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Jeffrey Plaut

Jeffrey Plaut

Mars Odyssey Project Scientist, MARSIS Co-PI, RIME Co-PI

By David Zierler, Director of the Caltech Heritage Project

September 29, 2023

DAVID ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It is Friday, September 29, 2023. It is great to be here with Dr. Jeffrey Plaut of JPL. Jeff, it's so nice to be with you. Thank you for joining me today.

JEFFREY PLAUT: It's my pleasure.

ZIERLER: To start, would you please tell me your titles and affiliations at JPL?

PLAUT: Yes, I am a Senior Research Scientist and Project Scientist at JPL.

ZIERLER: There are so many missions that we're going to talk about, but do the terms Senior Research Scientist and/or Project Scientist attach to particular missions? Or are those your titles regardless of whatever particular project you're working on?

PLAUT: Project Scientist is attached to particular missions, yes. Senior Research Scientist is a category of researchers at JPL, scientists and engineers both, that are recognized by the Lab as sort of the scientific leaders of the Lab. The criteria are meant to be equivalent to a full professorship at a major university. There are between 100 and 150 Senior Research Scientists who have gotten this recognition at JPL. That's a general kind of term.

ZIERLER: Is it sort of like a minister without portfolio, or are you a senior research scientist within a particular directorate or group?

PLAUT: That designation doesn't carry any particular association with your organization. But I am in an organization, I'm in the Planetary Science area of the Science Division, and there's even a smaller group that I'm a part of, which is Planetary Geophysics. I'm also the Project Scientist on a Mars project, which is the 2001 Mars Odyssey Orbiter project. That's one of my assignments that's not directly tied to the research that I do as an independent researcher at JPL.

ZIERLER: Are there any other ongoing missions that you're part of?

PLAUT: Yes, I seem to always be involved in multiple missions. For me, that's a very fortunate circumstance because it means that there are exciting things always happening, and also I don't have to always feel the pressure of hunting around for additional funding. I'm involved in two other Mars missions, both orbiters. Mars Reconnaissance Orbiter, which is a JPL mission, and Mars Express, which is a European Space Agency mission. Then, I'm involved in another ESA mission called JUICE, Jupiter Icy Moons Explorer. That mission just recently launched towards Jupiter. And finally, I'm part of the Europa Clipper mission. A lot of different planetary missions. In every case, they are spacecraft that either orbit or fly by their targets, not landers or rovers.

ZIERLER: I wonder what any given day looks like, given all of your involvement in these missions. Do you tend to compartmentalize, where you're able to focus on one mission on a given day? Or is it really a jumble depending on what's going on?

PLAUT: Oh, it's quite a jumble. These missions have cycles and phases of activity and downtime. But I also like to squeeze in research as well, since that's sort of the bread and butter of a JPL scientist, the research that they do. All the project work is sort of to help pay the bills in some ways. However, I should say that many of the missions I'm involved in are not at the project level but at the science instrument level, and those become research tasks then. When an instrument that you're a team member of actually starts acquiring data during its investigation, then you really can put your scientist hat on and analyze the new data as they come down. And that's the case for a number of these missions. The one mission where I'm really doing a project role is 2001 Mars Odyssey, where I'm the Project Scientist.

ZIERLER: For your research, is it always tied to one of the missions or projects? Or are you interested in or capable of writing papers that might not be directly related to these projects?

PLAUT: I'd like to think I'm capable, and I certainly am interested in other things. But for the most part, over the last 15 years or so, almost all of my research has been related to the spacecraft instruments that I've been involved with. We'll get into this further during the discussion, but almost all of them have to do with radar remote sensing. That's sort of my specialty niche.

ZIERLER: What about administrative responsibilities? Are you managing or mentoring people, particularly in your role as project scientist?

PLAUT: A JPL project scientist is charged with the responsibility to oversee the science on a project and to ensure that the scientific goals of the project are met. That's a very broad, wide statement of what a project scientist does. When you get down to the week-by-week or day-by-day activity, it does involve managing a team, and it's usually the science team of your project. Those are co-investigators or the principal investigators of the instruments that might be on your spacecraft. In general, they're not JPL scientists, although sometimes they are. They're usually at other institutions, colleges, universities, other centers, other research facilities. There is a certain amount of management involved in that. A project scientist will usually have a deputy and maybe some other people on the staff, depending on the size of the mission, so you would directly supervise or manage those people. In some cases, mentor. Often, a deputy project scientist will be an earlier-career person, and you can sort of have that protege-mentor relationship. And then, along the way, I've had some excellent opportunities to mentor students, whether they're graduate students or summer interns, etc.

ZIERLER: On that point, I'm always curious about the connections, the way that Caltech and JPL are assets for each other. For you, whether it's collaborations with faculty or mentoring students, coming down to campus, if there's ever a reason, how does Caltech serve as an asset for all of the things that you do?

PLAUT: Well, I have served on doctoral thesis committees for Caltech graduate students. I've been asked to serve on some of those committees because either I'm collaborating with the student directly, or their advisor feels they need some expertise, so they turn to people at JPL to help with that dissertation committee role. And I have had several post-docs who came out of Caltech. That's a common pipeline. Also, graduate students while they're doing their graduate work often come to JPL to collaborate if there's an opportunity that maybe they can't quite get on campus. From time to time, I've had the chance to do those kinds of collaborations. It's not a constant thing, it kind of comes and goes.

ZIERLER: Between your educational trajectory, all the things that you work on, maybe even at a cocktail party, what do you tell people that you do? Planetary physicist? Planetary geoscientist? What's the go-to term for you?

PLAUT: I would start by saying planetary scientist. And for folks who don't really know exactly what that might be, I'll say, "You know, like Carl Sagan." [Laugh] That's the broad category that I might put myself into in a conversation like that. But more specifically, I consider myself a planetary geologist. My training is in geology, and then even more specifically in geologic remote sensing, using instruments aboard spacecraft or aircraft to learn about the geology or surface of a planet from a distance. That's remote sensing.

ZIERLER: For all of this work, have you ever been involved in terrestrial research? Or have you seen some of your research get put to use for Earth science?

PLAUT: Yes. I was fortunate to go to graduate school under the tutelage of an advisor who really felt that it was important for planetary scientists to have real-life terrestrial geological experience in the field. And a major element in my PhD thesis was field studies of surfaces that are analogs to planetary surfaces, where we were using instruments onboard aircraft to make measurements similar to what would be used on spacecraft at a planet. I had field sites in the Mojave Desert over volcanic terrains, desert terrains, sand dunes, alluvial fan features, and we had JPL instruments flying onboard aircraft over these sites as part of larger campaigns. But my thesis work, a big part of it was using this ground-truth or planetary analog approach to understanding how remote sensing works and what you could learn at a planetary target where you did not have the ground truth, all you had was the remote data.

ZIERLER: What have been some of the game-changing technologies that you've seen over the course of your career? What are you capable of doing now that might not have been possible or even conceivable maybe when you were a graduate student?

PLAUT: Interestingly enough, I would say the major technological advances had sort of just occurred when I was a graduate student, which was 25 or so years ago. And this was the revolution in both digital imaging and also in other kinds of remote-sensing techniques where we made the transition from analog to digital products. When you did that, it allowed you to become more quantitative about the things you were measuring. Because in a digital product, each measurement or each pixel is a number. You have a quantity that ultimately you'd like to turn from an electrical measurement at your sensor into some geophysical parameter. And when I was a grad student, that whole sort of paradigm shift or development in the field of remote sensing was just happening. Since then, things have just kind of been polishing up that new paradigm. We've come a long way in the area of radar remote sensing, which is kind of my special area. The computing and the clever ways the signal processing is accomplished have made some huge advances. I was at the beginning of the new era, and now we're well into that new era.

ZIERLER: What have been some of the major discoveries in planetary geology that you have been a part of? What has been most exciting on the discovery side for you?

PLAUT: Ranking them in order of excitement or impact, I would start with the studies of ice on Mars. The radar instruments, called radar sounders or sometimes ground-penetrating radar, in our case, they're onboard satellites orbiting Mars. The main task for these radar sounders is to probe beneath the surface of the target to see things that you couldn't see with any kind of visible or infrared technique. And in the case of Mars, we were able to see through and to the base of the polar ice caps of Mars, and that was a first, so it was very exciting to be part of that. And in doing so, we could measure the total amount of ice in the polar caps, put some constraints on the composition of that polar ice, learn about the internal layers and the climate history that might be recorded in the ice, similar to an ice core you might do in Antarctica or Greenland. It was, I think, quite significant that these instruments I participated in from the beginning eventually bore fruit and were able to penetrate all the way through the ice caps of Mars to their base.

And then, alongside that is a similar set of features on Mars that are not at the poles, but they contain a significant amount of ice. These are features that, from image data, appear similar to mountain glaciers on Earth. There was always a big question since the time of the Viking orbiters when these were first studied with image data whether they were in fact glaciers. If so, were they pure ice, mixtures of rock and ice, mostly rock with maybe a little bit of ice? We were able to use our radar systems to measure the composition to demonstrate they were almost pure ice, and in some cases, up to a kilometer thick masses of pure ice. And not in the poles of Mars, but in the mid-latitudes, so in the temperate latitudes of Mars. There were remnant glaciers from different climate eras. This, someday, will be a hugely significant discovery, once humans are able to access this ice. But in the meantime, it's quite tantalizing to think that there are huge masses of ice in the comfortable zones of latitudes of Mars that could be accessible to human explorers.

ZIERLER: That gets me to my next question. From Mars all the way out to the icy worlds, how do you see your research contributing to this all-important question of the search for life in our solar system?

PLAUT: Since our favorite target is ice, and often, that's water ice, you just need to warm that ice up a bit and maybe sprinkle some salt on it, and it becomes liquid water. And that, of course, is the key to the search for life, at least life as we know it on the Earth. Just about everywhere on Earth, where there is water, there's also life. Any place that even hints at the current, recent, or at some point in the past, presence of liquid water on a planetary surface, that immediately becomes an intriguing candidate for searching for evidence of life, whether it's extant life or remnants or biomarkers of life that may have existed in the past. A lot of the work that I do is sort of one step away from that question of the presence of liquid water, and therefore, a habitable environment.

For example, on Mars, we're still trying to sort out some intriguing echoes we received from the radar instruments at the base of the south polar cap, which some of our colleagues have interpreted as being present-day liquid water under the ice of the south polar cap. That immediately becomes a possibly habitable environment. Of course, in Europa, not too long from now, we're going to be flying some of these radar instruments over the surface of Europa, searching for the possible presence of liquid water somewhere near the surface. We know that there's an ocean deep below the ice of Europa, but there are lots of indications that water has percolated much closer and may have actually made its way to the surface from time to time. That also becomes another place in the solar system where we're thinking about habitable environments.

ZIERLER: For all of the Mars research that you've been involved with, how does it work in concert with or in a mutually beneficial way with the rover programs on Mars?

PLAUT: Well, there are two parts of that I've been involved in. Very different parts, actually. [I want to make sure I am able to mention this. For example, on the Mars Odyssey project, where I'm the project scientist, while we primarily do remote sensing from orbit, another role that the Mars orbiters play is communications relay platforms for the landers and rovers on the surface. The spacecraft that are in orbit are built with large solar panels and large radio dishes, powerful transmitters and receivers, so they have the capability to communicate with the Earth at a much faster rate, they can move data much more easily than a small lander or rover could do directly to the Earth. Almost all of the data that we have seen from the surface of Mars from a rover, lander, or helicopter has made its way back to the Earth through one of the orbiting satellites, including Mars Odyssey.

There's an intimate link. They're totally connected, the orbiters and the landers, for this sort of logistical, technical reason, just to move the data back and forth. That means that every day, usually twice a day, the orbiter will fly over a particular landing spot and communicate either sending commands, or more importantly, moving the data back from the lander to Earth. It also gives us the opportunity to make observations every time we fly by. The orbiters play a huge role in laying the foundation for where the next landing might be, determining whether it's safe, finding the scientifically interesting aspects of a landing site. There's a lot of synergy between the orbiters and the landers, not only for the communications, but also for the science.

ZIERLER: Are you involved at all in planning for Mars Sample Return? And will that change your interest or the science that you do with regard to Mars?

PLAUT: I am not directly involved in the Mars Sample Return program. We are hoping, although it seems rather unlikely now, that the 2001 Mars Odyssey Orbiter, which as you can tell by the name, was launched in 2001, will still be operating in time to support the Mars Sample Return activity. We do support the collection activity going on now with the Perseverance Rover, but again, that's a kind of logistical support, not really scientific support. I'm sort of just another bystander in the science community watching what's unfolding with Mars Sample Return. I find it really fascinating, the site that Perseverance is exploring and the huge variety of rocks that they've already been able to collect, sample, and study. It shall be a huge accomplishment for humanity if and when we get those samples back. I'm a big supporter of retrieving those samples, and it's technologically difficult, but there are no technological barriers to doing it. You've just got to spend enough resources to make sure you succeed.

ZIERLER: Moving out to the icy moons, thinking about this in concert with your work studying ice on Mars, what are some of the big similarities and differences between ice science on Mars and the icy moons?

PLAUT: Well, the targets are different beasts. Mars is a rocky planet, and the icy moons are icy bodies. Doesn't mean they don't have rock, and they do, but let's look at Europa first. It has an outer shell of 90-plus percent H2O, and it's a thick shell. Probably a hundred kilometers thick. That amount of H2O is more water than is contained in the Earth's oceans, certainly more water than is contained on Mars, in the subsurface of Mars or in the ice near the surface. The icy moons are, in a sense, at least on the outside, water worlds, whereas Mars is a rocky world that has a bit of ice here and there. That's a big difference. And the configuration of the ice and how it got to its current configuration are quite different in those two environments. Mars is similar enough to the Earth that it can be familiar to us how ice moves from place to place, basically through weather and the atmosphere. The atmosphere becomes the conduit for water vapor and condensation, whether it's rainfall or snowfall, evaporation, and the result of that is, when ice collects on Mars, it comes from above, and it collects in nice, organized, horizontal layers.

If you look at the radar images that we've collected over the polar caps of Mars, quite a prominent feature of the interiors of the Mars polar caps is that they're very well-organized layers, fine layers that probably represent cycles of climate and differences in the amount of dust, water, and perhaps sometimes CO2 ice that get deposited. In any case, you wind up with stratigraphy that is analogous to rock stratigraphy on the Earth, sedimentary stratigraphy, where the older stuff is on the bottom, it builds up in a nice, organized pile, and you can decipher the history by going through layer by layer, like you're reading pages from a book, which is how you'll often hear geologists describe the layers of rock. They tell a story that way. Now, when you go to an icy moon, the atmosphere's not really a factor in depositing layers. How does the ice get there? It's interacting with the liquid water from below. You've got sort of an upside-down case of how the ice gets distributed ultimately all the way up to the surface.

We're trying to anticipate what we will see when our radar reaches Europa in terms of the layering in the interior. And many of the folks on our radar team don't expect to see layering. There may be layering right at the surface, where there are some processes that work from above, such as meteorite or micro-meteorite impacts, that kind of gardening. That might create a sort of regolith or soil at the surface, so there might be a layer there. And there's definitely a thermal boundary at the surface. It's extremely cold at the surface of these planets, so you might have some thermal processes that create some layering near the surface. But once you get into the interior, you're dealing with sort of ice tectonics and thermal buoyancy when you have different materials, different ices, or liquid plumes moving up and down. We imagine the interior organization of Europa might be rather disorganized, whereas the interior organization of the ice on Mars is very well-organized.

ZIERLER: I'll ask a science-adjacent question because it'll be premised on a hunch, not on evidence. But in your gut, are you more bullish that in our lifetimes, we'll see evidence of either current or past life on Mars or the icy worlds? If it would happen anywhere in our solar system, where do you think it would happen first?

PLAUT: I'm a little biased, but my answer is Mars.

ZIERLER: Why would you say biased?

PLAUT: Just because I've sort of lived on Mars for the last 20 years or so. I think I understand it maybe a little better than I do the icy moons. I think it's a bit of an ask to get life started and supported continuously deep inside an icy moon at the distant parts of our solar system.

ZIERLER: Just because it's so cold?

PLAUT: Yeah, there's the temperature, but of course, if it's liquid water, that's warm enough. That's not really an issue. But the places where there's liquid water on Europa, for example, are quite removed from the surface. Whereas at Mars, we have evidence water flowed right across the surface. There may be liquid water at fairly shallow depths in places on Mars today. And then, another factor is this trading of materials that happens in the inner solar system. It's well-known that we have meteorites on the surface of the Earth that came from Mars, and all indications are the process works in the other direction as well. This sort of cross-fertilization of materials through impacts between Mars and the Earth could work in both directions.

In my mind, chances are there have been biological materials involved in that transfer. Again, it's a bit of a bias, and maybe it's also an Earth bias that Mars looks like a place where life might've had a good opportunity. Life as we understand life on the Earth. And maybe it was three or four billion years ago, but that was about the time life was getting started on the Earth as well. These processes have had plenty of time to act. That's sort of my hunch. I get the question a lot, "Is there life on Mars? What do you think the chances are?" And I'm still kind of 50/50 there. I think there's just as good a chance that we will find evidence that life has been or still is on Mars, I think at about a 50% level.

ZIERLER: Because Europa Clipper is coming up next year, what is it like being part of a mission where we're getting closer and closer to launch day, and what are some of your responsibilities to help make that happen?

PLAUT: I should point out that there are these parallel missions that the European Space Agency and NASA are doing to Jupiter to study the icy moons. Clipper is coming up to launch in about one year, which would be fall of 2024. JUICE has already launched in April of this year. When I began working on these projects and the instruments that were going to fly, I thought, "This is so far in the future, it's difficult to envision the thing actually happening." But JUICE is happening. [Laugh] JUICE has launched. We've turned on our radar, we're trying to understand how it works, how it interacts with the environment onboard the spacecraft. In about a year, it will do its first gravity-assist fly-by, flying by the Earth-Moon system, and it will fly close enough to the Moon to make some observations.

And we're hoping to turn on the radar to get some echoes off the surface of the Moon to see how the radar actually works with a target. We're deep into the operations phase of that radar experiment on the JUICE mission, and we're getting very close on Clipper. I need to tell you the names of these instruments. They are RIME, Radar for Icy Moon Exploration on JUICE, and then there's also REASON. REASON is flying on Clipper, a somewhat convoluted acronym, Radar for Europa Assessment and Sounding: Ocean to Near-surface. The team had to really kind of brute force that acronym to get RIME and REASON to be sisters, and use the Shakespearean phrase.

ZIERLER: What are the science objectives for REASON, and how does that fit in overall with the science objectives for Clipper?

PLAUT: We like to think that REASON is THE instrument on Clipper. [Laugh] But then, probably the other instruments' people would tell you that for their instrument. But the reason we think REASON is the key is that the whole point of Europa exploration is tied to it being a water world. Our instrument's ability to see through ice and detect water means it is going to be the only instrument that will basically touch the water. That is really at the heart of what Clipper is all about. They define it in their science objectives as determining the thickness of the ice layer. Everyone knows that underneath the ice layer is liquid water, so really what you're talking about is the depth to the liquid water. In particular, people are excited and interested to see if there are places where that water is close to the surface, and our radar would be able to discover and map those places, someday perhaps giving an opportunity for a lander with some kind of probe or drill to actually access the liquid bodies.

ZIERLER: I'm curious, either with JUICE or Clipper, long term, do you see these missions ultimately paving the way for a landing mission, even a way to get below the surface and have a submersible go into the liquid water?

PLAUT: There's a lot of work in that area going on currently at JPL and elsewhere. Folks are certainly thinking in those terms. It's an incredibly difficult, challenging task, but some very clever approaches are pretty far along in the study and development. Probably the most promising way to do it is to have a probe that heats the ice and melts it, and as it does so, it burrows into the ice while maintaining communications somehow with the surface, and ultimately breaks through that ice layer into a body of water, whether it's a perched lake or the ocean of Europa. It's definitely on the list for future exploration and pretty high priority, actually, at JPL, studying ways to go from the surface of Europa, as well as Enceladus, the moon of Jupiter, which also seems to have liquid in its interior, into the liquid in the subsurface.

ZIERLER: Let's go back now and establish some personal history. Let's start with your undergrad. Were you always on the planetary science and geophysics/geology side of things?

PLAUT: No. I was quite distant from that side of things. As an undergraduate, my major was in liberal arts in music. And I had some excellent professors, mentors, teachers in music as an undergrad, and I was very excited about the world of music at the time. I'm quite happy that I was able to get a bachelor's degree in music. At the same time, I had maintained an interest in math and science from a very young age, basically from early elementary school, and I carried that interest all the way through college. While I was doing my music major, I was also doing science, math, astronomy. As a senior undergraduate, I was at Brown University and enrolled in a class with a professor named James Head. I had also been reading Carl Sagan's books and been to some lectures by some other prominent planetary scientists, but that course really kind of lit the fuse in my mind that planetary science was something that maybe someday I would pursue.

ZIERLER: As a music major, what was your instrument?

PLAUT: I've studied piano since I was a child, so I would say piano and other keyboards. At the time, I was very interested in electronic music, and synthesizer music was just kind of becoming widespread, people could actually have access to synthesizers and very, very early digital synthesizers were just showing up right around 1980 or so. But I dabbled in a few other things. I was composing music for dance, working with choreographers, doing original pieces. I managed to learn some Indonesian orchestral instruments, something called a gamelan, if that rings a bell. Literally rings a bell, because there's a lot of banging on metal in gamelan instruments, both Javanese and Balinese gamelan. I tried a whole bunch of different things in music. I still play piano to this day, jam with friends, work out pop tunes, sometimes try to go back to my classical pieces. People often talk about the connections between music and science, and many books have been written on this topic. But I think there are analogies in, say, a tidy, elegant Bach invention or fugue and maybe a mathematical derivation or proof. There's an elegance that they have in common. I don't think it's a huge leap to go from one to the other, and you'll find that in geology in particular, there are a lot of musicians. A lot of people take their guitars into the field, sit around the campfire, and jam. [Laugh] It's not such a distant kind of connection to make.

ZIERLER: From that senior class as an undergraduate, did you pivot immediately to geology and planetary science? Did you pursue either a career option or graduate school right out of undergrad from there?

PLAUT: No, it took some time for me to close that loop. At the time, my family was living in Washington DC, so I graduated, came back home, signed up for the PACE Exam, which was the way that you show you're qualified for a government job. Being in Washington DC, it seemed like maybe I could find some work with the federal government. But the year was 1980, and just before Ronald Reagan defeated Jimmy Carter in November, the entire federal government put on a hiring freeze. There were no federal government jobs. [Laugh] I wound up finding a job, I got very lucky, actually, at a corporate law firm on K Street in Washington DC. K Street is kind of the lawyer/lobbyist mecca of DC. For four or five years, I worked in that area, mostly so I had money so I could travel to ultimate frisbee tournaments, of which I was a very serious player at the time.

ZIERLER: When does graduate school become a reality for you? When do you start to think about pursuing this in earnest?

PLAUT: Well, it sort of crept up on me as I was in that other world. The people in the law firms would say, "Oh, you're going to go to law school then, right?" And I said, "No, that's not really for me." "Well, then what are you going to do?" And then, it was like, "Hm, yeah, what am I going to do?" That experience that I had at Brown being introduced to planetary science really stuck with me, so I started picking up some other coursework in evening school. At the community college, or at some federal departments that offered undergraduate credits. I started sort of putting together a portfolio. "If I'm a music major, and I want to go study planetary science, how can I make myself a candidate?" I did that, and eventually, I got word of the program at Washington University in St. Louis where I wound up going to graduate school. I kind of elbowed my way in the door there and said, "I want to come here and be a graduate student." They said, "Well, were you a science major?" "No. But I'm really motivated, I really want to do this."

And I think I demonstrated that by the extra coursework I'd put in. I just kind of sold myself. It took an extra year. The first year, they said, "I think you may be qualified, but we don't have enough slots. Come back next year." And the next year, they had a number of scholarships available for the graduate program, and I started then. I basically had to complete the geology undergraduate program in that same department, the Department of Earth and Planetary Sciences, in my first year and a half or so. I loved it. It was extremely exciting, fascinating to me, a way of thinking about our planet that I hadn't really thought of before, and being able to extend that to the other planets of the solar system, it was just a great combination. And I owe a huge debt of gratitude to my advisor there, Professor Raymond Arvidson. He was the link to NASA and JPL that eventually led me to come to Pasadena.

ZIERLER: Tell me about Arvidson's work. What was he known for?

PLAUT: He was known primarily as a Mars guy. When he was a graduate student, and I think maybe a post-doc, he worked on the Viking project on both the Viking Lander and Viking Orbiter missions. And at a fairly early stage in his career, he got a position on the faculty at Washington University. At Wash U, as we call it, they have a long history of fundamental physics. Arthur Holly Compton was a Wash U person. They sort of branched that out into extraterrestrial materials, meteorite studies. They got some state-of-the-art facilities for analyzing samples from meteorites and lunar samples. And eventually, they decided, "We should add planetary science to our geology department." Ray was one of the first people in that new branch that they had started to develop where they were going to roll planetary geology into the existing geology department.

And at the time I was a graduate student, Ray was looking forward to two new missions that were coming up. One was called Mars Observer, an orbiter mission that JPL was managing, and the other was eventually called Magellan, which was the Venus radar mapping mission. At one point, after I had been in grad school for a year or two, Ray came up to me, and he had scribbled on the back of an envelope his timeline of these two missions. He said, "We're going to start working here, we're going to launch here, we're going to get to the planet here. Here's the one for Mars, here's the one for Venus. You could do either one of these. Which do you want to do? I think you should do Venus." I did Venus. Because Magellan was a radar, which is required for Venus, that sort of got me started as a radar remote-sensing geologist.

ZIERLER: Have you returned to Venus more recently? Or that was sort of isolated to your graduate experience?

PLAUT: No, that was my foot in the door at JPL. Just as I was completing my thesis, Magellan had arrived at Venus and had started collecting data. It was in the prime of its mission. And there was a need for extra scientists on the staff to support the project scientist, who was Steve Saunders. And I came on as a post-doc, working in that project science office, for Magellan. That was such a thrill and a treat, to be working on a mission that was just starting to return data from a very mysterious world. We had only gotten a few hints of what the surface of Venus looked like in some earlier radar data from the ground, from Pioneer Venus, and from a Soviet mission. But Magellan was a huge step forward in the amount of detail, and it did map the entire globe of Venus to understand the Earth's evil twin, as we call Venus, the hellish landscape that is sort of the mirror image but not, of Earth. I felt very lucky, even blessed, to just kind of be plopped into that whole exciting exploration that Magellan turned out to be.

ZIERLER: What aspects of your thesis research were really relevant for the post-doc on Magellan, and what was brand new for you and everyone else, given the timing of the mission?

PLAUT: I was in a bit of a sprint. I wanted to finish my thesis before Magellan started returning data because I thought, "Oh, now, I'm going to have to analyze Magellan data, and my thesis will become a Magellan thesis, and it'll take me two or three more years." The bulk of the data in my thesis was terrestrial data, as I described earlier, from our field sites in Death Valley and the Mojave Desert, where we had field data, measurements on the ground, and remote-sensing data. I also did analyze some Venus data that was acquired by JPL using the Deep Space Network.

The DSN antennas, in particular at Goldstone out in the Mojave, can also be used as radar antennas, and they are. Several solar system targets are actually pretty amenable to Earth-based radar observations with large dishes, and the Arecibo dish in Puerto Rico was the gold standard. They did the most remarkable radar imaging of Venus. But Goldstone also did some radar imaging, and I worked with the folks here at JPL who were involved in the Goldstone solar system imaging of Venus. That was also part of my thesis. There was a JPL scientist named Raymond Jurgens, who was the main person leading that. Both as a graduate student and a little bit as a post-doc when I got to JPL, I worked with them on the Goldstone Venus data.

We had data of Venus, we had data of terrestrial sites that sort of looked like Venus, like volcanic terrains and desert terrains, and I attempted, in my thesis, to connect those things and say, "On the Earth, we understand what's happening on the ground, what the materials are, what the processes are that cause those materials to be the way they are, and we have the remote-sensing radar data from the aircraft flying over. What can the radar tell us about the surface if we didn't have a lander or field work at the surface? What could we learn about the surface of Venus?" I think it helped a lot, actually, in understanding what the Magellan data were all about. Venus is primarily a volcanic world, so a lot of the work that we did on the volcanic terrains, particularly lava flows and volcanic edifices. A lot of the work that we did on the Earth, prepping for Magellan, really helped us understand what we were seeing on Venus with Magellan.

There's a particular class of volcanoes on Venus that came to be called pancake domes. They're sort of circular, well, pancakes. To me, they look more like maybe jelly donuts. But in any case, they're some kind of breakfast food landforms. But they're very similar to what on Earth we call silicic domes or obsidian domes. And in the Long Valley area, up by Mammoth Mountain, there's a whole series of these silica-rich lava domes, and I spent many weeks doing field work there to try to understand whether the Earth's silicic domes are good analogs to Venus's pancake domes. Turned out that in some ways, they are, but in some ways, they are not. The first-order intuitive interpretation of these on Venus being silica-rich didn't really quite pan out the way a lot of people were expecting.

ZIERLER: I'm curious, coming to JPL in 1991, right at the end of the Cold War, obviously you didn't have anything to compare it to, but were people talking about the post-Cold War budgetary crunch?

PLAUT: That era, for me, wasn't so much about the budgets, but it was actually about our interactions with the Soviets and then the Russians. I'm not really addressing your question, but it reminds me of some interesting things that were going on at the time. Before the fall of the Soviet Union, this professor who was quite an inspiration to me, Jim Head at Brown, was also basically singlehandedly developing a direct relationship with the Soviet planetary science community. And over, I'm sure, many objections of Washington, of the State Department. But he felt like there was a lot of mutual benefit for the scientists in the US and the Soviet Union, and across the world, in working together with them on planetary exploration. And at the time, Venus was very prominent in the Soviet program. They had the Venera landers, something with NASA never did, land on the surface of Venus and collect data. And they had orbiters, including radar orbiters, which kind of set the stage for Magellan.

A lot of this was happening while I was in graduate school, and I was associated with those folks because Jim Head was on our Magellan science team. I was able to participate in a lot of these bilateral meetings with the Soviet scientists and their graduate students and other workers. That was a very exciting and interesting time. Following that, we continued to work with the Russians. And on the Mars Odyssey project, which I'm still working on, we have a Russian instrument, and it's still working now 22 years later, the High-Energy Neutron Detector. That collaboration is difficult these days with the US-Russia relationship, but over the years, we had some very fruitful collaborations, and I was able to travel to Moscow several times, hold meetings there, give seminars. It's been an interesting history, how the geopolitics and the science kind of interact, the swings back and forth, where, "We want to swing the doors wide open," to, "Oh, now we have to close those doors again." The scientists kind of get caught in the middle of that.

ZIERLER: What was the opportunity that allowed you to transition from postdoc to staff at JPL?

PLAUT: That is a big challenge. It was back then, and it's probably even a more difficult challenge now. When recent graduates come to JPL as post-docs, they are told, "Don't expect to be added to the staff." It doesn't hurt your chances that you're a post-doc at JPL, but no guarantees whatsoever. You have to really demonstrate that you are qualified to be a staff member at JPL, and you also have to be very lucky that there's going to be an opportunity there for you. I had to do both of those things. I had to prove that I was JPL material, and I had to find the places where I could support myself if I were to become a staff member. What you do in order to make that happen–I think the story is the same now as it was then–you write research proposals to show that you can get your own funding as a principal investigator. In some cases, maybe be part of instrument proposals. But also, find projects on lab, if you're a post-doc, that would support you as a staff member. I found a project, because I had this experience in radar, and I knew the folks who were building radars for JPL, a lot of the same people were involved in the Space Shuttle radar missions. That was a big factor in my getting onto the staff at JPL, that I got involved with the terrestrial shuttle radar mapping missions, of which there were three in the 1990s into 2000.

ZIERLER: What were those three missions?

PLAUT: Prior to those missions, there was Shuttle Imaging Radar, SIR-A and SIR-B. And the principal investigator for SIR-A and SIR-B was Charles Elachi. These were really JPL-centric kinds of efforts, and JPL was the world leader in developing the technology for digital imaging radars. This was part of what I was talking about earlier, the digital revolution. When it came time to do SIR-C, it was to demonstrate a kind of system that could eventually be a free-flying satellite orbiting the Earth, doing imaging radar for science, and also for more practical applications like forest mapping, hydrology, agricultural monitoring, ocean monitoring.

There are a lot of different ways you can use radar data and apply them to problems, not only scientific, but other kinds of terrestrial applications. That was a wonderful project to work on, it was very exciting because the radar was mounted in the cargo bay of the Space Shuttle Endeavor, the same Endeavor that's now at the Science Center in Exposition Park here in LA. It flew twice, and we flew six months apart, so we caught the seasonal changes on the Earth. If I remember right, that was 1994, April and October. Very interesting to see the seasonal changes and other kinds of geologic changes, volcanic lava flows from one to the other. And then, about five or six years later, we used much of the same hardware for the Shuttle Radar Topography Mapping mission, SRTM, which was an incredibly ambitious and incredibly successful mission to map the topography of the land of the Earth in two weeks. It actually accomplished that.

ZIERLER: How is that even possible? Two weeks seems insanely ambitious.

PLAUT: [Laugh] Go look up the Shuttle Radar Topography Mapping mission, and there's a fellow who's now retired from JPL named Michael Kobrick. This was really his brainchild. Really amazing that it happened. Instead of flying over an area twice to get radar stereo–it's not exactly stereo, it's actually called radar interferometry–you have two antennas, one way out on a boom separated from the main antenna. You transmit from one, and then you get the echoes at both antennas, and you can combine these two to make topographic maps. Even to this day, most of what you see in the topography, say, at the US Geological Survey or on Google Earth is SRTM topography, that's where that comes from.

ZIERLER: Did you get a chance to interact at all with Charles Elachi during this time?

PLAUT: Absolutely, yes.

ZIERLER: He's known now, of course, as the former director. What was he like when he was fully involved in the science and the engineering?

PLAUT: He was on the Magellan science team, and he was also one of the leaders of these shuttle radars. I worked on both of those projects, so we crossed paths frequently. I think people will tell you Charles is a very down-to-Earth guy, very easy to talk to, very friendly. He's very interested in whatever it is you're doing. When he was the director, that was such a positive way for a director to be perceived. You run across him in the hallway or the cafeteria, and he'll say, "What are you working on now? Tell me more about it." I always felt very lucky to know him personally. It doesn't hurt to have a personal relationship with the director, and also for him to understand exactly what it is you do because you're kind of from the same world scientifically. That was great. And even in the following years, he participated in some of our Mars radar work, and he would come to meetings. He's on the REASON team on Clipper. He comes to the meetings, and he brings a certain gravitas just because of his experience base and what he accomplished, not only as a director but scientifically in the past, developing radar systems. And I consider him a friend. I love to chat with him. He's great.

ZIERLER: Did you get to experience in real-time his interest in thinking about SIR-A and B and its applicability in Earth science?

PLAUT: A lot of that had already happened by the time I got to JPL. Recently I was assisting with some of the upcoming Venus missions, the two radar missions that are in the works now, VERITAS, the NASA mission, and an ESA mission called Envision. I was doing some collaborations with those folks. Suzanne Smrekar is the principal investigator at JPL for VERITAS, and we were out at our old field sites in the Mojave Desert. I was like, "Oh, I've got to rack my brain to remember what's going on here. That was, like, 25, 30 years ago." But in the process, I dug up some of the literature of the first people to study these areas with radar, and sure enough, there's Charles Elachi studying the lava flows and the sand dunes in the Mojave Desert with radar, with some of the very first radar for geology studies. He was a groundbreaker there. Radar is his thing, but he has a very strong and deep understanding of geology, the geology of California, and the geology that you can learn from radar. That's another real strength, I think, of his legacy, making that connection. And that's sort of how I was trained, to have that link between the geology and the processes, and what you see in the field and what you get out of the remote-sensing data.

ZIERLER: From there, how did you start to transition into Mars science, Mars exploration?

PLAUT: The very first project I worked on as a dedicated planetary geology graduate student was Mars. I had been in the Mars world, and like I said earlier, Ray was like, "Which is it going to be, Mars or Venus?" The first project when I arrived in the summer, before I started classes in graduate school, Ray and his team had me studying the south polar cap of Mars and the region surrounding it. I wound up making a geologic map, even though at the time, I was not a trained geologist. I did my best. And eventually, it turned into a publication, so I had a publication on my list in Mars science, the date of which is 1988. That was my first paper. Fast forward now to 2007, I wrote another paper on the south polar region of Mars using the radar instrument on Mars Express called MARSIS.

In between those two events, I had done a thesis on Venus, and I had done the terrestrial work supporting the shuttle missions. Really, what happened was, there's the radar section at JPL, section 334. If you don't know about JPL sections, that doesn't mean anything to you. For JPL-ers, they know who 334 is. Everyone knows the radar section, 334. And because of my links going back to graduate school with the aircraft program, with Magellan, with the shuttle, all of those were 334 projects. I had tight relationships with them. And the next thing coming up was actually a Europa radar sounder. "What are we going to do with Europa? This is coming up. Looks like NASA wants to do a mission." I was the planetary scientist geologist that they knew, so I got recruited to work on planning for a Europa radar. We did a lot of work, including building a prototype system that we flew in Antarctica to try to see Lake Vostok under the ice cap because that's probably the best Europa analog on Earth.

And then, that whole thing got kind of put on hold. In the meantime, an opportunity popped up to do the same thing on Mars, on what became the Mars Express mission that ESA was doing, which was to re-fly instruments from a failed Russian mission, Mars '96. Our Europa study turned into a Mars sounder study, and we continued a longtime collaboration between Italy and JPL on radar projects. In this case, the Italians were the lead, but JPL built half the hardware for the MARSIS radar. That became our Mars radar science effort and became a big research topic for me. Right around that same time, the JPL Mars program was finally back on its feet after several setbacks. One setback was the post-Viking hiatus. There was just kind of a malaise in NASA's pursuit of Mars stuff after Viking.

ZIERLER: What was your sense of that? Why would there have been that lack of appetite?

PLAUT: Well, there may be a couple factors. One was that when Apollo ended, the idea of the follow-on manned mission being Mars also sort of evaporated. Mars as an ultimate destination got taken down a few notches in NASA and national priorities. I think if Apollo had transitioned to, "Now, we're sending humans to Mars," then the unmanned planetary exploration of Mars would've accelerated, if anything, after Viking. But instead, the manned program turned into the shuttle, and Mars just kind of drifted off of people's radar screens. Also, some people will say that the lack of positive life detection on the Viking landers also harmed the Mars program. Obviously, if we had found life on Mars, that would've changed what we did on Mars. But I think many people were of the opinion, "Okay, we looked for life on Mars. We didn't find it. We're done." Right?

It wasn't until Mars Observer, which I mentioned before, which ultimately failed to get to Mars, and it became Mars Global Surveyor just a few years later. But that wasn't until the mid-90s, so there was a gap from launch of Viking to the launch of the next JPL Mars orbiter of 20 years. A couple of things contributed to that. But then, everyone got excited about Mars again. Part of that was due to the finding in one of these Mars meteorites that was collected in Antarctica that had tantalizing evidence of life. Turned out, these days, most people don't believe it had anything to do with life. But still, some of us remember that President Clinton actually had a press conference to announce this. [Laugh]

That was definitely high-profile, and that got the Mars program really revved up. I think right around the same time, we were doing Pathfinder, so we were relearning how to land on Mars. Then, all of a sudden, we were doing two Mars launches each opportunity, basically going to Mars on the average of one spacecraft a year, whether it was a lander or a rover. We had the setbacks with the Mars '98 Climate Orbiter and Mars Polar Lander, which we recovered from with Mars Odyssey, so I was right in the middle of that. The NASA headquarters folks, and I think Elachi himself, told us on Mars Odyssey, since the last two JPL Mars missions had failed, "You are not allowed to fail." [Laugh] Not to put the pressure on or anything.

ZIERLER: Did the mission failures affect your day-to-day at all? Besides the additional pressure, did it culturally change people perception of risk-taking? What did that mean for you?

PLAUT: It was something called Faster, Better, Cheaper. It was the paradigm of, "We can accept more risk. Let's just not spend quite as much money but send more spacecraft, cross our fingers, hope everything works, and we won't bust the budget. Congress will be happy." There are some things to be said for that paradigm, but really, you have to be able to accept the failures, and have redundancy in your program so that if one thing breaks, you have another version that you could send to replace it. When we had the twin failures in '98, that whole paradigm kind of dissolved, and it was recognized that the black eyes were just a little too much for us to absorb to say, "This is the right way to go about things."

Then, what resulted was a much more risk-averse approach to doing these missions, which meant going by the JPL design principles, and the main one is, test as you fly. That is, everything you're going to do in-flight, you have to demonstrate works before you launch, and you have to show why it's not going to break, that your risk of failure is tiny, and these things are going to succeed. Something like the entry descent and landing to Mars, where you have hundreds of different events, and mechanisms, and steps, any one of which will destroy you. You have to do an incredible amount of testing. It's just expensive. Like I was saying about Mars Sample Return, there are no technical barriers, it's just technically complicated, difficult, and expensive to make sure that you're going to succeed. That changed the operating principles for the Mars program.

And it changed something very specifically for where I was at the time, which was just starting on the 2001 project, which became Mars Odyssey 2001. We were an immediate follow-on and a mirror image of Mars '98. It was the same opportunity, same Mars launch window opportunity, a lander and an orbiter, and they're supposed to work together. That's what Mars '98 was, Mars Polar Lander and Mars Climate Orbiter, and that's what 2001 was supposed to be. Because of the failure of Mars Polar Lander, they said, "We're not ready in '01 to do another lander with the same design." And it was the exact same, a clone, basically. We struggled, on the 2001 project, to try to demonstrate, "No, we know how to do this. We can do this without the risk of failure, the problems that Mars Polar Lander had." But they eventually pushed that aside. 2001 became the orbiter only, and it became Mars Odyssey. Like I said, they told us we couldn't fail, and I guess we made sure we didn't.

ZIERLER: Between both missions, given how long-lived they are, what's surprising about that, and what makes sense, looking back?

PLAUT: The things that are still going now on the NASA side, which are really quite amazing–just about everything goes much longer than you plan for.

ZIERLER: Just so I understand, radar sounder is not extant, it ended?

PLAUT: In 2001, we launched Mars Odyssey. Still going. Does not have a radar on it. That's the project that I'm project scientist on. It has a camera, neutron detectors, a gamma ray spectrometer. In 2003, ESA launched Mars Express. That has a radar sounder, still going. That's 20 years on. Odyssey's been 22 years, Mars Express has been 20 years. Mars Reconnaissance Orbiter, which also has a radar on it, was a JPL mission launched in 2005, so that's pretty remarkable that that one's still going, too. To get back to your question. The amazing thing about these orbiters is just how robust the hardware is. I'm totally blown away. [Laugh] For the radars in particular, Mars Express radar, I saw this when they were hooking it up together in the facility in Rome. We were in the clean room in our bunny suits, and we saw the boxes. I thought, "Okay, well, let's hope this works." Never in my wildest dreams did I imagine it was going to work in Mars orbit for 20 years. That's just incredible to me.

ZIERLER: Does that include the power supply, the fact that it continues to go?

PLAUT: Yeah. It's solar powered, and these solar panels degrade but don't wear out. Really, at this point, for Mars Odyssey, the biggest concern is probably the propellant. We don't use propellant to stay in orbit. We get into an orbit that, because of physics, will not decay, so we just stay there. We need to use propellant on all of these orbiters to keep our pointing, to point the spacecraft so the instruments can see their targets. It's what's called the attitude control system. The orientation of the spacecraft, the attitude, is controlled by these heavy spheres that are called reaction wheels. They're basically gyroscopic spinning reaction wheels, and they operate on three different axes. And by speeding up or slowing down one of the three, it causes the equal and opposite reaction of the spacecraft to rotate. The problem is that when you stay in a particular orientation, in the case of most of the Mars orbiters, pointing down to the surface of Mars, gravity is trying to turn the spacecraft constantly, and you're trying to keep it in a certain position.

And that generates momentum on these wheels, which eventually has to be spun down. In order to do that, you have to fire thrusters using propellant. That's where the propellant goes, to maintain the attitude of the spacecraft. On Mars Odyssey and Mars Express, we're getting to the bottom of the tanks of the propellant. We've done all kinds of fuel-saving techniques and tricks, we don't fire the rockets to change the orbit or anything like that, we just want to keep it alive as long as possible. With the computers on these spacecraft, you can't do anything except maybe update the code a little bit. They are from a different century, literally. This is 20th-century technology in those computers. Windows 2 or 3 or whatever.

ZIERLER: We almost didn't even have cell phones when those things launched.

PLAUT: Yeah, there's 1,000 times more compute power in your pocket than is onboard any of these spacecraft. They were designed to operate with what they had, and they're still going. It's a bit mind-boggling to think how far the computer power, data storage, and all those things have come since then. One advantage that particular generation of spacecraft had over their predecessors was solid-state data memory storage as opposed to tapes. Most of the previous era missions stored their data on tapes. Literally, there were tape recorders, and the tape was spinning back and forth. Those things would not last 20, 25 years. But solid-state memory, as long as you don't have any kind of electronic degradation or solar radiation storms bombarding your circuit boards, you can keep those things alive. I think that helps us a lot.

ZIERLER: Given the happy surprise of the length of the mission, have the science objectives changed over the years? Have you been able to do new things that weren't conceivable? Or is it more like you've been able to do the science at a deeper level because of the timeframe?

PLAUT: For the NASA and ESA missions, every few years, you have to justify your existence. You have to make a request to extend your mission. Right now, the NASA missions are on a three-year cycle. There's something called a senior review board, a blue-ribbon panel of mostly outside experts that you submit a proposal to, and they decide whether you're going to do science that makes it worth NASA's money to continue the mission. Let's talk about Mars Odyssey. There are two parallel approaches we use when we're asked to justify our existence and talk about what we're going to do for the next three years. One is to extend the record of what we've done so far in the same way. A lot of times, that's not a very appetizing thing to ask for. "Oh, you're just going to do more of the same. What's the value in that?"

But fortunately, for Mars and for the kind of measurements we're making, we're talking about climate history. We're getting a record of multiple Mars years, which is about two Earth years each. In our case, we're on our 10th or 11th Mars year with Mars Odyssey. Each Mars year is remarkably similar to the past, but what is really interesting to the climate scientists is the small differences from year to year. We're able to establish a baseline for what is the normal Mars year, but then, "What are these anomalies we see?" Particularly, the dust storms. There are dust storm years, and then there are reverberations and impacts that follow on from the dust storm years. We make the case, and I think we've made it successfully on Mars Odyssey, that extending the climate record, this kind of unique but continuous climate record, is valuable.

The other thing we are always asked to and required to do is determine, "What are you going to do that's different and exciting?" That's always a challenge. But we have been able to come up with a lot of great things to do with the Odyssey instruments and spacecraft that we never really thought we would do on the original mission. A lot of it involves pointing the spacecraft in different directions. We had a comet flyby. There was a comet called Siding Spring that flew by Mars. We were able to capture data when that came through. We've observed Phobos and Deimos, the moons of Mars. That was not part of our original objectives. Normally, for Mars Odyssey, we just point directly beneath the spacecraft at all times. But we've found there's a lot of value in moving the spacecraft back and forth and capturing images from different angles. The special camera on Mars Odyssey is THEMIS, a thermal infrared imaging system.

As you look off to the side, the way the surface materials emit their thermal infrared radiation changes dramatically, and it can tell you more about what's going on at the surface than you could get from a single observation. Another thing we've done on Mars Odyssey, and again, this is related to the thermal imaging, is change the time of day of the orbit. Initially, we were flying in what we call a pre-dawn and late-afternoon orbit. On the night side, we were flying over the terrain at its minimum of temperature just before the sun came up, and in the afternoon, we were in the warm part of the day. Say, like, 4 am, 4 pm, that time of day. We shifted the orbit so on the day side, we're at the morning side, like, 7 or 8 am, and then on the evening side, we're at post-sunset. The way a surface warms up and cools down in response to the diurnal cycle, the sun rising and setting, is very different depending on what time of day you're looking. That was a big change we made that gave us a whole new way to use the spacecraft and the instruments.

ZIERLER: Given the success of the rover missions, given the way that the public gets excited about them, did that change any of your Mars science at all?

PLAUT: It doesn't directly change the way we operate the orbiter missions. Of course, we do interact with the rovers, as I explained. We collect data, we relay the data from their science instruments through the orbiters. We certainly use the orbiters to select and characterize the landing sites. That's always an element of the orbital science. With the plans for someday sending humans to Mars, there have been workshops, some of which I've been involved in, for identifying landing sites for some of the first human missions. "Where would be an interesting place to go? Where would be a safe place to go? Where would be a place there are resources the astronauts possibly could use, such as ground ice, that would be easily accessible and retrievable? Are there geologic materials that might be of use for constructing habitats, or paving roads, or things like that?" There is still an element of surface science that the orbiters are always kind of keeping an eye on.

ZIERLER: When you start to get involved in the mid-2010s, both in Jupiter Icy Moons and Europa Clipper, is the timing there to suggest that Mars Odyssey was stable at that point, and you simply had the bandwidth to go on and look for other projects?

PLAUT: If there's something interesting, I will pursue it. At JPL, we talk about filling out our time card, and many people have the problem, "I don't have enough work to do to fill out my time card. I've got to go find something else." But other people have the opposite problem, which is, "I have too many things to do, and I'm leaving somebody short-changed because I'm not doing what I'm signed up to do on their project. There aren't enough hours in the week to do it." But I've managed to make that work for myself. If there's an interesting project, and sending these radars to the icy moons has always been something that I wanted to pursue, regardless of what else was going on on my time card, I was going to sign up for those, for sure.

ZIERLER: What was compelling in thinking about the icy worlds in Clipper? It's JPL, there are so many fun and cool things to get involved in.

PLAUT: Because of the liquid water element and the connection to life, it just seems like it's right up there with the highest priorities of planetary science. Also, I have some kind of personal history with that. I'll go back to our discussion of my undergrad days, when I was in the class of Jim Head. This was a class called Planetary Geology, and it was meant for upper-level undergraduate geology majors and graduate students. I was neither, I was a music major, but I signed up for it anyway. At the end of that semester, everyone had to write a term paper. I thought a nice topic for a term paper–remember, this is 1980–was biological possibilities of the Galilean satellites of Jupiter. And this was when Voyager had just done its fly-bys of Jupiter. Also, there was a recent development in the world of geology, where at the seafloor spreading centers, the significance of which had only just recently become obvious for plate tectonics, it turned out there were communities of organisms living there that had no obvious link to photosynthesis.

They were living on chemical energy from the hydrothermal, geothermal vents at these volcanoes, at the spreading centers. I thought, "That might be kind of a neat way to put two and two together." Because what Voyager was finding at the icy moons was, they have rocky centers, and then they have oceans, and then they have ice on top. But at the bottom of those oceans, you should have liquid in contact with rock, and maybe there are volcanoes there, and maybe that becomes a habitable environment. That was the thesis of this term paper. I banged it out on my manual typewriter over maybe four or five hours and put that in there. I've been thinking about this for a long time, about what was going on there. And by the way, Jim Head gave me an A-plus. I have to say, that positive response at that time was something that said to me, "Okay, maybe I have a knack for this." Looking back on it, I still have the paper, and I thought, "I could've submitted that to a journal." [Laugh] But it was the end of the semester, he probably wanted to go off to Cape Cod or something, so he didn't try to get me to write that up.

ZIERLER: For the icy worlds and Clipper, for all of your experience and expertise you had built up for Mars, what was transportable? What was really relevant, and what was brand new for you?

PLAUT: Certainly I was familiar with the technique, the radar-sounding, ground-penetrating radar. When we were proposing the instruments, both RIME and REASON, we needed to explain how we would get from our instrument measurement to a discovery, a conclusion, a finding about the interior of these icy moons. There are a lot of steps there from collecting the data to writing the paper with your discovery. I felt like the experience we've had with Mars was extremely valuable in making the connections from points A, B, C, D, etc. that could get you there. In particular, what data product do you need, and how do you interpret that data product? How do you extract information from that data product that allows you to make a geological, structural, geophysical, chemical interpretation? Whatever it is you're trying to learn about the target. It's a combination of a technical way of going from the measurement to the answer, but also a philosophical or logical way. "What steps do you have to go through?" I think we made the case that we understood how to do that in our proposals. It was much more difficult to do that when we first proposed to send a radar to Mars because nobody had done it before. But since we had the Mars experience, we could use that in our proposals for the Jovian moons to demonstrate, "Yeah, we know how to do this. This is doable."

ZIERLER: Within both missions, what was mutually beneficial? What could you apply from Clipper to the icy moons, and what could you apply from the icy moons to Clipper?

PLAUT: Let me say a little bit about RIME and REASON. RIME flies on JUICE, and JUICE is primarily targeting Ganymede, the largest moon of Jupiter. Clipper, which carries REASON, is focused almost exclusively on Europa. Both of them will fly by several of the moons, so both of them will see all three of Europa, Ganymede, and Callisto. Io, which is the volcanic moon, is not icy. It's too close to Jupiter, too far into the radiation zone, that neither spacecraft is going to visit Io. But they are both going to visit the three icy moons. But the focus of each, JUICE and Clipper, are very different in terms of which is their main target. JUICE is mainly looking at Ganymede, and it will eventually get into orbit around Ganymede. Clipper will just fly by Europa many dozens of times. It'll be orbiting Jupiter the whole time, it's not going to orbit Europa. But it'll fly by Europa enough times that it will build up some nice maps of some of the regions.

Then, the radars have a part that's identical. RIME operates at one frequency, the center frequency is nine megahertz, and that's about a 30-meter wavelength. REASON has almost a duplicate of that system. That's going to be very powerful because we can make basically directly analogous measurements of different targets with the two instruments. We can look at Ganymede with RIME, we can look at Europa with REASON, and it's going to be apples to apples in terms of the measurements. We also will have visited both bodies with the other, so we can cross-calibrate as well. We're going to fly by Europa a few times with JUICE, and we'll cross over some of the areas that Clipper will also see, so we'll have data over the same target. Likewise, Clipper's going to visit Ganymede a few times, so we'll be able to compare that.

And then, Clipper also has a higher-frequency radar, which is meant to explore the more shallow subsurface at higher resolution, and that's on REASON, but RIME does not have that. That's going to be an interesting thing as far as the value of using that higher frequency, the VH, on REASON when we fly over Ganymede with Clipper. That will supplement our JUICE study. REASON on Clipper, by having the two frequencies, is a much more capable kind of radar. The two will work together, and we have many team members who are on both teams and some who are on just one or the other. We're coordinating a lot of our work together. I think the two will be operating at the same time for much of their missions. It'll be really interesting to see how they interact. Certainly, between the two radar teams, we've got a lot of synergy and collaboration going.

ZIERLER: Moving our conversation closer to the present, when COVID hit, what did that mean for your research? What did it mean for all of the complications of keeping the missions going?

PLAUT: I think the biggest challenge that I observed was that we were in the home stretch of building, testing, and delivering the RIME radar to ESA when COVID hit. The launch was in '23, in April. But actually, at the beginning of COVID, we were planning to launch in '22, so it was two years from launch. And that's pretty close to launch. ESA likes to get their deliveries well ahead of the launch date. They usually front-load their schedule compared to the way NASA does. We were scrambling to make our delivery times before COVID hit, and then once it did, that was a huge challenge. And most of the work was being done in Italy, and Italy was especially hard-hit by COVID in the beginning stages. Our scientific collaborators are in the north of Italy, which was the worst part. That was quite scary, quite difficult. We had hardware that we were working on at JPL that had to be hand-carried on aircraft to get to Italy.

Turned out, some of it failed. We had to bring it back, then send it out again. All kinds of logistical nightmares and COVID layered on top of what we were trying to do. It would've been tough enough as it was. I really want to give some kudos to our project manager at JPL, Don Heyer. He did an incredible job to shepherd this project through that. For me, personally, I had some very successful work and accomplishments during COVID, working from home. It didn't really slow me down. In particular, working with interns, I did two fully remote internships, one with an undergrad, one with a grad student, and they were both extremely successful. I'm sure it would've been better if we could've been together in person, meeting daily, but somehow, I think part of it may be that the students got the knack for working remotely because that was their life during COVID. They were doing all their classes remotely. In a way, working one-on-one, I think, was maybe a relief for students compared to being in a Zoom class. To me, that seems like a nightmare. But working one-on-one in a Zoom meeting like this conversation we're having now, I got used to that very quickly. It was a very productive time for me, as it turned out.

ZIERLER: Moving our conversation right to today and looking to the future, what are Clipper and the inevitable power shortages for Mars Odyssey going to mean for your overall responsibilities six months, a year, two years into the future?

PLAUT: I'm not too worried about that at the moment. Part of it is, there is retirement on the horizon somewhere out there. One scenario that's often available to JPL-ers is a sort of a partial retirement, where you come back and work part-time for the things that either the Lab thinks you're of value to the Lab for, or things that might interest you that you want to keep your hand in. I would say for sure, the icy moon missions, both JUICE and Clipper, I would be interested in staying on. I can see this evolving quite naturally and not being too difficult of a period coming up in the next five years or so.

ZIERLER: Now that we've worked right up to the present, I want to ask a retrospective question, and then we'll end looking to the future. Looking over the course of your career, then thinking about the next generations, where the future missions are going to go, what aspects of your work and contributions do you look at in terms of enabling those next generations of researchers, technology, science? What have you created that might be a foundation or stepping stone to those projects in the future?

PLAUT: Interesting question. Part of it, I think, goes back to when you asked what I consider some of the more significant discoveries and findings that I've been involved with. I think the ice on Mars piece will continue to have reverberations. I was involved over the past couple years in a study that NASA commissioned to look at how we can study Mars with our newest technologies to understand ice as a resource for humans. That's really the next step. That's where that's going next, and it turns out radar is probably going to be a big part of that. We had a study team which identified a certain kind of radar that would be able to map out the locations of ground ice and determine how suitable it might be for utilization by a human crew. I think that's definitely a big part of it, then in parallel with that is, of course, the life question. Because it's H2O, albeit in solid form, it does really have huge implications for life.

ZIERLER: Finally, looking to the future, you've already sort of shared your intentions. If the interest or possibility is there to stay on even after you retire, it begs the question, what's so compelling for you? Why would you want to stay involved beyond when you would have to? What's most important? Where do you want to be as these discoveries get made?

PLAUT: I think a lot of people at JPL and probably at Caltech as well, in a cocktail party conversation, will say, "I have one of the coolest jobs in the world." Or maybe the person you're talking to will say to you, "Wow, you have one of the coolest jobs in the world." [Laugh] I still say that because one of the things that always stuck with me that Carl Sagan would say is, humanity, is an example of the universe becoming aware of itself. That's what consciousness and now also technology is. We're part of the universe, and we're reflecting on that universe by telling a story about it. To me, that's what planetary science is as well. It's taking our human experience as one example of consciousness that's evolved in the universe, and then applying it to different questions, mysteries about the universe itself. For example, on Magellan, looking at a kind of volcano we had never seen before on another planet for the first time, or peering into the ice caps of Mars the way nobody had ever done before, and now coming up in the future, looking underneath the ice of Ganymede, Europa, and Callisto for the first time, you can't beat it. That's really what it's all about, and I just feel so fortunate to be part of that endeavor.

ZIERLER: On that note, I want to thank you for spending this time with you. It's been a terrific, wide-ranging, and really interesting discussion. I do appreciate it.

PLAUT: Thanks, it's really been fun for me as well.