Planetary Radio • Jan 19, 2022

Curiosity rolls on: Mars Science Laboratory project scientist Ashwin Vasavada

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Ashwin Vasavada

Mars Science Laboratory Project Scientist for Jet Propulsion Laboratory

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Bruce Betts

Chief Scientist / LightSail Program Manager for The Planetary Society

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Mat Kaplan

Senior Communications Adviser and former Host of Planetary Radio for The Planetary Society

We are approaching the 10th anniversary of Curiosity’s arrival in the Red Planet’s Gale crater. The rolling laboratory is still making profound discoveries as it reveals beautiful vistas and closeups. Project scientist Ashwin Vasavada shares some of the most significant finds in the last year. We’re deep into winter in the northern hemisphere, making Orion, Mat Kaplan’s favorite constellation, hard to miss in the night sky. Bruce Betts tells us there’s much more to see in this week’s What’s Up.

Morning and Evening from Mt. Sharp
Morning and Evening from Mt. Sharp NASA's Curiosity team made this artistic interpretation of the rover's view from high up Mt. Sharp by combining pictures taken at different times of day and adding colors to bring out the contrast. The first set of images was taken at 8:30 a.m local Mars time on Nov. 16, and the second set at 4:10 p.m. The morning light is highlighted in blue, while the afternoon is orange.Image: NASA/JPL-Caltech

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Mat Kaplan: Curiosity rolls on across Mars this week on Planetary Radio.

Mat Kaplan: Welcome, I'm Mat Kaplan of The Planetary Society with more of the human adventure across our solar system and beyond. Mars Science Laboratory Project scientist, Ashwin Vasavada is back to tell us what that 10-year old rover has been up to, discoveries, beautiful images and enormous amounts of data from its 10 instruments. Curiosity has also lately been paving the way for the humans that will someday walk on the Red Planet. Later will check in with the society's chief scientist, Bruce Betts has lots to tell us about including a Venus transit that you did not, repeat, did not miss. There's still time for you to help us make Planetary Radio better. You'll find our easy, quick questionnaire at I'm very grateful to all of you who've already completed it and to those who are about to. We'll be shutting it down in a few days so we hope to hear from you very soon.

Mat Kaplan: There haven't been a lot of spectacular full-frame images of the International Space Station since space shuttles stopped visiting. This makes the lovely photo taken recently from a Crew Dragon spacecraft even more special. You'll find it at the top of the January 14 edition of the Downlink, where there's coverage of the trouble Perseverance has had with one of the samples it has attempted to collect, some pebbles got in the way of the mechanism. We just learned that the rover is simply the going to dump them and take another sample from the same rock, so no big deal? NASA has a new chief scientist and it may signal a re-energized focus on earth science and especially climate change.

Mat Kaplan: Katherine Calvin is an accomplished climate scientist. I hope we'll get to talk with her on Planetary Radio before long and I also hope to bring back her predecessor, longtime friend of the show, Jim green. As always you'll find much more at The Jet Propulsion Lab's, Ashwin Vasavada served for many years as Deputy Project Scientist for the Mars Science Laboratory. He stepped up to Project Scientist when John Grotzinger returned to teaching and research at Caltech. That was in 2015. As you'll hear, Curiosity is still going strong. On January 18th, too late to include the news in my conversation with Ashwin, we learned about the rover's detection of a carbon isotope that is consistent with life. There are possible non-biological explanations but this is one more step toward that ultimate goal.

Mat Kaplan: By the way, we've got a link to this story and many other great resources on this week's episode page at Ashwin, welcome back to Planetary Radio for this check-in on the Curiosity mission, the Mars Science Laboratory mission in your honor and the mission's honor, I'm wearing my Planet Fest Curiosity t-shirt, the one that says, "Curiosity knows no bounds," it's a nine and a half-year old t-shirt because, well, we just passed the 10th anniversary of Curiosity's launch last November and it will have been exploring Mars for 10 years this coming August. Absolutely amazing. Thanks for being here.

Ashwin Vasavada: Absolutely. It's wonderful to be here. Yeah, I still can't get over it myself that we're doing so well, almost 10 years into the surface mission. It's wonderful.

Mat Kaplan: And I bet you're thankful for that RTG on the rear end of the rover, right? You don't have to worry about dust and at least that's one thing you don't have to worry about as much.

Ashwin Vasavada: Yeah, it's true. And fortunately, it's always been this case where you don't have to worry about dust killing you immediately but you know you have this gradual slow death over the long term. And we thought actually that would catch up with us by now but fortunately, we found ways to be very efficient with the energy we use and we've maximized what we can do and extended the life of the mission even with the declining RTG.

Mat Kaplan: I am not surprised that that team has found ways to stretch energy budget and you're in the same boat, you're in good company, you got Voyager out there, still struggling along past the outer planets. What is the status of the rover overall, its cameras, its instruments?

Ashwin Vasavada: Doing quite well. One thing I always like to make sure our bosses at NASA headquarters understand is that we have 10 very highly-functioning instruments to this day, which again, I'm just very grateful for and never would've expected to be in such a good shape 10 years later. All of our instruments are functioning very well, a few minor capabilities have been lost. One thing that is probably most apparent is we've lost our ability to measure winds, but we have a meteorology suite that does a lot of things besides just winds so we're continuing to measure the weather in other ways. And from the rover perspective, I think the best way to describe it is that we've overcome a lot of different challenges.

Ashwin Vasavada: And fortunately, there hasn't been anything that's been so severe that it's really decreased our capability. We lost the ability to drill for over a year but as you know, man, what a great feat by the engineering team here to find a new way to drill, to overcome the loss of that motor. So, that's been the story. There's been little, well, sometimes more than little problems with things like a motor or with the wheels or with the memory card, chips on the rover, that sort of thing. But in every case, it hasn't been a fatal error obviously, and we've been able to find ways to work around them. So, the rover and its instruments are doing great.

Mat Kaplan: I love to start with that intersection of art and science and we got a good example of that. Not too long ago, there was this panoramic view of a Martian landscape that in one image captured both morning and evening on the Red Planet and we'll put it up on this week's episode page, Did you find that as stunning as so many of the rest of us did?

Ashwin Vasavada: Yeah. And it's just jaw-dropping and it was so unexpected for us to have that reaction, I think and for that to have worked so well, not only with our team, but with the entire world, we got so much great feedback on that. The story behind that as we were climbing up, we'd been climbing up this very tall mountain and we've crested a little local hill and looked back and saw we had this great view of the crater floor and it's a very clear time of year. So, I asked one of our engineering camera leads, his name is Doug Ellison, and you probably know him.

Mat Kaplan: I do know Doug, yes. Very happy member of the team.

Ashwin Vasavada: Exactly. Yeah. So, I asked Doug I said, "You take navigation pictures all the time but let's take a nice panorama looking backwards that is at the highest quality that the engineering cameras can do," because those are spectacular cameras but they never get to show off. Our navigation images are compressed like crazy for efficiency reasons. And so he said, "Sure, I'll take some pictures and by the way, I want to take two, one in the morning and one in the evening." I said, "Okay, whatever, I don't care, do it." But he didn't tell me why. And he had already formulated this idea of how that might look. And so, Doug gets the credit and really made a wonderful visualization.

Mat Kaplan: Yeah, move over Jim Bell, who I call the Ansel Adams of Mars. This is really that kind of a shot. It's also amazing to look at the two original shots where the lighting has changed because the sun has moved to the other side of the sky and that end, that wonderful colorization, they really are, as you said, jaw-dropping. So, where are you now? Obviously, still climbing Mount Sharp, right?

Ashwin Vasavada: Yeah, that's correct and we'll continue to climb 'til we can climb no more. Gale Crater in Mount sharp had been such a wonderful place for us to explore. We felt when the site was selected, that the advantage of going to a place like Mount Sharp is that you climb a large mountain with layers that change in their appearance and their composition and therefore, record a varying geologic history. And that it would be a gift that would keep on giving. And that's certainly been the case. Every year, we climb to a new level on Mount Sharp, we're in a different part of Mars ancient history and exploring a different environment.

Ashwin Vasavada: And the place we're at now is a very important point in the mission, we're at a transition between layers that have a lot of clay minerals and layers that have sulfate mineral, and we can get into the importance of that later, but that's where we're at. And it also corresponds to a change from relatively flat topography to a topography that's characterized by a lot of buttes and mesas and hills. So, the surroundings have just gotten very spectacular too as we've gotten into this local area.

Mat Kaplan: So, this area that you've just left behind, the so-called Murray Formation has special meaning for a lot of us at The Planetary Society and I'm sure for a lot of you at JPL as well, because named after our co-founder, the former JPL Director, Bruce Murray. What did that formation tell us about Mars, this so-called clay unit?

Ashwin Vasavada: Sure. These names really are hallowed ones in planetary science. Mount Sharp is named after Robert Sharp who worked alongside Bruce Murray at Caltech in the early days when planetary science didn't really have a name, it was just people coming from different fields and applying physics and geology and terrestrial fields, building cameras to strap onto these JPL spacecraft. Anyway, I could go on about that but yes, we named the package of geologic layers at the base of Mount Sharp, we call that the Murray Formation. We've been exploring that now for probably about seven of the nine years that we've been on site there at Gale crater. And so far, there hasn't been a reason for the geologists to say that we've left that Murray Formation, it's all been very similar and all been dominantly layers laid down in ancient lakes, which has been wonderful for our goal of trying to understand whether Mars ever was habitable.

Ashwin Vasavada: The fact that we have hundreds of meters of lake bed sediments all stacked up in this mountain means that Mars was habitable for a long time. But lately, we found that things have been changing in a fairly significant way. The lake bed sediments are disappearing and being replaced now by sediments that were laid down in more dynamic environments, maybe at the shores of lakes or within rivers. It's been so persistent now that looking back over the last year or so, the geologists on our team who take care of this mapping and classification have decided that the Murray Formation ended and now we're in what we're calling the Carolyn Shoemaker Formation.

Mat Kaplan: Oh, and I'm sure she would've been quite honored. Carolyn Shoemaker of course, great explorer and scientist in her own right and the widow of Eugene Shoemaker who was quite a pioneer. So, with the Murray Formation, the clay unit left behind and you're now in this transitional area and you're seeing a lot of these sulfates, which have become one of the features of the Martian surface that weren't expected, not that many years ago, I mean, Viking wasn't expecting them and yet it got in the way of some of those old Viking experiments but they tell us a lot don't they?

Ashwin Vasavada: We think they do. Having the benefit of these orbiter missions behind us, the Mars Reconnaissance Orbiter and the Mars Express European mission, they mapped the planet and discovered this rich meteorology over the surface. And as you said, one thing that they've seen are lots of sulfates and they tend to overlie the clay mineral deposits in many areas. This has caused people to wonder whether there was a planet-wide transition from an environment that formed clay minerals to one that formed sulfates, which probably would correspond to a wet environment going into a dry environment.

Ashwin Vasavada: We're the first mission that can really explore that transition up close and personal on the surface and figure out if it really does correspond to a climate change within Gale and extrapolating that to the rest of Mars. Maybe this is evidence for that big transition that we all think happened early on in Mars history when it went from this wet planet, maybe warm planet to the dry planet it is today.

Mat Kaplan: Isn't that one of these big questions that you're hoping to answer? I mean, not just how wet was Mars, but when did that transition take place in its long history?

Ashwin Vasavada: Yeah, when did it take place? And then the benefit of what we can do at the surface is really see the detail of it. Was it a gradual transition that occurred over millions of years? Did it by expectations, when you look at the terrestrial record of climate changes, it probably wasn't just a black and white change, it probably came and went a few times. Wet, dry, wet, dry and then finally dry, dry, dry. We'll be able to look at that level of detail about what's the nature of that climate change on Mars? When did it occur and how did it occur?

Mat Kaplan: So, as we look at your data, the data from MRO, the data that's now arriving from Perseverance, your sister rover up there in Jezero Crater, do we now know .... I mean, sure we found the water a long time ago, we know at least we found the evidence of the past water. Do we now know just how wet Mars was if you look back far enough?

Ashwin Vasavada: I think where the mystery is is how did the planet get in a state where it could be so wet? So, we are quite convinced now that Mars was very wet. I mean, there's lots of evidence for rivers that floated on Mars for extended periods of time, it wasn't just an ephemeral thing. In other words, we know that because as we see deltas that poured sediment into standing bodies of water like lakes and the size of these deltas and all the meandering of the streams that occurred give us a sense that things were happening for a long time. And then, you get to Gale Crater where we now have 300 plus meters thick of lake sediments, that tells you also that water was there for quite a long time and rivers were flowing, bringing sediment for a long time.

Ashwin Vasavada: Where the mystery seems to be now in the community is finding a way to explain how the atmosphere was able to retain the warmth necessary to have stable water on Mars for such a long time. The sun was fainter back in the early period of Mars history and Mars probably never had too thick of an atmosphere. So, you it didn't have a lot of chance for a really extreme greenhouse warming to keep it warm. That's one of the mysteries. We don't really have climate models yet for early Mars that are consistent with the geology that we see.

Mat Kaplan: I think before we're done, I'll come back to that topic of the other spacecraft that are exploring above and on the Red Planet. But I'll leave that for a little bit later. There's another video that I think we'll link to from this week's episode page, it was narrated by your Deputy Project Scientist, Abigail Fraeman. It's a tour of a panorama captured by Curiosity last summer. It seems to be right in line with what you're talking about, that's looking at how and when the climate changed on Mars. And once again, comes back to these chemical compounds called sulfates. Can you describe them a little bit more?

Ashwin Vasavada: Sure. Clay minerals form when water interacts with rock over a long period of time and actually alters the mineralogy of the basaltic minerals that Mars formed with and turns some of them into clays. These sulfates on the other hand, might form more salts that you might find when a lake dries up. So, one possibility is that the sulfates that we're going to find in the sulfate unit above us now are what's called evaporates, minerals that are left behind because they precipitate out of water that's evaporating. It also could be water that was precipitated when groundwater was flowing through rocks underground.

Ashwin Vasavada: But generally, you might associate these sulfates with a drying environment, less water available than what would've been around when the clay minerals formed. So, there's this kind of a wedding to drying that we expect to find. We don't know the exact nature of the sulfates yet, that's one of the things that we're hoping to find, how exactly did these sulfates form and did they form when the sediments were being laid down or did they form later as water was circulating through those sediments at a different time?

Mat Kaplan: I'll be a little bit parochial here and think of a couple of features we have here in Southern California. And I'm wondering if these are decent parallels to what we may be seeing on Mars. The Salton Sea, that closed off inland body of water that is terribly salty but also, and I forget what it's called but it's that part of Death valley, it's the lowest part of Death Valley and it has these insane, surreal formations that I am told are made of salts that you don't want to fall on, they're sharp and abrasive, but they are an amazing thing to see. Is this the kind of structure or composition that we may be talking about?

Ashwin Vasavada: It's a possibility that these could be these macroscopic salt crystals. I think you're talking about Badwater or the Devils Golf Course, places like that.

Mat Kaplan: Yes, that's it. Thank you.

Ashwin Vasavada: Yeah, that would be spectacular if we rolled around the corner and we saw features like that. And that would be very distinctive in terms of telling us how these things formed, that they really did form as minerals precipitated from drying pools of water, where the salinity increased increased and you form crystals and all that. We haven't found anything like that yet and it's possible that they could be what we find, but it also could be that the salts formed in less obvious ways, maybe just in the spaces between sand grains in the rock as cements formed within the rock. So, not as big thick layers of salt like in the places you described but more as cements within the rocks as groundwater circulated and precipitated the salts in those spaces between the grains.

Mat Kaplan: Sticking with these salts for a little bit longer, there was a story that I saw came out a few months ago, I think about these salts sulfates and how they may have in a sense, I think it was referred to as rewriting the history of the geology in that area because they may have changed the nature of the clay, which is also present.

Ashwin Vasavada: Sure. One thing that we've really been impressed with about Gale Crater is how much change has occurred after the sediments were initially laid down. You have a lake and the lake is depositing silt on the ground forming layers but then that lake goes away but we still have groundwater circulating underground. And that groundwater can do a lot of changes to what was originally deposited and that process is called diagenesis, it's a term that geologists used to describe changes that occurred later in the history after the original deposition. The issue with that is, you'd like to go to a place like Gale Crater and interpret how everything formed but these later changes through diagenesis can overwrite what you're seeing. The changes can be so profound, they can erase the original history.

Ashwin Vasavada: And so in some cases, they've erased our ability to actually see distinct layers, the kinds of sedimentary layers that tell us whether a river once flowed or whether a dune passed by, the diagenesis can change the texture of the rock so much that that history is erased. Another way that these changes can happen is chemically and this is the one that you're referring to, where we have the clay-bearing unit and then later in Mars history, more segments were piled on top of those clay-bearing rocks, including ones that have all the sulfates. And so, one hypothesis is that then groundwater, mixed in some of those precipitates from the sulfate unit and the water flowed down through fractures and got to the clay-bearing unit and started changing the rocks of the clay-bearing unit. So now, what we're seeing in the clay-bearing unit has been altered by the rocks that formed later above them.

Ashwin Vasavada: It makes it challenging to interpret what's going on when you have this secondary process that's been overriding everything. On the other hand, it makes the history quite fascinating to explore. And so, we have this area in the clay-bearing unit where there's a big standing ridge that we call the Vera Rubin Bridge and this deep trough where the clay minerals are. And you'd think by looking at a trough next to a big ridge that they must have very different rocks to form them. Why is one a ridge and why is one a valley that gets eroded downward? And it turns out that the rocks formed all the same way in lakes a long time ago but it's this action of later Vera diagenesis that hardened the ridge and kept the clay rocks quite soft.

Mat Kaplan: Wild speculation on my part here, absolutely non-geologist, but can this be in any way compared to the formation of the beautiful mesas we see across the Southwest of the United States, where somehow this big column of harder material is left in place where everything else has been washed or worn away?

Ashwin Vasavada: I think it can create that sort of thing but we see also in Gale Crater things that are probably even more directly analogous to what you're saying. So, even after the clays and the sulfates were laid down and then some period of time went by and Mount Sharp formed into the shape of a mountain, then later on, sand dunes came across and coated the surface with sand and that hardened into rock. So, you put this shielding on these soft sediments below of this hard sandstone.

Ashwin Vasavada: And then, that sandstone got eroded in places and left towers because now you have this little cap of hard sandstone covering up soft rock below it and the soft rock keeps eroding away, but wherever the little cap is left behind, you end up forming a little tower. And that's a lot of what happens in the Southwest and that's what happens in this wonderful place we drove through called the Murray Buttes.

Mat Kaplan: You know why I have a big smile is because what you're talking about is just more evidence that we've been getting for years and certainly Curiosity has added to it, that Mars is not going to be simple to figure out, it's a dynamic place with an incredibly rich history.

Ashwin Vasavada: Yeah, amen to that. That is what we've been learning. And the history is so diverse and any rock you're looking at, you can't just go to a place that's three and a half billion years old and immediately understand the history three and a half billion years ago, because a rock that is three and a half billion years old also has had everything happen to it in the last three and a half billion years since then. So, there's been a lot of geology, a lot of time that's affected that rock. So, you have to understand its whole history and man, piecing together the history of everything that's happened in Gale Crater has been so wonderfully rich, but also made it a very challenging problem.

Mat Kaplan: Ashwin Vasavada will be right back with more from Mars, including the Curiosity rover's confirmation that Mars itself may someday protect astronauts from radiation.

Casey Dreier: Hi again, it's Casey Dreier, the Chief Advocate here at The Planetary Society. Our 2022 Day of Action is set for March 8th. This is your chance to advocate on behalf of space science and exploration. If you've heard us talk about how effective and just personally rewarding our past Days of Action have been, this event is for you. Learn how to participate in this virtual online experience by visiting If you live in the United States, we'll book your congressional meetings for you and also provide you expert training so you can be the best advocate possible. If you live outside the US, you can still make your voice heard on March 8th. It all starts at Join us as we speak out for space.

Mat Kaplan: Even as these salts or sulfates are making your life a little more difficult as you try to understand that long history, I read quotes from you and your predecessor, John Grotzinger, about what they may have to say about the search for evidence of past life and how life might have been supported. So, what do you and John mean by that?

Ashwin Vasavada: Yeah, there's a positive and negative. The point you raised earlier is that sometimes these fluids that percolate down into fractures and then cause these diagenetic changes into lower layers can erase the kind of history that we're looking for. They can erase the clay minerals that we associate with lake beds and that tell us that there was a wet environment that could have maybe supported life at that time. Those clays are gone, we lose some of that evidence to understand the possibility for life. But on the other hand, when you get these fluids that have all these chemicals that they picked up from one environment and they transport those chemicals down to a different environment, that creates a lot of chemical diversity underground, which is the kind of thing that is associated with life, it provides energy for life.

Ashwin Vasavada: And that's one thing that John has really been impressing on all of us in the mission is that it's not just the lakes that we should be excited about, but all this groundwater circulating below and carrying chemicals from one place to another, it creates a great possibility of a biosphere underground that outlived the lakes possibly for hundreds of millions of years. Gale Crater was not only habitable when the lakes were there but probably for a long afterwards.

Mat Kaplan: And we have heard speculation before on this program about that possibility that life, once again, found a way perhaps on Mars and dug down where it could still find water and stuff to eat and maybe also was shielded from that horrible radiation up on the surface. What's it going to take to find out what may have been or my goodness, might still be down there?

Ashwin Vasavada: Well, Curiosity continues to explore the habitability. Our mission was to get to Mars, to figure out what kinds of environments existed in the ancient past and whether they were the kinds of environments that life could have thrived in. And I think we found more than we ever expected in the positive side of that column. And that was intended, Curiosity was intended to be the predecessor for missions like Perseverance and Mars Sample Return, all the missions that would follow, to go to these environments, these habitable environments and then explore for actual signatures of past life.

Ashwin Vasavada: Perseverance is doing that now in Jezero Crater, both with the instruments it has on board, but even more so by collecting samples for return to earth. We're excited that everything Curiosity was hoped to find we found and that has set the stage wonderfully for the next decade of bringing rocks back from Mars and really answering the question, whether those habitable environments actually supported living organisms.

Mat Kaplan: Always comes back to sample return, doesn't it?

Ashwin Vasavada: Yeah.

Mat Kaplan: Let's look up from the surface of Mars. I mentioned to you before we started recording that I had Mark Lemmon of the Space Science Institute on the show last June and we talked about some more pretty pictures that your spacecraft or your rover took there on Mars by looking up at the Martian sky and seeing clouds, really beautiful clouds overhead. In fact, you could even see the clouds passing by. We'll put a link to that past show up as well. And you talked about that meteorological package that Curiosity carries. How big a part of the mission is that and how is that portion going looking up at the sky?

Ashwin Vasavada: It's often probably overshadowed by the habitability work that we do. But we do have some pretty important objectives in terms of understanding the meteorology of Mars and the cycles of water and dust. All the good stuff that happens on Mars today, as opposed to three and a half billion years ago. And so, we have a very capable meteorology package on board and we also have cameras that, of course we use for geology all the time, but then we point upwards and take pictures of clouds and dust in the sky. We have some great results over the years of now observing more than four Mars annual cycles, Mars years, about twice an earth year so our nine years on Mars converts to about four years in Mars years.

Ashwin Vasavada: But as you say, one of the more dramatic things was just in the last year or two when we were taking some pictures at twilight, which we don't often do when we look up at the sky and all of a sudden there was all these beautiful clouds in the sky. We take lot of pictures of clouds over the mission during the day but this was after the sun had set so not exactly the time you'd go and look for clouds. But these are the special type of clouds called noctilucent clouds, very high altitude, where they're still lit by the sun even when the sun's gone down from the perspective of the rover. And so, they're very bright against the sky.

Ashwin Vasavada: Not only were they bright but they're colorful. As your listeners probably heard from Mark, these are the kind of clouds that are called not only noctilucent but they're luminescent, but they have these Mother of Pearl-type colors to them, pastel colors and that tells us a lot about how they form and what they're made out of. And we think they're very high altitude that the altitudes probably wouldn't where carbon dioxide would freeze and form the ice particles.

Mat Kaplan: So, those are probably carbon dioxide or dry ice particles?

Ashwin Vasavada: Mm-hmm (affirmative), which is fascinating because carbon dioxide is what Mars atmosphere is made out of. So, you have the actual atmosphere condensing a little bit up at 60 kilometers height or so.

Mat Kaplan: They are gorgeous pictures. So, this region that you were headed toward, I know it's been given a name that means a lot to you and the team. Could you say something about Rafael Navarro?

Ashwin Vasavada: Sure. Yeah. Rafael Navarro was a member of our SAM team, which is an instrument that is the one that does the processing analysis of the samples that we take from our drill. He came from a university in Mexico and just a wonderful, generous scientist who worked with the team the entire time Curiosity was on Mars and made a number of interesting discoveries using that SAM data. And he passed a year ago or so and we saw a really wonderful mountain that was the gateway to the upper regions on Mount Sharp. We had to cross in front of this mountain then go around it to get where we are now at the base of the sulfate unit. And so, we thought it was just very fitting to call that mountain the gateway to the rest of our exploration on Curiosity the Rafael Navarro Mountain.

Mat Kaplan: Another terrific tribute.

Ashwin Vasavada: Using the spectroscopy that was done by the orbiters previously, we can map out on Mount Sharp where the clay minerals are and where the sulfate minerals are. And we're in this region that's sort of no man's land in between the two, which means we're seeing lots of changes as you might expect. We saw this change from the Murray Formation to the Carolyn Shoemaker Formation. So in other words, a change from lakes to these more dynamic environments. And then now, we're seeing the clay minerals disappear, we've drilled a series of holes and we saw less clay each time. And so, the obvious question then is, are the sulfates appearing? And so far, we haven't found nearly as much as we thought we might.

Ashwin Vasavada: So, we've seen the clays disappear but we're still waiting for the sulfates to appear. And that's been an interesting mystery too. We found little hints of sulfates in some of the diagenetic features, these features that have formed later after the original deposition, little nodules, concretions, fractures filled with minerals, those seem to contain the sulfates. But we still expect that we're going to find a lot more higher up because the orbital data tells us that there should be hundreds of meters of thick of rocks enriched in sulfates.

Mat Kaplan: So, safe to say more surprises ahead.

Ashwin Vasavada: I think so, more surprises ahead, we also are going to be looking not only at the sulfate unit, but even the layer that formed after the sulfate unit, which is this sandstone layer that you and I were discussing earlier. And also debris that has come down maybe in rivers and streams from higher on Mount Sharp. There's a channel we're going to explore that's filled with boulders and other debris, which might give us a chance to see what the rocks are like from much higher up on the mountain that we may never get to. And not only that, but to actually explore what might have been once a very fast-flowing river or debris avalanche from higher up on the mountain. So, lots of exciting stuff ahead.

Mat Kaplan: I told you earlier that I would want to ask you about the company that Curiosity keeps both on Mars and above Mars. And some of them have come up already, Perseverance, of course. But I wonder if you want to see anything else about how Curiosity fits into this, what has become a pretty massive program of exploration and now an international program of exploration across Mars. I'm thinking of InSight and the Chinese lander and rover, Perseverance of course, but also maybe what's to come like ExoMars with its drill that's hopefully going to take us deeper than we've ever gone.

Ashwin Vasavada: It's wonderful that NASA has a Mars exploration strategy. And we talked about that briefly already that we have a very specific place, we being Curiosity, in this long series of missions that went from mapping Mars and looking for signs of water from orbit to then exploring on the surface with Spirit and Opportunity and then Curiosity, understanding habitability so not just water but habitability. And then, ultimately searching for actual signs of life with Perseverance and Sample Return. So, we're in that thread of the Mars program. But of course, Mars is a planet, there's so much else you want to learn about it. And so, it's exciting that there's missions like InSight where you can learn about the interior of Mars, which we can say very little about as a rover on the surface.

Ashwin Vasavada: We're excited that other nations, other space agencies are successfully landing at Mars like the Chinese rover and then other orbiters from India, from UAE. So many countries now are exploring Mars. It's a wonderful place and so much still to learn that I'm glad that we can do so many complimentary things. Sample Return is going to be a huge investment on behalf of NASA so it's nice that some of these things that are not going to be priorities for NASA's Sample Return thread are going to be picked up by some of these other missions and we'll continue to learn about some of the other aspects of Mars.

Mat Kaplan: So, a lot left to learn, a lot left to explore. As you know, the goal we've all been told is we keep focused on getting humans up there. And all of us at The Planetary Society, I think it's safe to say look forward to humans walking on the Red Planet. Those humans are going to have to be protected from radiation among other things. Is Curiosity helping us to prepare for that challenge? I read a little bit about this.

Ashwin Vasavada: Yes, it certainly is and we've had some exciting new results lately that are directly relevant to keeping humans safe on Mars one day. We have 10 instruments on the rover and one of them was support initially by the human exploration part of NASA. 10 years ago, they asked us to fly a radiation sensor so we can study the amount of high-energy radiation, the kind of radiation that for example, could cause cancer if you're not sufficiently shielded from it. So, it's very important for us to measure that at the surface because we've measured it in space before but Mars, not only in the good sense, shields a lot of that radiation just because now you have the planet below you and you're only exposed to half the radiation you get from space when it's coming at you from all directions.

Ashwin Vasavada: But also the opposite, the negative side is that that radiation can interact with the atmosphere of Mars or the rocks on Mars and cause what's called secondary particles that could be more harmful than the initial particles because they might be bigger or slower than those initial particles and more likely to cause changes in your body. We've been measuring that now for nine and a half years. One neat experiment we did recently was got up close to a cliff to figure out if we hunkered next to a cliff, like an astronaut might do some day, how much would that cliff shield us? And importantly, would it shield us or would those secondary particles increase instead and it would be more dangerous to hang out below that cliff?

Ashwin Vasavada: And we figured out that the size of this cliff and the thickness of it was sufficient to actually shield the rover from that radiation. And so, that's an important data point to think about in the future when we're designing habitats for astronauts.

Mat Kaplan: I'm also thinking about those little bits of material that could be used to make spacesuits for humans to wear on Mars that are on Perseverance. So, that arrow taking us toward that time when we see boots on Mars seems to be getting a little bit closer. I'm looking forward to the day when oh, human tourists or others, explorers, maybe go and visit Curiosity and put a little sign up next to it and salute it for what it did to teach us about this planet and also help prepare the way for them. And Ashwin, it's great to talk to you about that work that is underway. Thank you to you and the entire team. It is a great pleasure and we'll continue to follow the mission.

Ashwin Vasavada: Appreciate it very much. It's really exciting and we're just so glad to keep going.

Mat Kaplan: Time for What's Up on Planetary Radio. We are joined again by the Chief Scientist of The Planetary Society. He's Bruce Betts and I wish you could see him, he's doing the most interesting things with his beard, what's left of it anyway. Welcome.

Bruce Betts: They're mostly to amuse you, Mat since not many people see me and my kids.

Mat Kaplan: I wish I could share this picture and I bet your kids are quite entertained.

Bruce Betts: They're adults but I think they think it's a little ridiculous but funny, it's gradually going away.

Mat Kaplan: Hey Bruce, what's not going away?

Bruce Betts: Well, it's complicated but planets in general not going away but they are going in and out and around the sky. You know what that devious Venus did?

Mat Kaplan: What?

Bruce Betts: It crossed between us and the sun very quickly. And so, it went from being in the evening sky a couple weeks ago, now it's pretty much firmly placed in the morning sky in the pre-dawn east. Super bright Venus, still very low but pops up within the next week or two, you should be able to see it quite easily.

Mat Kaplan: So, if it went between us and the sun but there wasn't a transit? No transit of Venus across the surface?

Bruce Betts: It probably was and probably no one predicted it. No, there was not a transit, the two planets done an orbit in exactly the same plane and it's so far away and the sun is so far away, you really have to line it up pretty perfectly, which is why you only get a couple transits every whatever it is, 100 years-ish. It's like the moon, you don't get a total eclipse every time it passes between ... So anyway, look in the pre-dawn east and you got super bright Venus low on the horizon. Above it to its upper right is Mars so it'll get closer over the coming couple weeks. And above Mars, reddish Mars is the reddish star Antares. The evening sky Jupiter still holding out over in the west, looking super bright. And Saturn, not as bright, low by the horizon, you may see it, may not.

Bruce Betts: By the way, I've determined through scientific observation, we are fully in Northern hemisphere winter. So, I'm assuming Southern hemisphere summer. This of course, is marked by the easy viewing in the evening of the constellation Orion and so check out Orion rising in the east in the early evening and hanging out in the south after that. Sirius, brightest star in the sky, it's a party, it's a winter party or summer party.

Mat Kaplan: My fave, Orion.

Bruce Betts: Onto this week in space history. 1986, Voyager 2 flew past Uranus. Our one an only view so far of the Uranian system.

Mat Kaplan: Wow, yeah. And I guess, we should remind people that that's because the other Voyager spacecraft was diverted from Uranus to Neptune so that it could do that fly-by, wasn't it to get a good view of Saturn or the moons or something?

Bruce Betts: It was to get a good view of Titan. And so, they took Voyager 1 in order to get a good view of Titan and fly-by it, it took it out of the plane of the planets. And Voyager 2 did that grand tour, had that special alignment that allowed it to do four planets. And another cool spacecraft, groundcraft, Opportunity landed, the rover landed in 2004 this week.

Mat Kaplan: Wow.

Bruce Betts: And operated for like a gazillion years.

Mat Kaplan: It sure did.

Bruce Betts: We move on to Random Space Facts. Parker Solar Probe, you may have heard of that recently on, I don't know, this show. Not only has set records as the closest spacecraft to the sun, tied to that is sets records every time it goes flying closer to the sun for the fastest spacecraft ever relative to the sun. In its fastest planned periapse in a few years, it'll be 192 kilometers per second or 119 miles per second. You were probably wondering, Mat if it flew across the contiguous United States west to east from the Pacific to the Atlantic at that speed, how long would it take? Less than 24 seconds.

Mat Kaplan: Man, oh man. Much faster than anything in lower earth orbit, that's fascinating. Thank You.

Bruce Betts: All right. We'll move on to the trivia contest and we asked you about Fraunhofer or at least that's where we got to the answer. I asked you, who are the main solar absorption lines that visible wavelengths named for? So, you split the spectrum, the sun into a rainbow spectrum, you do it well enough you see a bunch of black lines tied to absorption features in the sun's atmosphere of different elements. Who was that guy that we named it after that I also just told you so it's not really a surprise? Mat, how'd we do?

Mat Kaplan: Well, Beau Garner and a whole bunch of other people did really well but it was Beau who got the nod from this week. I believe a first time winner in Virginia. Full name, well, actually not full name because he's got one of those German names that goes on and on and on. But Joseph von Fraunhofer was good enough for Beau to win this time around. Congratulations, Beau. We're going to send you, probably the last one going out I think, another one of those 2022 International Space Station wall calendars that we have at the office. So, we'll ask folks to put that in the mail to you very soon, Beau.

Mat Kaplan: Get this from Beau, he heard the show that I did. We reported on the preparation for the recovery of the Artemis 1 Orion capsule, "Loved hearing about the USS John P Murtha's potential recovery for the Artemis capsules, he just joined the Navy not too long ago." He says, "So now, I know where I should try to get stationed in order to claim my connection to our missions to the moon." Hey, we'll welcome you to San Diego, Beau and you know what I'm going to say, right? Thank you for your service.

Bruce Betts: Yes, thank you for your service and congratulations.

Mat Kaplan: From Mel Powell in California, he says, "I wondered why a great guy who can't pronounce Quadrantids would hit us with the answer Fraunhofer until I realized that only Mat has to pronounce it and Bruce just says that's correct. Well played, Dr. Betts."

Bruce Betts: That's correct. Yes, I screwed up in my-

Mat Kaplan: Yeah.

Bruce Betts: Yeah. Although, I find Fraunhofer much easier to say than that other thing.

Mat Kaplan: Laura Dodd in California said it was over 600 of those solar absorption lines in the visible spectrum that Joe, Joseph discovered.

Bruce Betts: Joey.

Mat Kaplan: Joey, Joey, Joey. We got this from a retired astronomer, Claude Plymate, who has been my guest on the show. He actually wrote quite a bit about Joseph. He says, "After a career in solar spectroscopy, I better be able to answer this question of von Fraunhofer invented the modern spectroscope using a slit and prism." And like I said, he said a whole bunch of other great stuff, we just don't have time to read. But he adds, "if George Ellery Hale is credited as the father of solar astrophysics, Fraunhofer should then at least be known as its grandfather."

Bruce Betts: Works for me.

Mat Kaplan: We also heard from Claude's wife and fellow solar astronomer, Teresa, she says they got to look through a telescope that Fraunhofer made during a visit to Germany.

Bruce Betts: Wow.

Mat Kaplan: Speaking of Germany, Thornsten Zimmer, "Named after Fraunhofer is the Fraunhofer Society for the Advancement of Applied Research, which has 75 institutes and about 29,000 employees," so they really honor the guy there. Carlos Perez also in Germany, there's a Fraunhofer Institute in Carlos' hometown of Erlangen and one of his best friends works there. Sadly, he came to a poor ending, did Joe, we're told by Michael Ungeren in British Columbia, died due to poisonous heavy metal gases or vapors. He liked to work with that stuff, measuring the spectra. Ungeren speculates that it might have been Iron Maiden, but he probably would've preferred Rainbow.

Bruce Betts: I was going to make a heavy metal joke but I thought it was in poor taste.

Mat Kaplan: Of course, it is.

Bruce Betts: But maybe too soon? The man passed away just almost 200 years ago, with all due respect.

Mat Kaplan: Here is an interesting bit of poetry from Jonathan Gorback in Virginia, he's a two-year listener. First time he's entered because he said he's been waiting for you to give him a contest where the answer is a proper noun of six syllables so that he could submit a double dactyl poem. I had to look it up, I'm sorry to say. It's a form of poetry invented in 1951. Here's the poem, "Higgledy-piggledy Joseph von Fraunhofer pointed a prism at heavenly orb. Thus, he invented the helio spectroscope, lines show the atoms, the sun's gases absorb."

Bruce Betts: Wow.

Mat Kaplan: You've been double dactylized.

Bruce Betts: I was double dactylized.

Mat Kaplan: We also got a really terrific poem from Gene Lewin in Washington but it's too long to read. Thank you, Gene though I enjoyed it. And we'll close with this one from Dave Fairchild. "Joseph von Fraunhofer noticed some dark over top of the sun spectra lines. Photosphere gases were blocking as light passes, dragging the photons behind. It was absorption and there was no option. The energy couldn't get by. The sun was committed but light had submitted, got sucked up by gas in the sky." It sounds a little like a Mother Goose rhyme. Aw.

Bruce Betts: A weird Mother Goose rhyme but a nice one.

Mat Kaplan: Man, that was a lot of stuff. And by the way, thank you to all of you who wished us a happy new year. The same to you folks as well. Here's Bruce with a new question.

Bruce Betts: What planets in our solar system have higher "surface" gravity than earth? For the giant planets, which have no surfaces, use the gravity of the one bar pressure level, which is about one atmosphere. Then go to Get us your entry.

Mat Kaplan: You've got until the 26th, that would be January 26th at 8:00 AM Pacific time to get us this answer and possibly win yourself a Planetary Society Kick Asteroid rubber asteroid. We're done.

Bruce Betts: All right everybody, go out there look up the night sky and think about, what should they think about, Mat?

Mat Kaplan: They should think about answering our survey while there's still time at Tell us what you think of Planetary Radio and Bruce getting totally lost in his thinking.

Bruce Betts: Thank you and goodnight, von Bettsinberg out.

Mat Kaplan: That's von Bettsinberg, he joins us every week here for What's Up. Sounded like we planned that survey mention, didn't it?

Bruce Betts: Nope.

Mat Kaplan: But that's not the fault of Associate Producers, Mark Hilverda and Jason Davis. Josh Doyle composed our theme, which is arranged and performed by Pieter Schlosser. Ad astra.