Planetary Radio • Jan 20, 2021

7 More Minutes of Terror: Perseverance Arrives at Mars

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Gregory Villar

Entry, Descent and Landing system engineer for NASA/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

The 2020 Mars Rover will reach the Red Planet on February 18th after many months in the relative quiet of space. It will then undergo a true trial by fire as it descends to the surface. Jet Propulsion Lab systems engineer Gregory Villar and his colleagues hope it will arrive as successfully as its sister Curiosity did in 2012. He tells host Mat Kaplan what to expect. Planetary Radio listeners prove once again that they are awesome as they go to amazing and unnecessary lengths (oops!) to answer the space trivia quiz.

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Perseverance Rover Landing Animation Animation depicting key events during entry, descent, and landing that will occur when NASA’s Perseverance rover lands on Mars February 18, 2021. In the span of about seven minutes, the spacecraft slows down from about 12,100 mph (19,500 kph) at the top of the Martian atmosphere to about 2 mph (3 kph) at touchdown in an area called Jezero Crater.

Perseverance Touches Down on Mars (Illustration)
Perseverance Touches Down on Mars (Illustration) An illustration of NASA's Perseverance rover landing safely on Mars.Image: JPL / NASA
Perseverance Rover's Entry, Descent and Landing Profile
Perseverance Rover's Entry, Descent and Landing Profile This illustration shows the events that occur in the final minutes of the nearly seven-month journey that NASA's Perseverance rover takes to Mars. Hundreds of critical events must execute perfectly and exactly on time for the rover to land on Mars safely.Image: NASA / JPL-Caltech

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Mat Kaplan: Looking forward to 7 More Minutes of Terror as Perseverance reaches Mars, this week on Planetary Radio. Welcome, I'm Mat Kaplan of The Planetary Society with more of the human adventure across our solar system and beyond. Gregory Villar is a young engineer who will join his JPL colleagues and the rest of the world as Perseverance, the Mars 2020 rover, plunges toward the Red Planet's surface on February 18th. He'll help us to understand that heroine event on today's show. By the way, you'll be able to join The Planetary Society celebration of Mars when we go online for Planetfest '21, beginning February 13th. Details are at

Mat Kaplan: "The time has come," the pod host said, "to talk of many things of solar sails and capped on film of misstatements and wings." Which is my way of teasing this week's What's Up visit with chief scientist, Bruce Betts. But before we get to any of this, let's visit the weekly newsletter from The Planetary Society. Headlines from the January 15 edition of the Downlink are led by something you heard Andrew Jones mentioned here a few weeks ago, China may send a lander to Jupiter's moon, Callisto, arriving there in 2035. It's one of two proposed missions by China to our solar system's giant world.

Mat Kaplan: We're also happy to report that Jupiter orbiter, Juno, and the InSight lander on Mars have been granted mission extensions by NASA. Juno will examine the other Galilean moons. And NASA finally held that static test of the space launch system's core stage. It looked great for about a minute before shutting down well short of the planned eight minutes. We've just learned that computers ended the test when a "intentionally conservative" pressure limit was reached in a hydraulic system. There was at least one other unexpected minor anomaly. Lastly, kudos to Virgin Galactic sister company, Virgin Orbit. It put 10 CubeSats up there with the first successful air launch by its LauncherOne system.

Mat Kaplan: Gregory Villar is an entry, descent and landing system engineer on the Mars 2020 rover mission. He has spent nearly eight years working toward what is about to happen on Mars. As you're about to hear, he got his start at the Jet Propulsion Lab several years earlier while he was just a college sophomore. Now he's a major contributor to what we hope will be another successful arrival at the Red Planet. Gregory, thanks so much for joining us on Planetary Radio.

Gregory Villar: Mat, thanks for having me. I'm so excited to be here today.

Mat Kaplan: I was thrilled that you were recommended as somebody to talk to because your expertise is in exactly the area that we had in mind, but you also have an interesting history there at JPL that has led you to this moment. As people hear this about one month out from what we're calling 7 More Minutes of Terror as Perseverance this time descends to the Martian surface. First of all, do I have that right? How much is this going to be like what we all experienced with such thrill when a Curiosity made it down to the surface several years ago?

Gregory Villar: You know, Mat, it's probably even more exciting in some way. This is basically the beginning of what we're calling the Mars Sample Return Campaign. As with any Mars landing, it's very challenging. Although we always see the successful landing on Mars, everything is still very challenging about it. In that regard, it will be very exciting. It will also be very nail-biting. So let's all hope for the best here.

Mat Kaplan: Most of us who listened to this show anyway, and certainly I, remember those thrilling moments, bone-chilling moments as Curiosity made its way down. We have seen the so-called landing ellipse, the area in which you expect the spacecraft to land, has been shrinking ever since we got into this game with Viking all those years ago. This is another leap in that direction, isn't it? you really are looking to make a pretty precise landing.

Gregory Villar: Yeah, that's very true, Mat. I'm glad you've done your homework here. But basically, between Curiosity and Perseverance, the landing architecture is mostly the same with some improvements here. And some of these improvements have been able to get us to reduce the size of our ellipse. One of which is this technology called range trigger. So basically, we are deploying our parachute based on our range to target, which helps us shrink in that ellipse. And also, the more popular thing, as probably people have heard about, is terrain-relative navigation, which is a really cool new technology we have on Perseverance landing.

Gregory Villar: Basically, the way that works is, when we release our heat shield, we have visibility to the ground with a camera, as we're on our parachute, we'll be taking images with this camera and correlating that with an onboard map we have. We will be able to better understand where we are at that point in time, and then with predetermined safe spots on the map we have on board, we will be able to be able to say, "Look, this is where we currently are, and here are all the safe places we can go to. So therefore, let's go to one of those dedicated safe spots." Those are two of the new things on the entry, descent and landing system that enables us to have a much smaller ellipse.

Mat Kaplan: I'm going to put up a link on this week show page at to a show that we did months and months ago, where I went to JPL, back when we could actually do that kind of thing, pre pandemic, and was in one of the labs there looking at some hardware, four tiny little radar dishes, only a few centimeters or inches across, which are going to be doing some of this work that you're talking about. I got to tell you, it was thrilling to be standing there looking at this hardware in front of me on a work bench.

Gregory Villar: That's one of the benefits of us being local to Pasadena, it's just being able to visit places like JPL; before, of course, the pandemic, and being able to see all of this really firsthand technology that is going to be at Mars at some point in the future. I think that's a very fortunate thing we have for us.

Mat Kaplan: You very kindly gave me a link to a page on the Perseverance site, and we will link to this page as well, of course, from the show site, the episode page, it is a diagram showing the descent of Perseverance, all the different steps. Why don't you take us through this? First of all, it does look remarkably like what Curiosity did.

Gregory Villar: Oh, absolutely. Just as scary, but just as exciting as Curiosity. So basically, this is what we call the entry, descent and landing phase of our mission. For short, we call it EDL, or as popularized back in Curiosity, The 7 Minutes of Terror. When we launched from Florida, this spacecraft has basically traveled over 300 million miles. And by the time it reaches Mars, it's going to be traveling really, really fast, on the order of like 12,000 miles per hour. Before we get to the atmosphere, we're actually attached to this thing called the cruise stage. You can think of the cruise stage as like our Uber driver. The rover is in the air shell capsule and this capsule is attached to the cruise stage, which is taking us to Mars through space.

Gregory Villar: So about 10 minutes before we get into the Martian atmosphere, we separate from our driver, this cruise stage, and this air shell that we're in, it maneuvers towards the right orientation that it's going to use to go through an EDL. And so the first thing that happens is we use our air shell and we break through the atmosphere. The analogy I like to use is, imagine you're driving in a car and you're going really, really fast on the highway, and you just let go of the gas. You don't even push the brake. You're slowing down because of air resistance. And that's basically the first part of EDL where we use the Martian atmosphere to slow down.

Gregory Villar: As we're slowing down, we're regenerating a lot of heat from the friction of going through the atmosphere. And that's why we have this heat shield protecting us and protecting the rover and everything else from burning up. And we're going through this atmosphere at close to 12 Gs. And then we enter a portion called entry guidance. This is the maneuver that the Apollo capsules use as they reentered her. But what happens here is we have an ideal of where we want to go, our target. So we have these little thrusters on the capsule that helps us maneuver through the atmosphere to get us to that point in time and space.

Gregory Villar: When we reach supersonic speeds, we deploy what's called a supersonic parachute, that gets us to down to about 900 miles per hour, but 900 miles an hour is still super fast. You wouldn't want touch the surface of Mars at 900 miles an hour. So the next thing we do is we release our heat shield. So when we release our heat shield, we now have visibility to the ground. So now there are two things we can do here to aid relative navigation, which I mentioned earlier, but also we are now able to use our landing radar, which we also had on Curiosity. And this landing radar helps us understand our velocity and our altitude.

Gregory Villar: When we're at a right velocity, altitude pair, that is our signal for us to separate from our dock shell pressure configuration and come down on these thrusters. So at this point we have our rover on what's called a descent stage, or as I like to refer it, as its own jet pack. And it's coming down on these thrusters. When it's about 60, 70 feet from the ground, the jet pack lowers the rover on these cables slowly. As it's coming down, the rover releases its wheels like a landing gear for an airplane. On the order of little less than a mile per hour, we hopefully softly touch down on the ground.

Gregory Villar: When that jet tech senses that the rover has softly touched the ground, we cut those cables and the jet pack, or the descent stage flies away from the rover, further away from where the rover is supposed to drive. Because we wouldn't want this jet pack to contaminate that site. And then we're on the surface of Mars.

Mat Kaplan: Makes it almost sound easy. You didn't use the term that so many of us came to know during that heroine landing of Curiosity, the Sky Crane, which is that rocket platform, that jet pack, that actually winches the rover down to the surface. That was the thing, I think, that you made so many of us lay people think, "Oh my God, is this nuts are, or is JPL as good as they usually are?"

Gregory Villar: That's funny, you mentioned that because early in the history of Curiosity, Sky Crane was very... People are very pessimistic about Sky Crane. There was years of design and proving it to an external review board and to NASA headquarters. It was like, "Come on, is this actually going to work?" So it took a lot of convincing to headquarters and our external review board that this would actually work. And it was just such an elegant solution for such a different problem compared to previous rovers, like Spirit and Opportunity and Pathfinder.

Mat Kaplan: It has to be something of a relief to know that this worked once before. And I assume you got lots of good data from that entry, descent and landing.

Gregory Villar: I would say yes and no. At the time, I believe I was, let's see, 2012, I was about two or three years into my JPL career and only one year of experience on the EDL team at the time. I just on the surface, knew that it was complicated. And so when we landed, I was like, "Oh, sweet. That was really awesome." But I've been working on this landing system now on Perseverance for the past seven and a half years. And I look back and think, "Wow, I did not know how complicated this actually was and how frightening this was." But I know that I'm confident in all the people that I've worked on this project with.

Gregory Villar: And everyone's so very smart, so very diligent. And we do our due diligence. Whether it's like on the testing or analysis, we're going to do everything we can up to the point where we can't do anything so that whatever happens on landing day, we will hopefully be sure that we did what we can do. It's still very, very nerve wracking, but I'm also very excited.

Mat Kaplan: Let me bring up another element that you mentioned, that parachute, that supersonic parachute, no small achievement in itself. Your colleague, he's now JPL's chief engineer, Rob Manning, has talked with us on this show several times. He is such fun to talk to about this because he seems to have been almost as entertained by the failures as this parachute was developed as by its success. This is no small feat.

Gregory Villar: No, absolutely not. In fact there were several... I think it was a very hot topic at the beginning of the Mars 2020 project. Between Curiosity and Perseverance, there was this other project called LDSD, the Low Density Supersonic Decelerator campaign. And basically, on one of their tests, one of their parachutes failed. And that really brought into question our understanding of parachutes, like, did we just get lucky on Curiosity? So that's one of years of just debate and testing, building a new parachute.

Gregory Villar: I was actually fortunate enough that part of my experience on Perseverance was to lead the parachute test campaign in the world's largest wind tunnel at the wind tunnel at NASA Ames. So that was really cool. We got to test some parachutes in there, and ultimately bringing that to our NASA Sounding Rocket Program called the SPIRE. It's another acronym. I could probably send you what that means, but basically we put our parachutes on these sounding rockets to test them at supersonic conditions as well. It was something that really put us into question and be like, "We need to open that book back up because parachutes are not an exact science here. So we have to do as much as best as we can in terms of analyzing and testing them." But it's also really, really cool.

Gregory Villar: With anything that's as interesting as that, people tend to really keep their focus and make sure that they're doing their due diligence.

Mat Kaplan: Not only did you have to get this parachute up to a really high rate of speed using the sounding rocket, wasn't part of this also, I hope I have this right. Obviously, if you're going to test a parachute and try to simulate the Martian atmosphere, there's a heck of a lot less of it than you're going to find that the surface of Earth. Was this also to get you up high in Earth's atmosphere where it was somewhat similar to Mars?

Gregory Villar: Very good. Yes. I love how educated you are. And that's exactly right.

Mat Kaplan: We're big fans. You've got to know that.

Gregory Villar: I do. I do. I would have been a big fan as well, and that's why I get to do what I do today. But you're right, there are a lot of things on the EDL system that basically cannot be tested end to end because earth is not Mars. So we basically have to do these testing in pieces, and a piece of this is parachute testing. And you're correct, the deployment altitude that we chose for the sounding rockets was to somewhat mimic the atmosphere conditions on Mars, as much as possible. Of course, it's not going to be exactly the same on Mars, but because the atmosphere of Mars is less than earth, we have to go higher up into earth atmosphere to get somewhat comparable environments.

Mat Kaplan: Of my conversation with Perseverance rover engineer, Gregory Villar is coming up after this break.

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Mat Kaplan: You have this complicated sequence, and I really do hope that people will go and take a look at this diagram, that traces this 7 Minutes of Terror. Remind us, how much control will you folks at JPL have over this process as Perseverance descends?

Gregory Villar: That's a very good question, and I see a very interesting question for those who don't know. In the diagram that you see, basically from this point on, there is zero human control. We do a lot of preparation before this diagram that you see even hours or days before, but all of this that you see on the diagram is completely automated. So we're just going to be hoping that all of our testing that we've done on the spacecraft will be able to come to fruition and it's up to the spacecraft and its sensors and its algorithms and everything to land safely on its own.

Mat Kaplan: And again, it has to be somewhat reassuring, the Curiosity managed to do this just right as did in slightly different fashion, Spirit, Opportunity and earlier spacecraft. But still, the fact that you basically are during this time, just spectators like the rest of us, it has to add to that atmosphere of nail biting.

Gregory Villar: Oh, absolutely. I need to share a story that we had on Curiosity. I think most people who would probably watched the Curiosity landing remember someone, his name is Al Chen. He's basically our lead EDL person right now in Perseverance, but he was a person narrating Curiosity landing. And the notable moment was when Al Chen said, "Touchdown confirmed." And then everyone starts celebrating. What most people don't know actually is there's a backstory here, which I like to share in my talks.

Gregory Villar: There are actually three indicators that we have internally that you can actually hear it on the net, but people really didn't know what we were saying. We don't want to just say touchdown confirmed without really being sure that that's the case. And we'll do something similar for Perseverance. But basically those call signs where one, tangled, Delta nominal, which basically means we received signal from the rover that it sends that it touched the ground. The next one, you could probably hear it said, "Remy's stable." And that meant basically we have an IMU, an Additional Measurement Unit, which measures if something is moving.

Gregory Villar: You can imagine the rover touching down, but maybe it's sliding or maybe it's rolling. If it's sliding or rolling, we're like, “Well, that was not a safe landing." So when we say Remy's stable, we're basically saying the rover is just steady, it's not moving. And then the third indication was, "Calm was still good," or something like that. The reason we had that was because you can imagine that the rover touches down, it's stable, but this jet pack or the sky crane smashes on the rover, it just doesn't communicate anymore.

Gregory Villar: So we want to wait a certain period of time to confirm like, yes, the sensation flew away and we're still getting signals coming from that rover. And so in Curiosity, the EDL team, we knew these three indicators coming along, but they told us do not react, do not react until you hear Al Chen say, “Touchdown confirmed." It's funny when you see some of us in the video, when we hear some of these indicators, we're basically holding back our excitement as much as we can, because to us, we are ready to just jump up with joy.

Gregory Villar: It was boiling up by the time Al said touchdown confirmed, and it really amplified the celebration at that point.

Mat Kaplan: That is absolutely fascinating, and I probably should have been aware of these extra samples, but yeah, of course, my God, God forbid you should land on the side of a cliff. The one, and I hesitate to bring it up, but maybe bringing it up we'll help make sure it doesn't happen, the one that scared me so badly about Curiosity was not getting down to the surface, but I had this morbid paranoid fear that one of the pyros would not fire. They would separate the cables from Perseverance and let the sky crane fly off to the side and crash as it did. Pyros are pretty well-proven technology, right?

Gregory Villar: Yes, they are. That's also a fair concern for a lot of us. There's 70-plus pyros through this whole EDL sequence. We don't just use the pyros to cut the cables, all the way from the beginning of separating from the crew stage, there are pyros there. There are pyros involved with deploying the parachute, there are pyros involved with separating the heat shield, there are pyros involved for separating the 10 stage from the back shell, there are pyros everywhere. Although the pyros are very reliable technology, another way we mitigate that is by we fire two signals instead of pyros.

Gregory Villar: So as long as one of these signals get to this pyros, hopefully that will ignite and that will be enough to ignite it and fulfill its function for that purpose of the sequence.

Mat Kaplan: All right, Gregory. Thanks a lot. Now, I have to try not to be 70 times as worried with the landing. That's all right, I'm sure it's all in hand. We're down on the surface, what happens? Obviously, the celebration takes place, and I will be part of that, you can count on that. What happens in those first few minutes after Perseverance is safely on the surface?

Gregory Villar: We touch down safely, hopefully softly, that's the plan. Whenever you're new to an environment, whether it's getting off a plane in a different country, or maybe imagine yourself being on the moon one day, you have to orient yourself, things doesn't just happen right away. So in the first few seconds or minutes, basically one of the first things we do is, we take some pictures with what are called Hazcams or hazard cameras. Those also get sent to earth so that we can... Another means of confirming that we touched down safely.

Gregory Villar: And then we'll continue to get information from the rover and do things like activate our antennas for communication and just give time for the rover to assess itself and produce all the data it needs or data that it needs to send to us so we can assess it on the coming communication passes we get from the orbiters around Mars. Also, not just in the next few seconds or minutes, but in the first few days, we're doing a bunch of things like getting this data from the rover and just assessing the health power systems, the thermal systems, all those things to make sure that we have a healthy rover.

Gregory Villar: We're not going to rush through it, but also we'll be very efficient about just understanding how that rover's doing on Mars before doing any major activities. I would say the first major activity is what's called a software transition. From launch to the journey to Mars, through entry, descent, and landing, there's one major software suite that's on the rover that really fulfilled its purpose for that journey, but once we get to the surface of Mars, that's completely different set of expertise that's needed, so we have to switch out our operating system, and that activity takes place in a little over a week after week we land on Mars.

Mat Kaplan: That's another big moment, I'm sure, almost like not a new operating system, but are all new apps, is that a fair analogy?

Gregory Villar: I like the way that... Yeah, that's a great analogy actually. Not just an operating system, but also apps. For example, one app is driving. The rover doesn't really need to drive while it's in its spaceship in space. So we'll have to do that and things for most of the instruments, you could say, they're like a toned down version of these instrument apps during the cruise phase of the mission, but now we need to use their full capabilities. That's great. I'm going to start using that, new operating system in US.

Mat Kaplan: When does the mast get raised? And we get those beautiful Mastcam-Z images will start to come back to earth.

Gregory Villar: Depending how things go, I'm not quite sure when the mast gets raised, but I would imagine it's in the first week or so if all goes well. I believe the drive, again, if all things go well as planned, within the first two weeks. So hopefully by that point, we will need the mast obviously to the drivers as well. So I would say around two to three weeks, just to be conservative here.

Mat Kaplan: Through all of this, it has been up to you and your fellow engineers, the other men and women who designed, built and got Perseverance to Mars, but through all of this, you've had that other key group involved with this mission, the scientists, who have been egging you on and waiting for you to finish your work so that they can start to learn about this exciting portion of Mars that we've never been to before, Jezero crater. Do you have much interaction with the science team?

Gregory Villar: We do for specific things, two things that come to mind, maybe more relevant for the general audience. There's this whole process called the landing site selection, over the course of the project, we've had landing site workshops. And part of these workshops is to assess where to go. Ultimately, we obviously decided on going to Jezero crater, but that required a balance of engineering assessment and scientific interest. So part of the EDL team's job is to say, “Hey, are these planning sites safe to go to, or are we capable of going to these landing sites?"

Gregory Villar: So in that regard, yes, we do interact with a scientist, but more so, feeding into that process, I run this group called the Council of Atmospheres, which sounds pretty fine, like the Council of Elrond, I guess, but basically, this group are a group of atmospheric scientist and a group of EDL engineers, whose job it is to characterize the marshal environment during the timeframe of EDL, because understanding the environment feeds into our physical simulations of EDL.

Gregory Villar: And so we need to feed that into those and to understand what the challenges we will have if any, with the marshaling environment. So yes and no, we do have to interact with scientists for specific things, for entry, descent, and landing, but I would say the bulk of the science interaction is with the surface team, the service engineers. I know this from my experience on Curiosity, where I was able to work for, I believe the first 200 sols, which was also a completely different and amazing experience working on Mars time.

Mat Kaplan: I won't ask you which group, the engineers or the scientists are the Elvis or the Hobbits, but that's fascinating. And I'd forgotten, of course, that engineers were a key part of that decision about where to go, which of these landing sites are you satisfied from the engineering standpoint that Jezero is not just very scientifically promising, but a safe place for Perseverance to explore.

Gregory Villar: Absolutely. The way this landing systems progress through history is in the beginning, it was really just the engineering that drove the selection of the landing site, It's just like, “Well, let's just go to somewhere safe, somewhere flat, like a landing strip, so there's no hazards or anything." Part of this makes me throw it out a little bit because compared to past landing sites, Jezero is a little more challenging in terms of hazards and terrain and all that, but we have that technology now. That's the cool thing about innovation and technology development is we're now able to utilize these things that we've developed on earth to be able to go to more exciting places on Mars.

Gregory Villar: So I am happy because it's a cool thing to be able to say, “Look, we're using this technology to be able to go to these cooler places on Mars." And that's something that wasn't possible before.

Mat Kaplan: What wonderful progress. I wonder if you think of yourself now, now that you've been there for over 12 years as an old timer at JPL, in spite of the fact that, when you got your start, you were still an undergrad at Cal Poly Pomona, part of the California State University system.

Gregory Villar: That's right. I was very, very fortunate. It's an interesting path I took here, but basically, when I was an undergrad at Cal Poly, I was majoring in physics and I was sophomore. I was a sophomore in physics, and my advisor approached me and a classmate saying, “Hey, one of my old students is now doing a postdoc at JPL, do you guys want to help him?" And I didn't really know what I was getting into, but fortunately, it was looking for brown dwarfs using the Palomar Observatory.

Gregory Villar: At the time, I didn't know what I was getting into, but I was like, "Sure, this sounds like good experience. What's JPL, whatever? I don't know what that is, but sure." And it all started with me going to Palomar Observatory. I still remember driving up at nights, and the sky was so clear, the moon was a little bit bright, but when we got into the dome of the Palomar Observatory, I remember being inside a dome, pitch black, and just like, "Where am I?" All of a sudden I hear this humming sound, which were the motors to open up the dome.

Gregory Villar: Slowly, this humming sound keeps going, and I see the sliver of the domes slightly open up, and seconds later, the moonlight just illuminates the entire dome. And I see this huge 200 inch telescope, I'm hooked. So that was a really quite fortunate experience where basically I was able to attach my name to a paper and apply to a NASA scholarship. And that NASA scholarship came with an internship at a NASA center of my choice. It was really cool because I was a baby at the time and I didn't want to leave LA, so I just chose JPL because it was in LA, but I ended up loving it.

Gregory Villar: So I interned there for two years and I eventually turned that internship into a job. And one of my first jobs was fortunately being able to work on Curiosity.

Mat Kaplan: And you spent some time on Cassini as well, not too long, but got a little exposure to that mission?

Gregory Villar: Yeah. That's also a super cool mission. People talk a lot about Mars, but Cassini was such an amazing feat. Hopefully, most people saw the culmination a few years ago, but the way that worked was between Curiosity and Perseverance, I had a little downtime, and so I was looking around JPL to see what else people needed help with. And there was a group, they were the Radio Science Operation group. So I believe I spent about a year or so helping the Radio Science Operation group do their observations with the Cassini spacecraft.

Gregory Villar: We would look at observations from the radio instruments and how they're interacting with Saturn's atmosphere. And so that was really cool experience as well, because it's a different mission aside from something on Mars,

Mat Kaplan: You have picked up quite a spectrum of experience across your time. Well, beginning, I suppose, at Palomar, but extending right through today.

Gregory Villar: I feel very fortunate. I think it was the ideal of just like taking initiative and really realizing that there's so much that JPL has to offer. To be honest, when I was an intern for two years, I basically was only interacting with my mentor and the students who are also assigned to my mentor. And embarrassingly, when I started in 2008, I didn't really know about Mars missions, I know Phoenix was landing at the time, but I was like, "What is this Phoenix thing? Oh, okay. Whatever." And it wasn't until I was actually employed in 2010 where I'm like, "Wow, they're like flight projects at JPL."

Gregory Villar: One of the cool things about working there, it's just the diversity of experiences you could get there.

Mat Kaplan: What do you say to, because I know you do this, you do some outreach work, what do you say to undergraduates who maybe are intrigued, inspired by your career and others and would like to follow in your footsteps?

Gregory Villar: That's a very common question that I get, I guess there are a lot of pieces of advice that I give. I think in the context of interns, I believe the best advice is finding something that you like and networking appropriately. People tend to chase a certain goal or ambition, but I think if you just find something that you actually love doing, that is a much better way to go because, I say this, but over the past 12 years, I go to work, but for the most part, it really doesn't feel like I'm going to work, if you know what I mean.

Gregory Villar: And another big thing is, as I mentioned, my first two years at JPL was in that little cubicle basically, and not interacting with the rest of JPL. And so another piece of advice I give is, just get out there. Once you're in a system, in this case, JPL, explore your surroundings, talk to other people, use the resources that you have, where you are now. So at JPL, on my breaks, if I was interested in, for example, black holes, I would find a black hole expert at JPL and ask that person if they would want to grab coffee. Or if I heard about Mars landings, I would try to find someone who's willing to talk to me over lunch about Mars flight projects.

Gregory Villar: So things like that, just really focus on your goal, but also don't forget to explore your surroundings as well.

Mat Kaplan: Excellent advice. And who would have thought, not you, I bet, from sound of it, that you would start out helping to learn about brown dwarf stars and end up helping us get back to Mars.

Gregory Villar: If you asked me at the time when I was studying brown dwarfs if I would be involved in what I am today, I would definitely have not seen that coming.

Mat Kaplan: I have a recommendation for you as somebody who worked in that field, a book called Cosmic Odyssey. It's about the work that has taken place at Palomar for decades by Linda Schweizer, an astronomer, we're going to have her on the show before too long. It is a wonderful, wonderful book about all of the knowledge of our solar system and the universe that we have gained from the Palomar Observatory, which is a very special place to me as well, really kind of a shrine of science. I love going there, and I can understand how it got you started with the role in NASA and all this. It covers the work that you were doing on brown dwarfs as well.

Gregory Villar: Oh, Awesome.

Mat Kaplan: That's a chapter in the book. So a little preview for the rest of you out there. Gregory, I'll leave you with this, where will you be on February 18th during those seven minutes of terror?

Gregory Villar: I will be with the rest of my colleagues specifically at JPL in what's called the EDL War Room. It will be a bittersweet considering that we're in the COVID era here, but we've been working on this, I've been working on this for the past seven and a half years, and I don't think there's any other place I'd want to be then with the people who've also done just as much work or more than I have. So that's where I'll be on 90 day.

Mat Kaplan: Gregory. I wish you and the entire team and all of us, the greatest of success with this next arrival on Mars. The Perseverance rover coming down in Jezero on, as we said, February 18th. Best of luck,

Gregory Villar: Mat, thank you so much for having me. I really enjoyed this interview.

Mat Kaplan: Me too. JPL, entry, descent, and landing systems engineer, Gregory Villar. Bruce Betts joins us next.

Mat Kaplan: It's time for What's Up on Planetary Radio. We are joined by the chief scientist of the Planetary Society. Bruce Betts is here to tell us about the night sky and resolve some confusion that I cause with the quiz question that you put out there two weeks ago. We'll get to that. Welcome.

Bruce Betts: Thank you. Looking forward to it.

Mat Kaplan: Yeah. Well, distract me. What's Up?

Bruce Betts: What's Up? Well, I've also gotten rid of several planets in the last week or two.

Mat Kaplan: So good. It was clogging up the system.

Bruce Betts: It really was. You won't be able to see Saturn, you probably can't see Jupiter, Venus they're respectively in the sun setting and sun rising glare. You can however, see Mars, and I brought in an extra planet just to help out. So Mars in the evening sky, high in the South, looking reddish, pretty bright, and near Mars for the next, a little bit, Uranus. Uranus which is from most sites, not visible with just your eyes unless you have really good eyes from really dark site.

Bruce Betts: But with binoculars, you can see it as a blue dot, with a telescope, you may even be able to resolve it as a little bit of a disk. Well, Mars is clipping through the sky, so what you're going to want to do for Uranus is take out a finder chart from the internet. It's tricky to find, because it's Uranus, but it's near Mars, so it gives you a nice spot in the sky to look forward in the evening sky.

Mat Kaplan: That's very cool. I always like it when Uranus comes back into view and you tell us that, if you've got great eyesight and really dark skies, you might not need any assistance to pick it out. That's a something for a bucket list, I guess.

Bruce Betts: Great eyesight?

Mat Kaplan: Great hearing would be even better for me.

Bruce Betts: We'll put that on the bucket list. We move on to this week in space history in 1986, Voyager two flew past Uranus. Speaking of which, got a much better view than you will in the night sky, but only a brief view whereas you get to see it frequently if you look for it. 2004, opportunity landed successfully on the Red Planet and did some Mars rover for many, many years.

Mat Kaplan: Going on 17 years ago. Just amazing. It is 17 years ago, that makes me feel elderly.

Bruce Betts: The older we get, the more I think we should use Mars years, possibly even Jupiter years, maybe Saturn. I'm not quite the Saturn years yet, like 30 year, earth years.

Mat Kaplan: We need an app for that.

Bruce Betts: I'm sure there probably is one. Let us move on to Random Space Fact.

Mat Kaplan: You know you don't have to fake the echo, I add it for you.

Bruce Betts: Oh, well then, Random Space Fact. The surface area of Ganymede Jupiter's moon, which you may recall is the solar system's largest known, its surface area is bigger than the combined surface areas of Asia, Europe and Africa. It's a lot of surface area.

Mat Kaplan: You're talking about combined, right? Those three combined.

Bruce Betts: Those three continents combined, still not quite as large as what we have to explore, that is the surface area of Ganymede. Remember, Titan's not that much smaller, so you can think of a Titans about those three continents worth as well.

Mat Kaplan: Lots more to see out there.

Bruce Betts: We move on to the trivia contest. Oh, the trivia contest. I asked you, what is the approximate mass of NEA Scout, Near-Earth Asteroid Scout? Matt, what did you ask those people who weren't listening carefully to the radio show, but going to our website, which are not the people ironically who are listening to our radio show right now?

Mat Kaplan: The NEA [COPA 00:39:31] that you heard Bruce's emphasis on the first person singular there, that's because he got it right. I added extra words when I put it on the webpage, I asked, what is the approximate mass of the NEA Scout solar sail? And a whole bunch of you resourceful geeks out there decided that what we probably wanted was the mass of just the sail, which was not the case. But my gosh, did a bunch of you do a great job, we can't go through all of these, but we got answers from everybody who calculated it because nobody found it online anywhere.

Mat Kaplan: They ranged from an estimate of 22.9 grams up to about a kilogram. They centered though around the low 300s, the low 300 grams, like Hudson Ansley in New Jersey, he said like 325 grams, assuming the density of the film was about one and a half grams per cubic centimeter. Andy Lupin in California went a little bit further, he said, “I calculated the mass from the manufacturer's data sheet."

Bruce Betts: Nice.

Mat Kaplan: And so he took the area of the sail, two and a half microns by 1.54 grams per centimeter equals 331 grams plus... Anyway, it goes on from there. And then he figured in the aluminum coating as well.

Bruce Betts: This is great to the people did this. I'm so sorry, I hope you found it edifying experience. So we will accept either in terms of what chooses is the winner. I don't know the actual answer, I'd say, these are probably giving us pretty close to the actual answer.

Mat Kaplan: It's a preponderance, at that range, Pablo Kamisha also came up with about 300 grams, but he added if the sail were made of graphene and one Adam thick, the sail would weigh about a quarter of a kilogram less. In other words, the sail would only be about 50 grams.

Bruce Betts: A little harder to get a hold of one Adam thick graphene so far, but we look forward to the future.

Mat Kaplan: Yeah. Won't that be great? Enough fooling around. The winner, and he's the first time winner, is Brett Krueger in Kansas with 14 kilograms or about 31 pounds if you want those Imperial units, first time entering the contest. Hope I'm right. Enjoy listening each week. Welcome, Brett, we're very glad to have you on board. And now, you've not only won, but we're going to be sending you a copy of Stellaris: People of the Stars edited by Hampson and the guy who's the principal investigator for NEA- Scout, Les Johnson. So congratulations, Brett.

Bruce Betts: Congratulations. Well, that was exciting. You got any more?

Mat Kaplan: I got two more funny ones here, from perennial favorite, Mel Powell in California. He says, "14 kilograms, a bit less than my favorite object, the Stanley Cup, which comes in at 15 and a half kilograms, but I've never seen an NHL hockey player skate a lap while lifting a cube set over his head yet." And finally, one we can all agree on from Thomas Ancillary in New York, "Woo. Solar sailing, gnarly my dudes." All right, we can move on.

Bruce Betts: We shall move on to this trivia question. We talked about Ganymede and of course, there are three other so-called Galilean moons of Jupiter, Galilean satellites, Io, Europa, Ganymede, and Callisto. What did Galileo who discovered them, what did Galileo want to name them after? Hint, it's not what they ended up being named. Go to

Mat Kaplan: It doesn't happen all the time, but I know this one.

Bruce Betts: Yes. I need to do a new one. You enter the contest legally like everyone else.

Mat Kaplan: I hope I win. You've got until Wednesday, January 27th, that'd be Wednesday, the 27th at 8:00 AM Pacific Time. And if you win, we will award you a Planetary Radio t-shirt that you can see being modeled at or just go to And you can check out all the march from the society. I apologize.

Bruce Betts: Yours was a really good question and showed our audience is capable of advanced calculations. So now I can really let my mind wander more.

Mat Kaplan: Look what I've created. Say goodnight, Bruce.

Bruce Betts: Good night, Bruce. All right, everybody, go out there, look at the night sky and think about what you would name four moons. Thank you. And good night.

Mat Kaplan: I'm going to get one out of the way right now so that none of you can do this really obvious one: Groucho, Chico, Harpo, and Zippo, and Gummo would have been there if there was a fifth moon, but Gummo dropped out of the act, so the heck with him.

Bruce Betts: Maybe we'll find a small moon to name after Gummo.

Mat Kaplan: Planetary Radio is produced by the Planetary Society in Pasadena, California, and it's made possible by its very smart members. Learn how to join them at Mark Hilverda is our associate producer. Josh Doyle composed our theme, which is arranged and performed by Peter Schlosser. Ad astra.