters are different. Different because none have visible walls, and only one has a bottom that has been imaged. Are they just deep pits, or could they be football field-sized skylights opening on a huge subsurface cave or lava tube? I first got a few hints of this story from U.S. geological survey scientist Jutt Wynn. Jutt was in the Mojave Desert for the spaceward-bound teacher program we covered a few months ago. He was understandably excited but unable to release the details for broadcast. Now the findings are public, so we called Tim Titus and Glenn Cushing, the findings are public, so we called Tim Titus and Glenn Cushing, USGS research colleagues of JUT in Flagstaff, Arizona, with backgrounds in astrophysics. Glenn, let me start with you, and

by the way, congratulations. I hear that you are now officially a part of the USGS as a space scientist, like your colleague Tim Titus, having graduated from Northern Arizona University. Yes, just recently. It feels very good to be a part of the team now. I bet. And it must feel good to have been the first to see these little black blemishes on the surface of Mars. It's pretty exciting once we realized that it actually was something interesting and not just funny dark spots. We had to spend a little bit of time proving to ourselves that they weren't strange artifacts or anything else. But it's very interesting stuff.

Tell us about that experience. I mean, I like these stories. I know the woman who was the first to see a volcano on Io. How was it that you saw these? Well, the first time I saw something like this, it was over a year ago, and I just found a couple of really strange dark spots, almost black spots on a Themis image. And I was doing some other research at the time, so I just kind of wrote it down on a sticky note and put it in my pile of other sticky notes. And then about a year later, I found something similar to that, and I remembered that I'd seen something before, and I dug that up, and it really looked

like we had something unusual, and we checked out the thermal images, and those turned out to be very interesting as well. And we should mention that Themis is this infrared imaging instrument on the, in this case, the Mars Odyssey spacecraft, which is mostly run by your colleague, Phil Christensen, who's been on the show several times. Yeah, he's the chief scientist for that project. And just to clarify, the Themis instrument observes in both visible wavelengths and infrared waves. Yes, I'm sorry about that.

So then what? You took this to Tim? Right. Tim, your title there, as we said, is space scientist for the USGS, part of this astrogeology team, although I guess you and Glenn both are more astrophysicists. Yeah, my Ph.D. is actually astrophysics. I did my graduate-level research looking at galaxies, and Glenn's got an applied physics master's from NAU. galaxies. And Glenn's got an applied physics master's from NAU. What went through your mind, and what were the things that you wanted to do when Glenn brought in these images of these mysterious black dots? Well, the first thing I wanted to do is look at the Themis thermal

imaging to see if, to make sure it was not an artifact in the visible. And once we looked at the thermal, we were convinced that these things were actual real surface objects and not an artifact of data reduction or something like that. And then the second thing was to try to estimate how deep minimum depths for these. Glenn looked at them in terms of shadow, trying to determine depth from shadow. I wrote a very quick one-dimensional digital elevation model profiler to try and get at how deep things that they might be using photoclinometry. And it looked like these things really were holes in the ground. One of the holes actually not only had a Themis image but had a mock image. And in the mock image, it looked like we could see the bottom.

In the Themis image, we couldn't. And so on that one, we actually were able to get an actual depth as opposed to a minimum depth. But that was the only one that you could actually see the bottom, right? The rest of them, you couldn't resolve it, which leads you to believe that it was just down too far and too dark? They're deeper than we can measure, given the illumination angles for the images that we have. And there has, of course, been talk for many years, decades if you include science fiction,

about caves on Mars and the possibility of lava tubes, which I guess are also features found on our planet, but there is this thought that maybe they exist on Mars and they could be pretty big. But if indeed these are skylights, any of them, that are giving us a view down into one of these caves, that would certainly indicate that these are big caves. Well, I really would hate to speculate on how big or how small any subterranean voids might be. While I'd like to believe that these are skylights into caves, they still could actually just be very deep collapsed pits and actually not open up into anything.

And so we really right now, I don't think we can say anything about what size of caves these may or may not be. It's as we frequently run into, there's what you'd like to believe they are and what the data can tell you right now. Right now, I don't think we can tell the difference between whether it's just a very, very deep pit or whether it happens to open up into a subterranean void, i.e. a cave. Either way, these are pretty significant findings on the surface of Mars. Oh, yeah. And you put together an abstract, which I've got in front of me, for hopefully a paper that's going to be published fairly soon, if we're lucky?

Yes. We have submitted this paper to GRL, which is the Geophysical Research Letters, and we're still waiting for acceptance. And fortunately, unlike some, there's no embargo on the story, which is how we're able to talk about it, and you can still be responsible scientists in this. And I should say that the abstract that you shared with me is pretty conservative. I know that there is excitement about this. We are joined as well by another of your colleagues there at the USGS, Wendy Jager, who is listed as a research geologist at the USGS. But Wendy, you said you're also on the science team for the HiRISE instrument. I am, and we have thus far imaged one of these

dark pits with the HiRISE instrument, and that image is now released and publicly available. And in fact, we have that image on our website, and people can see it at planetary.oregon. We'll put a link directly to that. It was one of Emily's blog entries, but we will put a link to that right where people may be listening to this show. Like my colleague Emily, I was blown away by that image, which has a resolution of something less than a meter. That is quite a camera. It is. It takes images at resolutions down to about 25 centimeters per pixel. Yet this camera, which is quite sensitive, also could not see the bottom of this pit. Correct. It didn't resolve the

bottom of the pit. It's shaded and therefore dark. We don't know whether the pit has overhanging walls, whether it opens into a cave, or whether it's just a deep vertical shaft based on this image. But we do plan to re-image this site with better lighting conditions in hopes of answering that question. So that would, again, be using the HiRISE instrument? Correct. Okay, which, of course course is on the Mars Reconnaissance Orbiter. USGS research geologist Wendy Jaeger. She and colleagues Tim Titus and Glenn Cushing will return in a minute. This is Planetary Radio. I'm Sally Ride. After becoming the first American woman in space, I dedicated myself to supporting space exploration and the education and inspiration of our youth. That's why I formed Sally Ride Science, and that's why I support the Planetary Society.

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Planetary Radio listeners who aren't yet members can join and receive a Planetary Radio t-shirt. Members receive the internationally acclaimed Planetary Report magazine. That's planetary.org slash radio. The Planetary Society, exploring new worlds. Welcome back to Planetary Radio. I'm Matt Kaplan. Glenn Cushing, Tim Titus, and Wendy Jager are all with the United States Geological Survey in Flagstaff, Arizona. We're talking with them about the Seven Sisters,

a series of pits in the side of a Martian volcano. Or are they more than just pits? Here's Wendy. You are the geologist in the group, and I guess you're a bit more skeptical of the cave hypothesis here and lean more toward these just being deep pits? I do, though I don't discount the cave hypothesis here and lean more toward these just being deep pits? I do, though I don't discount the cave hypothesis. It's completely valid, and it certainly matches the data that we have thus far,

but I think there are other options. In Hawaii, we see pit crater chains in volcanic regions, like the region that we find these on Mars, and those don't tend to open up into caves. Well, you can understand how the romantic laypeople like myself would love to think that there's a huge lava tube down there. I would like to talk a little bit about the biological implications of this, although, Tim, I guess if there are remnants of biology anywhere on Mars, maybe these aren't the best candidates, even if they are caves.

Yeah, the surface of Mars, the atmospheric pressure at the surface of Mars is only about 0.6 percent that of the atmospheric pressure on the surface of the Earth. And that's at the lower end of Mars elevation. On the top of these volcanoes, the pressure can drop to only 0.1%. And so the stability of water, even as ice, it's not very stable. It's going to sublime into the atmosphere very quickly. Temperature extremes because of the high elevation. The absolute temperature can double between day and night temperature going from cold enough where the atmosphere literally can freeze out as frost on the ground

to daytime temperatures close to, oh, Glenn, what temperatures were you getting of what, about 300 Kelvin? Yeah, they get up to about 300 Kelvin in the afternoons. And that's about, that's a fairly, that's a moderately warm day. Balmy was just the word I was thinking of. So what comes next? Will you start looking maybe in the equatorial regions and at lower altitudes? Well, yes, that's exactly what we'd like to do.

It would be wonderful if we could find such an opening at a lower elevation. And not only that, but just for the sake of exploration, we need things to be lower in elevation just to give ourselves enough atmosphere for the arrow breaking of a spacecraft to come towards the ground. At the elevation of these caves, there's no way with our current technology that we could send a spacecraft that could slow down and maneuver enough to get to these. And not only that, these are targets that are only a couple hundred meters in diameter, and usually our landing ellipses are, you know, in the range of many kilometers. Sure, sure. So they're pretty specific targets. targets. Well, as we get better at this, and let's say you find one of these pits in a much more convenient location and perhaps one much more promising for looking for biological activity or signs of past activity, what would be the answer? Coming up with some kind of rover that could rappel down into the hole? That technology is being worked on by several groups across the country.

One thing that if something like that were discovered, we would hope to have a lot of public input and demand that we go there and check these things out. But, of course, decisions for where we go and how we explore, there's a lot of engineering constraints that usually dictate those decisions. It does seem like this would make one of these a very strong candidate if you found one in a good location. Wendy, you said that you hope to target the HiRISE camera at one of these in better lighting. Are there other things as a geologist that you would like to see done, either with these seven sisters or in the search for additional holes in Mars? with these seven sisters, are in the search for additional holes in Mars?

Well, I think just imaging these regions that we've already identified under better lighting conditions would be the first step. The MRO spacecraft can roll 30 degrees to the side and image from the side. And so if we can look into an illuminated wall, that would be a very interesting observation to obtain. Tim, with just a minute or so left, I know that you and your colleague, Jut Win, are also involved in researching caves on Earth for what they might be able to do to help us find out more about possible caves on Mars. Can you talk a little bit about that and how that's being conducted? Yes. What we're doing is setting out several different, essentially, thermometers

outside of cave openings, inside the cave opening, and then deep inside the cave, and then taking hourly measurements over a period of an entire year at a variety of caves, both throughout the southwest of the U.S. and, to some extent, a couple of caves in Chile. And then this data, this temperature data, that can then be used to look at trends and comparisons between the cave opening and the surface and determine what times of day and what time of the year would be best to detect these caves if one was looking at the caves using a thermal imager from orbit. I want to thank all three of you for joining me and taking us through this really incredible discovery. And I absolutely recommend to listeners that they go to our website.

We will also provide a link to the USGS site. And take a look at these images, particularly that spectacular high-rise image, which just took my breath away. And I hope, with the pending publication of the paper and continuing research, that we'll have more to talk to you about before too long. Yeah, I think so. Thank you, Glenn. I was just waiting for somebody to jump in there. So once again, thank you so much for joining us, and we'll look forward to talking again.

Tim Titus and Glenn Cushing are space scientists with the USGS in Flagstaff, Arizona. Down the hall from them is Wendy Jaeger, a geologist, specifically a research geologist with the USGS and part of the science team for that amazing high-rise camera on the Mars Reconnaissance Orbiter. We will be taking a look at the night sky, as we always do, with our friend Bruce Betts right after this return visit from Emily.

I'm Emily Lakdawalla, back with Q&A. How does the Cassini team know so far in advance where the moons are going to be to plan Cassini's flybys? It's just good old-fashioned mechanics. The orbits of Cassini's major moons and most of the minor ones are very well known and described in detail with mathematical equations. These equations can be used to generate enormous tables of data that Cassini planners use to time and refine the spacecraft's encounters with the moons. The orbital path is tweaked in an iterative process to bring Cassini as close as possible to moons in encounters called targeted flybys. Once the targeted flybys are fixed in the orbital plan, the tables are examined again for fortuitous close encounters with other moons.

Although generally not as close as the planned targeted flybys, these other encounters, called non-targeted flybys, produce important datasets that slowly fill out global maps of all of Saturn's moons. Got a question about the universe? Send it to us at planetaryradio at planetary.org. And now here's Matt with more Planetary Radio. Time for What's Up on Planetary Radio. Bruce Betts, the director of projects for the Planetary Society, is here to tell us about the night sky and the first thing that ever went into space,

at least the first human-created thing. I think we're going to get to that. Welcome. Gosh, I hope so. That'd be good. But let's start with non-human things in space. Of course, Venus dominating the West in the early evening, and we're coming up on that thing I keep teasing. June 30th and July 1st, Venus and Saturn getting to within one degree of each other. And I'm going to solicit something in case any of you are out there who might be interested, which is, hey, take a picture of them together off on the horizon.

Put something in the foreground. If you have most cameras, I've got a fairly inexpensive digital camera, and you can get something with this if you set it on some type of night shot or control your exposure. Stick it somewhere solid and get a picture of anything from a giant fish to the Eiffel Tower in the foreground. We'll make it spiffier. Send it to us. Send it to where you can send the trivia

contest, and if we get anything nifty, we'll put it up there, and if we really like it, hey, we'll even come up with a prize. Excellent. It won't involve a giant fish. And you don't care. I mean, we've got a lot of amateur astronomers out there. It can be astrophotography or just somebody with a point-and-shoot. Exactly. I'm kind of envisioning the point-and-shoot,

but astrophotography is fabulous, too. I would bet that the more we are-and-shoot, but astrophotography is fabulous, too. I would bet that the more we are entertained by what's in the foreground, the better. Oh, yeah. I love that. But I'm flexible. I love it. Okay, good. Well, you can compete, too.

The email address is coming up a little bit later, and I don't think I'm eligible. But anyway. So what's up? Well, I'm kind of encouraging people to explore outside maybe their realm because you can do it with a regular camera. Outside the box. Outside the camera box, yes. What's also up is Jupiter, if you turn your head around slowly, don't hurt yourself. And on the other side of the sky in the early evening in the east, you will find Jupiter looking also like an extremely bright star. I should say Venus is the super bright looking star-like object, and Saturn will be the also bright but not nearly as bright planet that's nearby. And if you follow a line between the two, you'll end up roughly at the bright star Regulus.

Pre-dawn, still got Mars, and you can catch, depending on when in the pre-dawn, you can catch Jupiter in the west if you're up early, early enough. Otherwise, Mars hanging out in the east before dawn. And eventually, give it a few months, it will brighten up. Sort of starting to get there. And that's our night's go. I want to mention, and we discussed this, with Vesta, the brightest asteroid, that conceptually you could see with the naked eye in a very dark sight these days at a magnitude 5.6.

Be tough, but you can at least pick it up with binoculars. It is in Scorpius, but you're going to want to pull out a sky chart and find plenty of these on the web if you look up Vesta and Sky Chart or some such thing, and you can actually see it. It's kind of neat. Don't get a chance to see an asteroid. Well, you do, but you have to go out and look for it. So go see Vesta. In the meantime, let us go on to this week in space history. 1983, our friend Sally Ride becomes the first American woman in space. Yeah.

24 years. Go on. On to Random Space Fact! You turned me on to this too, Matt. I'm just inspired by you, this show. And Terry's, let's talk about big, giant, super, giant, red, and Terry's. It is the bright star in Scorpius, and you can see it up above Jupiter right now.

And you sent over some spiffy diagrams. Yeah, yeah. Let's talk about how big it is. It is about 700 times the diameter of the sun. That's big. That's big. That's big. It's outer surface, if it were in our solar system where the sun is, its outer surface would be out past Mars. Yeah, and this was the thing I sent you.

It was kind of a goofy, you know, email spam thing. But it was fun. And it had, there was big Antares, and the sun was like one pixel. And the Earth, no, Jupiter would be far too small to see on that scale. And, you know, my favorite random space fact, which is why I can't use it but say it all the time, is we've got about 1,000 Earths inside Jupiter, and you can fit about 1,000 Jupiters inside the sun. Well, you could fit about 343 million suns inside the red giant Antares. And for those doing the math at home, that would be about 343 trillion Earths.

Ah, it boggles the mind. It boggles, boggles, boggles the mind. And yet, it's pretty under-dense being that super fluffy, super red giant thingy. So it's about 15 to 18 solar masses. On to the trivia contest. We asked you what was the first human-made object in space. And you did not have to give a year. I know some people did, because there seems to be a little debate on that. But what type of object it was does not seem much in debate. General agreement on what the object was, von Braun's first baby there, the A-4, or better known as the V-2 rocket.

Now, some people said 1942, but you pointed out, and I've read some of the history of this, I don't think so. 1944, much more likely, but it doesn't matter, the V-2 rocket. And if they didn't make space, the Americans took some and launched one in 1946. rocket. And if they didn't make space, the Americans took some and launched one in 1946. Yeah, yeah. By that time, we called it the Corporal, though. Couldn't go with V2 anymore. It was a German trademark, I think. And so that was it. Now, a couple of people did say Sputnik, but we said it didn't have to go on orbit. So yeah, there you go. People did point out that Big Bertha, the Paris gun from World War I, 42 kilometers. That's how high its shells would reach. Isn't that amazing?

Not space, but truly, truly amazing. Yeah. Wow. Okay. All right. You want to know our winner? No, I haven't said the winner. Well, it's too late.

It's Olivia Lassaux. There. Where's she from? Did I say Olivia? I'm sorry. It's Olivier. Olivier Lassaux from Honolulu, there. Where's she from? Did I say Olivia? I'm sorry. It's Olivier. Olivier Lassaux from Honolulu, Hawaii. And Olivier is a past winner.

So congratulations, Olivier. You did it again. Wins Planetary Radio T-shirt. And if you want to win your Planetary Radio T-shirt answering the following question, there are, as you know, about 365 and a quarter solar days in an Earth year. How many sidereal days are there in an Earth year? How many sidereal days? Go to planetary.org slash radio to find out,

and we'll talk all about the difference in a couple weeks when we give you the answer. You got till the 25th of June, Monday, 2 p.m., June 25. And you can also go there to find out how to get us your fabulous picture. Oh, that's right. Yeah. Thank you for the reminder. Sidereal. I always think of sideshow.

How many sideshow days are there in a year? That's exactly what I'm asking, Matt. Okay. We're done. Okay, everyone. Go out there. Look up in the night sky and think about circles. Lots and lots of circles.

Drawing circles in the sky. He's Bruce Betts, the Director director of projects for the Planetary Society he joins us every week here for What's Up? Circling the Wagons Planetary Radio is produced by the Planetary Society in Pasadena, California have a great week everyone Thank you.