Matt Golombek

Matthew Golombek

Senior Research Scientist, Jet Propulsion Laboratory, California Institute of Technology

By David Zierler, Director of the Caltech Heritage Project

November 10, 2023

DAVID ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It's Friday, November 10th, 2023. It's my great pleasure to be here with Dr. Matthew Golombek. Matt, great to be with you. Thank you so much for joining me.

MATTHEW GOLOMBEK: My pleasure.

ZIERLER: Matt, to start, would you please tell me your title and institutional affiliation?

GOLOMBEK: I'm Research Scientist, Senior Research Scientist at the Jet Propulsion Laboratory.

ZIERLER: Tell me some of the things that you're working on right now. What's interesting to you?

GOLOMBEK: [laugh] Lots of things are interesting, probably more than I can work on. [laugh] I'd say the biggest chunk of my career has been selecting landing sites on Mars. It's the kind of topic that really you can only do at JPL. It's finding a place where the spacecraft can land safely and do interesting science.

ZIERLER: What's happening in Mars science right now? I know there's always a sequential narrative of one mission that's going on, one mission that's getting close to being launched, and something to be planned far out into the future. What are you involved with in those three chronological aspects?

GOLOMBEK: The past 20 years has been the renaissance of Mars science. There have been just about a mission every possible launch opportunity, which is once every 26 months when you can go to Mars. We've probably had a dozen missions in that timeframe. It's been an incredibly interesting mix of both orbiters and landers, and the data has fed off each other, both an orbital view and a surface ground truth, if you will, view. [laugh] It started with Pathfinder in the late '90s, went to Mars Global Surveyor, Mars Odyssey. There's been the Mars Express from the Europeans, Phoenix Lander, the Mars Exploration Rovers. There has been whole series of rovers and orbiters that have really uncovered a huge suite of fascinating information about Mars. Right now, we're in the first part of a very ambitious effort to try to return samples from Mars. The first of that is the Perseverance rover, which is selecting cores that are placed into little test tubes, if you will [laugh], and sealed. They would be picked up by a subsequent lander, and brought back to Earth. Most of the advanced mission planning right now is for what we call Mars Sample Return, which is towards a whole number of missions that would be required to get those samples back into laboratories here on Earth.

ZIERLER: Matt, what is the state of play with Mars Sample Return? How advanced is it?

GOLOMBEK: It's called a program, but in project management terminology, it's in what we call Phase B, which is where a project completes technology development, engineering prototyping, and assessments of heritage hardware and software. It is extremely ambitious. The reason it's called a program instead of a project is that it takes two or three different missions to complete the task, all of which are large, complex missions. In addition to the rover that's there now that is picking up the samples, there needs to be a lander that goes and lands near that rover, and transfers the samples from the rover. If the rover cannot deliver the samples, in the current baseline plan, Sample Retrieval Helicopters based on the highly successful Ingenuity helicopter brought to Mars by Perseverance could collect 10 tubes that were left on ground at the Three Forks Sample Depot in Jezero crater in January 2023 as a backup. Those samples are placed into a return container. It's sort of a ball, if you will. [laugh] That containment vessel is put on top of a rocket, and launched into orbit around Mars. Then you need another spacecraft that goes and finds that ball, and captures it, and brings it back to Earth. Then you have to land it safely and securely on the Earth. That's two or three missions, as well as once the samples do get to Earth, they need to be evaluated for safety in a high-containment facility that's similar to current biosafety laboratories, in order to keep those samples sequestered from any biota on Earth until proven safe for release or sterilized. Each chunk of these steps is a complex and difficult engineering task that can also be quite expensive. [laugh]

ZIERLER: When you put it all together?

GOLOMBEK: Yeah, [laugh] probably the most expensive aggregate in terms of Mars missions that we've ever tried to do.

ZIERLER: Matt, thinking about the expense, obviously this requires ongoing support in Congress, from Washington, D.C., from NASA. What is the case to be made that this is such a compelling mission that it's worth doing this?

GOLOMBEK: I think that goes to why Mars is a compelling target. As far as we know, right now, the only planet that has life on it is Earth. It's very clear that the sole requirement for life is liquid water. Of all the other solar system bodies, the only one that we have clear and unambiguous evidence that liquid water existed at the surface is Mars. It occurred at a time when life first got started here on Earth. The oldest microbial life on earth is about 3.6 billion years old. At that time, Mars was a very different environment than it is now. There were clearly lakes. Perhaps there was an ocean. There was liquid water that drained across the surface, and created gullies and channels. There were even deltas where those channels entered into standing bodies of water, and deposited the sediment. Those deltas are incredibly biogenetically rich environments on Earth. There are lots of nutrients that are brought in, and there's a ton of biology that occurs in those water systems. That's in fact where Perseverance is - exploring a delta, and an ancient one, on Mars. The question is, what does it take to form life? Will it form anywhere that liquid water is stable, or is there some other [laugh] chance occurrence that went into this? There's no place that you can study a question with, I would say, almost theological importance as that. It's right next door in the solar system. It's a little expensive to get to, but it's not impossible. [laugh] You can address a question of that importance in a scientific manner. I think that's what drives and has driven the Mars Exploration Program, and clearly is what's driving the intent to get samples back.

ZIERLER: Now, the whole idea here is that there are facilities, laboratories on Earth that can make measurements and do studies that simply would not be possible in situ. In other words, any lab that we might send to Mars simply couldn't give us a richness of understanding and data that we can get back here. I wonder if you can explain just how much better it is to have these samples here, to look at the questions that you've explained.

GOLOMBEK: Some of the instruments that we use to look at the detailed geochemistry and interiors of these rock samples are as big as your laboratory room. Some of these instruments, you build a laboratory to accept them. They're that large. Anything that you send to Mars is under intense scrutiny for mass and power, and everything has to be miniaturized. You're going to spend a ton of money on these instruments to try to get them to do just a small portion of what you could do with the laboratories here on Earth. Plus, if you have those samples, maybe we design some instrument in 10 years that can do something that we don't even know about now. You have that sample, you can then begin that investigation. Having a sample here on Earth is always better than trying to miniaturize some instrument, and stick it on top of a spacecraft, which is the most complex, probably expensive things that humanity can build. [laugh] Everything is miniaturized, and has to fit together onto this robot that is being sent into extremely difficult conditions, and has to land on another planet before it can even start to do its work [laugh], no less rove across the surface and find the samples. If you have the samples in the laboratory, you can always investigate far beyond anything you could even dream of doing on a spacecraft on another planet.

ZIERLER: Matt, so I understand the sequencing and the decades-long planning that's going into this endeavor, is that to say that Mars Sample Return was conceived within the boundaries of Perseverance? In other words, the capabilities of Perseverance, and its capacity to drill and take core samples, only make sense if there's a follow-on mission to go and get those samples.

GOLOMBEK: Yeah, that's right. There was a conscious decision by NASA to make collecting samples a part of Perseverance's science objectives. For those of us that are on the inside, that has dominated a lot of the operations of that spacecraft. It is hard work to find a diverse suite of samples that can be related to each other in a stratigraphic framework, older and younger. You can see how this system evolved and changed over time. Yes, that was a first step. At the time that decision was made, there had been no decision about whether there would be a sample return, but it was believed that that was the first step you needed to do to begin to think about the next steps. I would say that Perseverance has been so successful, and the rock samples that it's already obtained is a compelling suite of samples that you would love to return if you had the choice. That's just not me saying it. But all the national academies and all of the large august groups that weigh in on these things have all basically said that same thing.

ZIERLER: Let's go into a little more detail about what Perseverance is getting, and what its capabilities are. Mars, it's a big planet. How far can it traverse across the surface? How do you know how to define a diversity of samples, and what is it capable of collecting in terms of depth, in terms of mass, in terms of density?

GOLOMBEK: Some of that starts with the selection of the landing site, which I'll describe at some future time when we get back around to it. [laugh] But what you want is a suite of samples that can address the major scientific questions that the mission is designed to do. This mission is designed not only to take those samples but to go beyond what the previous missions do. The previous mission showed that Mars was a habitable environment at 3.6 or so billion years ago. The Mars Exploration Rovers, as well as the Curiosity rover, have shown that there were liquid water systems at that time that were neutral pH and conducive to the formation of life. Not only that, the Curiosity rover, the previous one before Perseverance, showed that in that water system in Gale crater, everything you need to support life existed. Carbon, hydrogen, oxygen, nitrogen, phosphorus, it was all there.

There were very interesting things happening within the lake that could have been an environment in which life could have gotten started. The next question is, did life form there? The best way to answer that is by returning samples. That's an extraordinarily difficult thing to do in situ. Even the way we do it here on Earth is you culture the sample, or in the case of paleontology, you have the remains of that. Those are all very difficult tasks. You want a water-rich system that existed at the time when liquid water was stable. If you had those rocks deposited in water, and in a water-rich system like a delta, which, as I already said, are incredibly biota-rich environments, that's a wonderful place to go. That is, in fact, why Perseverance went to Jezero crater, where there is a deposit that was clearly a delta when it formed. Jezero lake was full of water, and there's a river that is now dry but that entered, breached the wall of the canyon of the crater, and brought sediment in, and built out a series of very diagnostic rock facies where the size fraction of the material that's brought into the water is sorted by the distance from where the river enters the lake. The finest grain material that's clay-rich, micron in size, and very conducive to any biological activity but also to sequestering it, that is, if it existed, to capture it in the rock between these clay particles that are deposited in the bottom of this lake. Those are the kind of samples that Perseverance is getting. They've gotten clay-rich sediments at a variety of locations. They have traversed up the entire delta. They've gotten the whole package of material that came into this crater. Not just that, but this crater is in a portion of Mars that has evidence for ancient carbonate-rich rocks. Carbonate-rich rocks on Earth are deposited by living organisms.

There's a feedback loop on the Earth between pulling carbon, in fact, out of the atmosphere. The way we do that is by living fossils, calcium carbonate or shells or things like that. This is going to go a little bit off topic. But the way the Earth has maintained its constant climate throughout geologic time is a geologic process that allows us to recycle those volatiles via plate tectonics and, in fact, living organisms. Let's put that aside. That's too far to go for now. [laugh] There are carbonate deposits on the rim of the Jezero crater. Immediately adjacent, there are phyllosilicates, that is, clay-bearing minerals that date back to the Noachian period as well. There is a wide variety and diversity of rock types that are central to this main question of, was Mars a habitable environment in the Noachian? What you want is a wide diversity of rock types. You want sedimentary rock types like the delta that I described, as well as some of these others. That's the kind of treasure trove that you want to bring back to Earth.

ZIERLER: The size of the samples, what are we talking about here? Like the size of one's pinky, a bottle of soda?

GOLOMBEK: About the size of a piece of chalk, if you will. It's sort of that thick, and it's placed inside a sleeve, and it has a top which seals it from any outside environment. When it's brought back, everything that was in that tube is still in that tube. The desire is to keep it at moderate temperatures. You don't want to boil it or heat it or any of those things on its full round trip. I think we have room for up to 30 samples, something like that, that fit into this thing that gets launched into orbit around Mars.

ZIERLER: Now, because the samples are relatively small, a bit of a pencil, as you say, that must mean that Perseverance is not drilling terribly deep to gain them.

GOLOMBEK: Right. There was never an intent with Perseverance to drill to depth. What Perseverance can do is it can clean off the outer rind of the target rock, and then it can drill down into the rock to get a clean portion of that rock. It has gotten regular samples from a number of locations, as well as atmospheric samples, and, of course, the omnipresent dust, which is everywhere on Mars, the red dust. That's the assortment of the samples that we want to bring back. Total mass, a half a kilogram. What's that? A pound or something? The other question is, do we have instruments on Earth that can look at really small little pieces of rocks? The answer to that is yes. In fact, there's a tremendously interesting story about what happened to the laboratories after Apollo brought rocks back from the Moon that spurred on development of instruments in a way that very few other things in geology have. I don't think there's any question about the analyses can be done on very small samples. You obviously wouldn't want to use all of one sample in one analysis. You'd want to slice it and dice it, and you'd want to hand it out judiciously—the way they do with the Apollo samples is you write a proposal to get a sample to do some science with it. Only if that proposal is accepted do you then get a chance to do something with that sample.

ZIERLER: Now, because the samples are coming from relatively shallow depths, what is the best response to the concern between radiation and surface erosion? There may have been interesting things to look at billions of years ago, but they're now gone. What's the response to that?

GOLOMBEK: That has been brought up for quite some time. The concern is, in fact, that radiation would damage any organics that might have existed. But that question has pretty conclusively been answered by Curiosity, which has clearly found organics in near-surface rocks, organic molecules, just not necessarily biogenic ones that came from life. The reason that's the case is that there has been erosion of the surface that has taken off the surface layers at a high enough rate that the radiation has not killed and disassembled all of the organics in it. That same kind of environment is clearly occurring in Jezero. You can see that there's been quite a bit of erosion. What we see now of the delta is just a smaller piece of what it was. Those rocks are friable and easily eroded and, no question, that's been occurring. I don't think anybody's too concerned about that issue.

ZIERLER: The samples get home. You mentioned there are some biosecurity measures that need to be taken. What's the idea there, and how far does that get us into science fiction scenarios about what might occur?

GOLOMBEK: You would be bringing samples from an entirely different planet with a potentially different biosphere. Now, any biology could be distantly related to us. We know that rocks from Mars have come to Earth repeatedly through time. It's even been suggested that we're all Martians, not just me [laugh]—

ZIERLER: [laugh]

GOLOMBEK: —that life started on Mars and came to Earth. But still, it is a potential that there could be, I mean, the chance of actual living organism in these samples is really small. But to put safety first, these samples will be put into a containment facility that probably exceeds any containment facility that's yet been built on Earth. Those samples will be tested thoroughly for quite some time before they are let out of that containment environment to be put into normal laboratories. If there's any type of replicating biology in them, then the samples won't be allowed for release out of high containment unless they are sterilized, and there will be a well-tested sterilization protocol. We don't really expect that to be the case.

ZIERLER: Is there also a two-way street concern here that we could influence or damage any potential biological materials in the samples?

GOLOMBEK: Yes, which is why you want to keep the samples separate from Earth's environment—if you bring them back, and they're exposed to biology, just like the Martian meteorites that land without our assistance, if you will [laugh], they're going to get changed by that. Yes, you want to keep them separate. There's three parts to this. Whatever you send there better be clean, because you don't want to bring biology with you, sample it, capsule it, and bring it home, and, say yeah, "we found life. It was what we brought there in the first place." [laugh]

ZIERLER: [laugh]

GOLOMBEK: That's not too bright. That's all part of what we call planetary protection, where anything that goes to Mars is cleaned, and the level at which you clean it depends upon how likely that environment is to have life, now or at some time in the past, and what you're going to do in that environment. All the hardware, must be extremely clean, and you try to keep any microbial material you're carrying down to a minimum. Then, of course, when you bring the material back, you don't want to be adding anything like that to it before you do a lot of the analysis that you need to. In the event something does come back, we also will have the ability to identify it based on a library of samples taken during the hardware development so we can rapidly compare what we find.

ZIERLER: Matt, do you have a sense of where this initial containment facility will be built? Will it be on JPL campus?

GOLOMBEK: It will not be at JPL, that sort of work is not in our heritage. But the location has not been decided. NASA collected a variety of information about the capabilities that such a high-containment facility should have, and they have received some expressions of interests from locations with experience with similar facilities, but that process is really just getting underway. That's all, geez, probably of the order of 10 years away before the samples get back to Earth.

ZIERLER: Assuming that these have been cleared to be safely researched, at that point, will they go to regular academic geology labs around the country—

GOLOMBEK: Yeah.

ZIERLER: —around the world? What would that look like?

GOLOMBEK: I think it'd probably look a lot like the long-term curation done with the Apollo program where samples are held at NASA's Johnson Space Center. First of all, wherever this high-containment facility turns out to be, it would probably have a lot of fundamental laboratory equipment that allows a first-order assessment. One was just a geologist looking at the rock, and saying what they see; thin sections where you look at the petrology, what minerals are in the rock, and those are all kind of standard things. That would probably be done right there and then. But assuming that they're clear, there's no biology or anything like that, the sample would likely be transferred to a dedicated curation facility, similar to Apollo. Then professors or scientists would write proposals to gain access to specific samples, with a proposal that says what kind of science that they're going to do with that sample, what kind of analyses, and what the results might be. Then those would be peer-reviewed, and if they're accepted, then they would get a portion of that sample to do some science on. That's still the way it goes on now with the Apollo samples that were brought back from the Moon. They're kept at Johnson Space Center in the containment facility. If someone wants to look at them, they're packaged up and brought to that laboratory. They do some work, and then they're returned, if it's a non-invasive procedure.

ZIERLER: Because all of the emphasis here is on the search for extant or more likely past life, assuming all of this happens, the samples are studied, however long that it takes, there's some conclusive statement, goose egg, we haven't found any evidence of life, what is the counter media narrative that might say, "Oh, it was all for nothing, all of that cost, all of that effort"? How do you counter that?

GOLOMBEK: Whenever you do more science, you ask more questions. Usually those questions are more directed at the pieces that go into answering that broad piece. It may be that you need multiple sample returns from a variety of different places on Mars to conclusively answer that big, big question, "Was there ever life on Mars?" To think that you would find a particular single sample that would do that, you might have to be pretty darn lucky. [laugh] But, the locations the samples were taken from were based on our best estimates of where to find extinct life. I don't think it's this "black and white;" a "yes or no." It's "were all the building blocks there?" Were there reactions? A lot of single-cell organisms, they don't live on photosynthesis. They're chemists. They live on reactions between rocks and water that occur underground. In fact, the biggest biota on Earth is hidden from view. It's all buried in the pore space underneath the ground, and most of that is not photosynthetic. These microbes are chemists. They're living at the reaction space between water and weathering rocks that create microenvironments where they can use that reaction to fuel biological activity. That's the kind of thing that we're probably looking at. It's not like you're going to land and find a dinosaur bone. A dinosaur is an incredibly evolved species that took three billion years of Earth evolution to create. [laugh] It may be that primitive life is common, but so-called advanced life—if we're advanced—is a much more unusual thing. There's nuances here in terms of framing the question that will further our analysis and answering the biggest questions.

ZIERLER: Matt, in the way that planning for Mars Sample Return was baked into the capabilities of the Perseverance rover, will there be future missions that are baked into Mars Sample Return so that there is a mission after Mars Sample Return that Mars Sample Return itself makes possible?

GOLOMBEK: NASA and its advisory committees are looking at the horizon beyond Mars Sample Return right now. But beyond possible U.S. cooperation in the planned Rosalind Franklin rover, there's no other specific Mars missions after Perseverance that are even really in the planning stage besides the Sample Return campaign. Sample return, as I already said, requires a lot of these different pieces that's going to need a large investment. But I would say, in general, that missions that come along are generally responsive to previous missions. The Mars Exploration Rovers were responsive to both Pathfinder and Mars Global Surveyor. Phoenix responded to observations made by orbiters. It showed there was frozen ground ice at high latitudes that it could go and study. Missions always use science that's been done to ask the next questions. I think it's perfectly possible that some subsequent mission would build on and maybe try to answer a more specific question that came out of the work that was done for Sample Return or even some of the previous missions.

ZIERLER: Now here I'll ask you to use your imagination because it's so far out into the future. But because there is some evidence, there is some suggestion of extant water below the surface on Mars, that there's water now, not just evidence of past water on the surface, but below the surface current water, could you see as the next mission, the follow-on mission to Mars Sample Return something that could get down to those levels where the possibility of extent water leading to extent life is theoretically much higher?

GOLOMBEK: First of all, there's lots of reasons to think that a subsurface liquid water environment could exist on Mars. I do not believe there is any compelling data to show that such a groundwater table does exist on Mars. There is compelling evidence that frozen water is in the polar caps and it's in the high latitudes. There's ground ice clearly at the high latitudes. We've seen that. Whether that also means that at much deeper levels, and the current—if you look at geothermal gradients for Mars, you would probably need to be going down a kilometer or more to get to putative, if it exists, liquid water environment down there. A kilometer deep is an extremely difficult place to get to, even on Earth where we have thousands of people on hand watching the drilling process as it occurs. Doing that remotely, it's hard to imagine. That would be extraordinarily difficult. Until there is compelling evidence that liquid water exists down there—and it's also the needle in the haystack. It's like looking for ancient life now. You could look in that haystack 1,000 times with your drill, and never find the needle. It doesn't mean the needle's not there, but it means that you're going to have a lot of missions with a sort of ill-fated or no result.

That's really why we're looking at the Noachian, the most ancient rocks on Mars, where we know the environment was already conducive to the formation of life, and it happened at a time when life got started here on Earth. Even if Perseverance does not find evidence for life, if it finds all the ingredients, and it finds all of these rocks, we will make thousands of discoveries that will spur on Mars science, regardless of that other question.

ZIERLER: Now, the capabilities of all of the Mars orbiters, all of the Mars landers, there isn't radar capability that give us some sense of where subsurface water might exist?

GOLOMBEK: There is a report for subsurface water based on some of the orbital radar in one of the polar caps, maybe that's beneath the ice of the south polar cap. But the interpretation of that data has been hotly argued as to how diagnostic and true it is. That's why I started that conversation with there's no unambiguous evidence that liquid water exists down there now.

ZIERLER: Another very future…I'll ask you to use your imagination again. Does Mars Sample Return get us closer to a human mission to Mars?

GOLOMBEK: Yes. In fact, one of the four primary goals for the Perseverance rover is helping to prepare for future human exploration. There have been myriad studies by NASA and others to talk about what sort of things you would like to do before you send people. There's a little bit of a bifurcation. If your intent is to send people to Mars to plant the flag, and say "we were there," and get back in their capsule, and come home, then you could argue how much previous information you really have to have. If your intent, however, is to set up shop on Mars, and have a habitat of some sort, then I think the answer to your question becomes much more like yes, because now you have to build habitats. You have to build places for the spacecraft to land. You need water. You need a place to go mine the ice to make water. You need things for the astronauts to study. I hope they send a geologist that can go do some geology. [laugh]

ZIERLER: [laugh]

GOLOMBEK: Now there's a much richer suite of questions, and facilities that you might need on the surface. The most recent NASA study has, yeah, they're setting up a habitat, and they have power sources, and they have roads, and they have a mining facility that makes ice and water for not only astronauts but to send the astronauts back home. If you're thinking of a scale of that, then you not only need Sample Return but I think you need rovers on the surface that scout out that landing site, or now it's this landing area, and make sure that you know that the environment is the way you want it. On Earth, you would never set up a mining operation from pictures from orbit. You also want to know how toxic the dust might be for the health of the astronauts and the operation of their life support systems.

You'd go down, and you'd burrow in the ground, and you'd make sure that the mineral or whatever it is you wanted was there, and you knew something about its concentration and so on. If you're thinking of staying, then, yes, I think you need both Sample Return to know about the toxicity of the materials that are there. Are there building materials? Can you make a habitat? Can you make structures out of that? Is there material you need that you want to harvest and do things with and so on? Then you need not only Sample Return, or rovers with ground-penetrating radar, and probably some ability to look down beneath the surface to find if the ice is really there. How pure is it? How much dirt does it have in it? How are you going to get it into liquid state so you can do something with it, that sort of thing?

ZIERLER: In the first scenario, minimally, what Mars Sample Return will do is show that going to Mars need not be a one-way ticket.

GOLOMBEK: Yeah.

ZIERLER: That's obviously important as a moral component. We would never send someone to Mars without the capability of bringing them back to Earth.

GOLOMBEK: It's a long trip. You can only go there and back every 26 months. You're talking about a three-year trip to get somebody there and back. It's nine months to get there. You're going to land them. They're going to stay for a little while. [laugh] Then it's nine months to get back. You're talking about something of the order of years. This is not like going to the Moon of a few days there and a day back or whatever, and you're done in a week. No. This is a major thing. You're off Earth for a really long time.

ZIERLER: Matt, let's go to some Mars landing decision 101. For you, who are the other experts in the room? Your expertise in geology and geophysics, who else is in the room where you're collectively making these all-important decisions about where to land?

GOLOMBEK: There's two big halves to landing site selection. The two big halves are science. What do you want to learn when you're there? The other half is engineering. If your spacecraft doesn't land successfully, it doesn't matter what wild things you might think you're going to get [laugh], if it doesn't land safely, you're not going to get them. [laugh] It doesn't matter what you say. Every piece of hardware that we build, each landing system has certain things that it's going to like, and certain things it's not going to like. There's engineering and there's science. We call engineering landing site constraints, if you will. Most spacecraft don't like meter-sized boulders that they have to land on or deal with. That's not a good surface. They don't like really steep cliff edges that they're going to bounce off of and fall down [laugh], so rocks and slopes. Material properties, you obviously want a surface that's hard and load-bearing. There are places on Mars where you might sink into what I call fufu dust, dust from the atmosphere that's not load-bearing. You'd sink right through it. You might be deep enough, you wouldn't see the spacecraft again. [laugh] That's not a good place to land. That's what you call engineering constraints, and it affects everything—everything. The elevation that you can go to is how much atmosphere you have above you. The lower elevation, you're going to have an easier time to land on than higher elevations. The top of Olympus Mons on Mars, you're not even off the aeroshell phase of landing. You can't land up there with current technology. It's not possible. You don't want to land at high elevations. You need all of that atmosphere. It's thin, but you use it, so you want to be as low as you can. Latitude matters a lot if you plan to use solar power. Even if you're not, it's a more moderate thermal environment if you're near the equator than if you're not.

If you want to launch something from the surface, you're going to definitely want to be near the equator because you're going to get a boost from the rotation of the planet to get your thing into orbit. There's a reason we launch spacecraft eastward, from Cape Canaveral, Florida. It's pointing with the rotation of the Earth, and it's over water, in case something goes wrong. You want to be as close to the equator as you can get to get the maximum push. [laugh] Same thing for getting your samples or anything back from wherever you are on Mars. Latitude, elevation, things you can't control are the atmospheric pressure changes by 25% seasonally on Mars. When you get there—and you don't have a choice in this matter, you can only go once every 26 months—you're going to get that atmosphere. If it's a bad opportunity, it's going to be thin. If it's good opportunity, it's going to be thicker. You get nothing to say about that. [laugh] Then of course there's rocks and slopes and so on. That's engineering.

But there's science too. Every mission has a suite of instruments. The mission has science objectives. The instruments have science objectives, things they want to study. If you want to look for life, you probably don't want to be on top of a layer of igneous basalt. That's probably not the right environment. Now you need a particular kind of rock. We talked about a delta for Perseverance, or water-related rocks, and things like that. Now you have this whole suite of not just the rocks, but is there stratigraphy, rocks and layers that you can relate to one another, and that you can relate to the overall geologic evolution of Mars? You generally have these two parts that kind of bounce together. [laugh] You want something that's safe, and something that will enable you to do the studies you want. Every single site selection has been different because every single mission has been different. Even when the spacecraft is almost the same, like Phoenix and InSight, what they were doing were entirely different, so where you sent them was entirely different.

ZIERLER: Matt, of course, it's not just Mars where JPL is playing a leading role in searching for life. There's the whole Icy Worlds program. Is this an asset for you, even if only you're an interested observer, to keep tabs on what those other missions are doing?

GOLOMBEK: Yes. There really hasn't been a mission to the surface of an icy body yet that would start to get that kind of surface information. But certainly it's tremendously interesting that there could be subsurface oceans on some of the Galilean moons around Jupiter or outer planet satellites. What they're talking about for those sorts of missions are interesting, but it's still pretty darn different from Mars. I mean, we're talking about ice, not rocks at the surface. [laugh] It's pretty different in that regard. I don't think the main tenets of any site selection that you were to do for any of those missions would be any different. It's going to be engineering. Can you land the thing safely, and can you do the science you want to do at that location? Those two things are going to be phrased in the same way, and they're going to have to come together in a site selection activity.

ZIERLER: If there is—

GOLOMBEK: Let me just go a little bit more on that. We have done site selections for, six missions since Pathfinder. With time, we've developed a process in which we have science conferences that are open for anyone in the world, anyone in the community, to come to these conferences, and give proposals about where to go with a mission, and why you would go there, typically focused mostly on the science. Then we down-select those prospective landing sites to start gathering the information that we need to evaluate a number of them in more detail. For Perseverance, the most recent, there were four of these landing site workshops. I'm a co-chair of the committee, the NASA committee that puts these things on. At the first one, we basically said, "Here's the latitude and longitude constraints. Here's the elevation constraints. Tell us where you want to go, and why it's important." Then there's a steering committee that would basically try, and we'd order those from the best-looking ones to the least good-looking ones.

We'd start getting images with our satellites that are in orbit, so mostly Mars Reconnaissance Orbiter, getting both mineralogical information as well as high-resolution images. The high-resolution images allow you to see whether, OK, are there rocks there? Is it smooth. Then you go through a process where you down-select. I think we went from 26. There were 30 sites that were proposed. Then we narrowed them down to like ten or something, and then we narrowed them down to four. When you get down to four, now you're making detailed maps of the surface. You're measuring the rocks, and how tall they are. [laugh] You're measuring the slopes to see whether this is an acceptable engineering location. You're also studying the area in much more detail scientifically, and you're even planning out potential traverses you might do with the rover. Then you get to a final workshop where you have four, and it's just about those four, and you hammer those four for three days until you get—effectively, I think the last one we voted, we asked everyone in the room to vote, and say not just which their favorite was but very specific questions about what made that site. Is it good for this? Is it good for that? We had like 12 or 16 questions. Then the steering committee got together and made a recommendation. Ultimately, NASA makes the final call, with input from the project. They have to enable this. There's this big process that takes as long as it takes to develop the spacecraft. It has to be done at the same time that you're engineering the spacecraft, because when you start thinking about the spacecraft, and when you've built it and designed it and tested it, those are not the same thing. There are often changes in the spacecraft as it's being built that you have to react to from the landing site point of view. It's uniquely a JPL kind of thing.

ZIERLER: [laugh]

GOLOMBEK: JPL has 95% engineers. Every type of engineer exists at JPL. There's not a kind of engineer that exists that is not at JPL—then they have a handful of us scientists that know something about Mars. You've got fuse these two things together. It's where the rubber meets the road. [laugh] It's where the airbags hit the surface. You can only do it at a place that builds that spacecraft, and has scientists that know something about what the surface of Mars looks like. It's the singular activity, if you will. I'm the only person that's done this for NASA, for Mars, since the modern era, since Pathfinder. There's only one of me. [laugh]

ZIERLER: [laugh] Matt, because you'll know what to look for, if there's a certain level of apprehension, that the political winds in Washington can change, NASA might make difference decisions with different leadership, what will you be looking for in terms of the budgetary environment, and in terms of how far along Mars Sample Return really is before you feel truly confident it's a go, it's happening? Are we there now, are we close, or is that some ways away?

GOLOMBEK: I think there's still work to do. There has been a report, and we know that NASA is looking at—so the program and the landers are in phase B, and it's been studied for a while, and they're moving along. But there is a re-architecture study that's going on now, because the program looks still more expensive than it originally looked to be. I don't think we're quite at the position we know for sure that it's all going to happen. I think we're closer than we've ever been. There have been at least two or three previous sample return studies that got kind of far within NASA and JPL, but never to this level. There's an agreement with the European Space Agency. They're doing part of it. There's multiple international things. I'd say we're closer than we've ever been before. Whether we're sure that it's all going to happen at this point, I'm not sure we're quite there yet. But we're, as I said, closer than we've ever been.

ZIERLER: You're feeling pretty good about it, all things being equal?

GOLOMBEK: Yeah. We're studying places to land the Sample Retrieval Lander. That's what I'm doing now [laugh] is trying to find the location to land the lander, such that the Perseverance rover can meet it, and deposit the samples. There's a site selection. We know it's going to be somewhere around Jezero crater or nearby. But you still have to pick the site, and you have to certify that it meets the objectives that you have in mind. That's already going on.

ZIERLER: Matt, let's go back. Let's establish some personal history. As an undergraduate, you're already interested in geology. Were you interested in non-terrestrial geology, even at Rutgers, or that came later on?

GOLOMBEK: I think when I was an undergraduate, there probably wasn't—maybe there was a—I don't know if there was even a career called planetary geology. [laugh]

ZIERLER: You graduated before the launch of Voyager.

GOLOMBEK: Yeah. I didn't know that there was a career there. I was interested in it. It seemed interesting. I certainly was very interested in geology. My undergraduate major was in geology. I think I took one class that was available at my undergraduate institution, which was mostly about meteorites. It was pretty basic. I said I was interested, as I was graduating and went to grad school, in structural geology and planetary geology. I went to a location where I did both of those for my graduate career. By that time, the Viking data was back, and there was a career there. I didn't know if I was going to be for sure into it. It wasn't a very robust environment yet. It was pretty much the doldrums from Viking onward. If you weren't on the Voyager missions, there wasn't a lot of support. It wasn't a very big field. I didn't know where I was going to end up after that. After my PhD, I got a postdoc at the Lunar and Planetary Institute in Houston, which is right next to Johnson Space Center. I did that for two years. That's pretty standard for PhDs that are interested in academia, and that's what I am, an academic. Then JPL offered me a job, and I accepted it, and I've been there ever since.

ZIERLER: Tell me about the geology/geophysics program at the University of Massachusetts.

GOLOMBEK: I was very fortunate to work with two structural geologists at UMass that were also in the space program, and they worked on both the Moon and Mars, and I had the ability to work with them. There was also a geophysicist there that did paleomagnetism, and I did some of that as well. I really got pretty broad exposure to a bunch of different topics and things that were interesting back then. It was a good starting place.

ZIERLER: What did you focus on for your dissertation?

GOLOMBEK: It was very interesting. This is a little bit of history here.

ZIERLER: Please.

GOLOMBEK: My master's degree was on lunar grabens, which are fault-bounded valleys on the Moon. When I finished that, and I was deciding about a PhD topic, both of my advisors said, "There's not a whole lot happening in planetary right now. You might want to make sure that you're doing something in terrestrial science so that, if you needed to, you could get a job." The dominant jobs, of course, are in the oil business. At that time, at the University of Massachusetts, just about every major oil company came at about graduation time, and hired just about anybody who was interested in working in the oil patch. They all got jobs. This was almost like a feeder program. If you were interested in going into oil and gas geology, you could get a job by having a master's or a PhD. My advisors said, "If nothing else happens in the planetary program, you at least will be employed in oil when you get done with your PhD." [laugh] I did a terrestrial PhD. It was a mapping thesis. It had nothing to do with planetary science whatsoever. But I was still interested, and I did some stuff on the side that was planetary.

When I finished, it was the year before the gas shortage? The gasoline—there was not enough gas, and people were in lines. The oil business stopped hiring geologists the year before I finished. There were no geology jobs. In fact, there haven't been any geology jobs since, really, because it's all chemists and engineers. They already know where the oil is. It's just getting it out. [laugh] There's not so much in the way of geology that's going out at the oil business, so there were no jobs available. [laugh] I was all ready if I needed to get a job, although I don't think my heart would've been in it. I took a postdoc that was more towards planetary.

ZIERLER: Matt, the road not traveled, had you gone on, if you could extrapolate your dissertation research, and that would've become an academic career, what would that research have looked like?

GOLOMBEK: I would've been a structural geologist in both Earth and planetary science, and I would've been just like any academician at some university, writing proposals and doing research on that.

ZIERLER: Have you followed the research at all? Have you followed what you worked on, where that's gone?

GOLOMBEK: I'm not a structural geologist anymore, and I haven't been for a really long time. I'm a Martian now. [laugh] I only work on Mars, and I don't do things that are structurally or geology related. I don't do anything that was related to my dissertation. I've reinvented myself several times since then. [laugh]

ZIERLER: Is there any such thing as structural geology on Mars?

GOLOMBEK: Oh yes, and when I first started, I did do that. In fact, I wrote a whole slew of papers about the structural geology of Mars, Mars tectonics. I wrote the last review paper on that topic. It's in a book somewhere that you could fall asleep reading. [laugh] I'm still quite knowledgeable about it, but I don't actively do research on it anymore. My research focus has changed, with a lot having to do with what I spend most of my time, which is looking for landing sites, and that's looking at remote sensing data, and relating it to ground truth. That's what you're doing when you're looking for a landing site. You're predicting, if you will, what the surface is going to look like before you get there. If you think about it, there's not a lot of fields in planetary geology where you get to see if you were right in your lifetime, maybe ever. [laugh] You might write a paper about something that will never be tested. But I write a paper before we land that says, "Here's how we found this site, and here's what is going to look like." After we land, I say, "Did I get it right or did I not? [laugh] How did I screw up?" [laugh] That's kind of cool, right? Now I've done this seven or eight times.

ZIERLER: Now, Matt, in choosing your postdoc, were you self-consciously pivoting toward planetary science at that point? Did you recognize this is where you were headed?

GOLOMBEK: No. All of the postdocs that I considered seriously, I was going to do both planetary geology and Earth geology. The one I picked had that capability as well. In fact, when I was at LPI, Lunar and Planetary Institute, there was what they were calling a rift initiative. They had this initiative to study continental rifts. That was a big topic of study back then, and I was participating in that with a whole bunch of geochemists and geophysicists, and it was a wonderful environment to be part of. I wrote all sorts of papers about the Rio Grande rift. That's where I did my dissertation. I was following that trajectory, as an academic geologist would. It wasn't until I got to JPL and really started working on missions that I sort of changed, and stopped doing that research, and started doing things that were more related to this relation of orbital data to surface data. That's really what my expertise is now.

ZIERLER: Matt, do you have a sense of the origin story of the Lunar and Planetary Institute, how it got started, and why Houston?

GOLOMBEK: Yeah. It was started, in fact, it was originally called the—it was the first workshop after the Apollo, the first Apollo science conference, and they brought back the rocks. They had a workshop to talk about scientifically what were those rocks? They wanted an independent institute from Johnson Space Center, which was the doing organization that would be more like a think tank. Originally it was called the Lunar Science Institute, and then they broadened things out to Lunar and Planetary Science Institute. It's basically supported by NASA. What it does now mostly is support conferences and workshops and things like that. They do have a small science staff as well to help with that activity. It's not a very big place; maybe 30, 40 people, kind of thing, maybe 50 people. But when I was there, it was a rich environment to develop.

ZIERLER: Is there an advocacy component to LPI like there is with the Planetary Society?

GOLOMBEK: No, because if you're NASA, you don't do that. [laugh]

ZIERLER: Right. [laugh]

GOLOMBEK: You're the doing organization. [laugh]

ZIERLER: You're not advocating the mothership, so to speak?

GOLOMBEK: Just like JPL doesn't, or any of the other NASA centers. NASA itself can, but it typically does that through National Academy of Sciences, that sort of thing.

ZIERLER: Now, what was your original connecting point to JPL?

GOLOMBEK: When I was at LPI, I was on a committee called the Cartography and Mapping Committee, which was a committee that NASA did to make sure that the maps that were being made for the planets were helping the scientific community. I'm guessing that still exists somewhere. But they basically look at the cartography program, which is done dominantly at the US Geological Survey in Flagstaff. They were the ones that made these quadrangle maps for Mars, and they made the base maps for Mars and the Moon. There was this science group that would look at what they were doing, and offer opinions and ideas about how to improve things. One of the other members was a scientist at JPL, and I interacted with him for probably a year or so. As my postdoc was ending, he said, "You really ought to think about JPL. You would do well at JPL." They invited me out for an interview, and I interviewed, and I eventually came.

ZIERLER: What were your early impressions when you arrived at JPL? Was it exciting? Did it immediately strike you as the place to be?

GOLOMBEK: I'd been at JPL prior. A professor I worked with was a guest investigator on the Viking Extended Mission. They sent me out to JPL to get some maps and get some of the data that we needed to do the kind of science we wanted to do, while I was a grad student. I had already been at JPL, and I was in the Viking operations area while it was occurring. It was pretty sleepy by the time I got there, because it was just the orbiters by then. But you could talk directly to the engineers, and then the images would come down as they would take them. I'd say, "I'm really interested in this area," and then you start getting pictures. That was pretty cool. It's always neat to be at the place where, you know, that's where it's really happening. [laugh]

ZIERLER: What year did you arrive at JPL? Was it '83, '84?

GOLOMBEK: '83, yeah. I'm just in my 40th year here. [laugh]

ZIERLER: Wow.

GOLOMBEK: I keep saying "it's only" because I probably had four or five different careers within that, where I did different things that—

ZIERLER: Keeps it fresh.

GOLOMBEK: Yeah, and it allowed that flexibility, if you will, that I could change from being a project scientist and I was the project scientist on Pathfinder. That's dominantly a management job. You're generally not doing a lot of science. You're making sure all the pieces are working in the right order. When I got done with that, I decided I didn't really want to do that; that I really wanted to go back to doing research. I had to change my trajectory [laugh], and I've had to do that a bunch of times. But JPL's always had enough opportunity to—and, at least for me, I've been able to find initiatives that I've been happy with.

ZIERLER: Just looking at the chronology, you start in '83. Mars Pathfinder lands in '97.

GOLOMBEK: Yeah.

ZIERLER: Is it all Mars for you, right from the beginning? Is there a viable Mars Rover program?

GOLOMBEK: There was no Mars there. Viking was dead. There were 20 years between Viking and the next mission. In fact, it was the doldrums of the planetary program. There was nothing happening whatsoever.

ZIERLER: In your first decade, what did you do? What did you work on?

GOLOMBEK: I did science. I just worked on a whole variety of science topics. I was involved in some of the early measurement of plate motions of VLBI and GPS measurements, where we were measuring. I've got a bunch of papers that I did about that. I worked with a whole bunch of different planetary people. Eventually, I started working on advanced studies for Mars that were ideas about what you could do, but none of them ever happened. They were all just viewgraphs. Then Pathfinder came along, and it was like, oh my god, this is the real mission. [laugh] We can do something with it. [laugh] We can go to Mars, and get some fresh new data. That was tremendously interesting. I call myself the oldest Martian.

ZIERLER: [laugh]

GOLOMBEK: Since 1993, I've worked on nothing but Mars. If it's not Mars, I don't do it. You can only do that if there's enough work to support you. I don't know if there's another scientist that started doing that continuously for longer than me. [laugh]

ZIERLER: For your first decade, just doing planetary science, was Caltech an asset to you? Did you work with Caltech faculty at all?

GOLOMBEK: No, not back then.

ZIERLER: Was that not in JPL's culture?

GOLOMBEK: It wasn't in Caltech's culture.

ZIERLER: Interesting, interesting.

ZIERLER: Was this irksome to you? Were there opportunities to change the equation?

GOLOMBEK: They tried. There was one time, there were a couple of years where all of the incoming grad students would come and talk to some of the JPLers about, but none of them could work with you [laugh] because they weren't a Caltech prof. It has changed, and it's changed for the better.

ZIERLER: That's good to hear.

GOLOMBEK: I'm a visiting associate at the geology and planetary division now, and have been for over 10 years, and I've worked with a handful of the faculty and written papers with them, and it's been nothing but good. Nothing bad to say. But I think there was a real cultural change in the view and the interaction, and there's a lot more going on now than there had been then. I taught a class at Caltech when they were changing faculty. They wanted the planetary surfaces graduate course taught, and they asked me to teach it, and I was thrilled to teach it. I had an office down there, and I interacted with a lot of faculty. I have nothing but good things to say. They have great people, and they're pretty open. But it takes—how do I put this? You need a reason to be interacting—it's an organic thing to interact scientifically. You're working on something, and they know something about it, and you start working together, and that's what drives it, really.

ZIERLER: Given that this has shifted, and it's for the better, to the mutual benefit of Caltech and JPL, are there any heroes in this story that you can point to that fostered this relationship? Is it a division chair, JPL director, Caltech president that sticks out in your memory?

GOLOMBEK: I think a lot of it has to do with the attitude of the division. That's my personal view. I think a lot more of the faculty are involved in missions as actual co-investigators on the missions. I think they're much more aware of the kind of work that happens at JPL, and how honestly special it is. I think they've looked at the talent that we have at JPL, and they recognize that there's nothing bad about having that involvement. I think the involvement's been much, much better, and I've been pleased as punch to be able to work with the faculty at Caltech in the last probably 10, even 12 years.

ZIERLER: Now, did you wake up one day, and learn about the Pathfinder mission?

GOLOMBEK: [laugh]

ZIERLER: Were you involved in sort of the iterations, the early iterations of the program?

GOLOMBEK: As I said, there were these studies that were happening, and they were on all sorts of things, and I was like the study scientist that was helping the engineers. At some point, there was a study called a Network Mission to Mars, which was called MESUR Network. The idea was to put down 12 surface landers that did seismology, and atmospheric science, and a little bit of geology. The idea is that you can use the seismic waves to understand about the interior, and these atmospheric stations would allow you to understand about the atmosphere and so on. It was studied for a series of years. When the price tag came out, it came out to the $1B, number, B being billion, and that was far too much. The thing kind of got semi-canceled. But then there was this idea that there was this Pathfinder, which would be the single first demonstration that you could put a small, inexpensive lander on the surface of Mars, and do something useful. It was designed as a tech demo, a technology demonstration, so not really a science mission. The idea was to demonstrate a low-cost landing system. At the time, all JPL missions were these Galileos, and these big, expensive multi-billion-dollar with 20 instruments on them, and they're complex, and they're expensive, and they take forever. The idea was, back then, the NASA administrator was Dan Goldin, and he wanted something faster, better, and cheaper. I was the study scientist on MESUR. When the one billion dollar number came out, that seemed too much. At the same time, JPL was working on initial mobility concepts, and they had a thing called—I've forgot what the rover was, but it was this giant rover. It was bigger than your car. Maybe it had pods or something. But it had this big, giant computer on it, right, like a full mainframe. Back then, that's the only—this is before laptops. [laugh] There were no personal computers. [laugh] It's hard to believe. There were just these mainframes. They had a mainframe on the thing. That's this big, giant computer. Now you need an air conditioning system or a heating system, because computers like constant temperature. [laugh] Now you have this big thing around the computer to keep it happy. Now you've got this big spacecraft, so it needs big wheels. The thing was this giant.

Of course, when you got around to thinking about sending it anywhere, you needed this big launch vehicle, and that means you needed a lot of money. It was drowning in the weight and the mass. It was just at the start of the computers. There were chips. There was a fantastic JPL engineer that figured out that you could do things that were more like reactionary, so like a fly. A fly has built into its brain that it cannot flap its wings until it jumps off the surface, because its wings are long enough, they would break against the surface if it flapped. This is an and/or switch. Do not flap wings until you've jumped off the surface. [laugh] They figured out that you could string a bunch of these and/ors together, and you could have a rover that would move itself around. Charles Elachi, who was then an assistant lab director—not the director—decided that we should do a demonstration of this microrover. I was the study scientist to help that. We built this little, microrover. It was as big as like your printer or something. It was less than a microwave oven. It drove around. It did a few little things. Everybody's like, "Wow, this is pretty cool." Pathfinder was the tech demo with a little microrover. That was the key. A microrover is going to prove that mobility was useful on Mars. At the time, a lot of the geochemists were just saying, "We don't care what kind of rocks we get from Mars. Just land, get me a scoop of dirt, and I'll tell you more about the solar system than all the images in the world"—some of those were at Caltech, by the way. [laugh] "We don't care where. Just bring it back." [laugh] Most of us geologists thought that, gee, this makes a little more sense if you can rove around, and pick up the right rocks [laugh], and not just any old rock, and not just the dirt, and so on. [laugh] That was the beginning of Pathfinder, and because I had worked on all of the things that had come before it, I was sort of the natural to become the project scientist.

ZIERLER: How did you shift to all of those administrative, managerial responsibilities?

GOLOMBEK: First of all, let me tell you a little bit more interesting story—when I accepted the project scientist job, most of my academic colleagues—actually, not most of them. But some of them said, "What are you doing? You're throwing away your science career, working on a tech demo that has no science. That's not what NASA should be doing. You're wasting resources, and you're wasting your time, and this is going to kill your career." [laugh] My thought was, "Here's an opportunity to get some new Mars science." Even if it's a small first step, it's something that you can do to show that there's a utility of this sort of exploration. I don't think I have to argue with you now that if there hadn't been a Pathfinder, there would not be a MER, a Mars Exploration Rover. If there had not been a MER, there wouldn't be a Curiosity or a Perseverance. It all started with Pathfinder, and you got to take that first step. Being a project scientist is a full-time job, and it's all immediate, and there's "fire drills" every single day, and you have to be involved in them. You just don't have time to write papers, or even to sit down and think critically about what you would do writing a science paper. It's just not something you could do. Five, six years I was pretty much a project scientist. At the end of it, I made a conscious decision that I wanted to be a research scientist again. I just didn't really want to go into management. That was among the hardest transitions, because all your grants had lapsed, so all of my grants that I had that were supporting me. JPL's a soft money environment. If I don't bring in money, I'm unemployed. All of a sudden, I had to transition. I had to rewrite those proposals. I had this transition period where I had to redo all of that. That was one of those career changes. [laugh] That was my third change, if you will. [laugh] But it was a good one.

ZIERLER: Tell me about the launch.

GOLOMBEK: Since then, I've been a research scientist. I publish papers. I write.

ZIERLER: You did it. You did it.

GOLOMBEK: [laugh] I love doing that. [laugh]

ZIERLER: Matt, tell me about the launch of Pathfinder. What was that like for you?

GOLOMBEK: There's two points for a space mission that are pretty definitive. The first one is the launch, and the second one's the landing. [laugh] The Pathfinder launch was on a Delta II rocket with solid rocket boosters. Six of the boosters are ground-lit, and three are air-lit. Of course, you know all this in detail because you're having the thing built. I remember it was at two in the morning, and it has a one-second window on Earth. It could only launch at one second per 24 hours on Earth. The first night, I think it rained out or something, and maybe even the second. But the second or third, it was clear. We got up at two in the morning, and you're there. It's the middle of the night. You're groggy. You watch the thing go up. The whole time, you're going, "Let it go safely." [laugh] I remember counting the solid rocket boosters, the six that fell off, and then counting the three air-lit ones, just like, "OK, did that go all right? [laugh] It launched fine. It had a bit of trouble in cruise. Let's see if I can remember the story. We almost lost the spacecraft. The final, the third stage, when it fired, put soot on the Sun sensor. The spacecraft couldn't figure out where it was. It couldn't get attitude control. They turned it on, and the thing can't lock onto anything. They eventually troubleshooted and figured it out. It turned out that several of the sensors on the Sun sensor were not occluded. They figured out how to just train the algorithm to use those in order to get attitude control. If you don't have attitude control, you can't do the trajectory correction maneuvers, and you can't get to Mars.

When you launch to Mars, you don't launch at Mars. Your trajectory is biased, in case you lose the spacecraft, because you don't want it hitting Mars with all the dirty stuff around it. You're biased away from Mars. Then, of course, landing is the 6 or 10 minutes of terror. Of course, we'd never landed with airbags before. We'd never done anything this crazy before. The whole project cost—the lander was $150 million. The rover was $12 million. The launch vehicle was $40 or $50 million. The whole thing cost less than the movie Waterworld that you never saw. We were going to Mars, and we were going to do some science. [laugh] That was a tremendous opportunity. Of course, the public reaction was—none of us, no one was prepared for that reaction—I'm trying to think of a mission that the public got as involved in. Back then, before the internet, we were on the front page of every national paper for a week—a week. At the time, it was the beginning of the internet. It was the largest internet event in history. People were enthralled that this little rover could go out, and they could see it move, or move from one place to the other. They were completely involved in it. It was amazing. [laugh] It was amazing. We were NASA heroes. [laugh]

ZIERLER: You were planning. You knew you wanted to go back to science, even amid this success.

GOLOMBEK: That was the public success. I could have gone into something totally outside of science as well. [laugh] But, no, I didn't really want to do that. But that all died down after a while. Usually that kind of thing does. I got to write a book from it. I consciously made the decision I wanted to be a research scientist.

ZIERLER: Tell me about the book.

GOLOMBEK: It's a National Geographic book. It came out the year later. I was also the science advisory for a couple of movies with Hollywood. It was fun. [laugh] Invited to speak all over. Members from the project were invited to speak at all sorts of events.

ZIERLER: Matt, after all this success, tell me, either in your direct participation or just being around the failures of Mars Climate Orbiter, Mars Polar Lander, what did that mean for you? What did it mean for Mars science? What did it mean for JPL?

GOLOMBEK: If Pathfinder was the crowning success of "faster, better, cheaper," Polar Lander and Climate Orbiter were the depths of despair. All it takes is one thing to go wrong on a spacecraft. There was at least one thing that went wrong on both of those. In both cases, a more robust engineering team probably would've caught it, or could've caught it, or might've caught it. They were just stretched so thin that they couldn't find it. Me personally, I didn't work on either of those, so it didn't really affect me too much. It was certainly a blow to JPL. But JPL had lost Mars Observer before Pathfinder. Remember, that was an orbiter. I was a participating scientist on that mission, and that was a loss, for sure. I think that was more towards the idea of smaller, more focused spacecraft. Instead of having these big, giant things with a lot of instruments, make them smaller and focused. What came out of Mars Observer was Mars Global Surveyor, which was a slimmed down payload from what was on Mars Observer. That was fantastically successful, but with fewer instruments and, again, more specific. That's the way the missions then went. They were not these big, giant things. They were much more cost-constrained, which was in the fiscal environment at that time.

ZIERLER: Now between '98 and 2002, when you join MER, are you doing science that's not attached to a mission?

GOLOMBEK: Yeah. That was me getting back to being a research scientist. I was still doing some structural geology on Mars then. [laugh] But I was involved in MER from the very beginning. As soon as it got the start, I became the landing site scientist on it. At that time, I was not part of the science team, because that was a science team that was selected from a proposal that was written that was smaller. But I worked for three years prior to the mission launching, during development on the landing sites and the landing site selection. I worked on that, and then I became a participating scientist on MER, and then in fact became the project scientist. I was the last project scientist that lasted. In fact, I served the longest. I think it was seven years. But that opportunity lasted 15 years. That was a big chunk of my career was working on those two rovers. Geez, I published scores of papers, and I had so much fun. [laugh] I had so much fun.

ZIERLER: But did you go back on your vow never to do that level of administrative work again?

GOLOMBEK: No, it wasn't administration, see. First of all, I was originally a participating scientist. I was a co-investigator. My job was to do science. I did other things as well. I planned the pathways from the original landing site to Victoria crater, and from Victoria crater to Endeavour crater. But that was science. By the time I became project scientist, it was a quarter-time job, and not a full-time job. It was a little bit maybe of administration, but I could still do a lot of science. [laugh] Of course, I obviously knew how to do the job. [laugh]

ZIERLER: Matt, to go back to the friends who were concerned that you were throwing your career away, during a technology demonstration with Pathfinder, at what point in your involvement with MER did you feel great that, no, Pathfinder was the first step to doing science? What did that look like for you?

GOLOMBEK: I had to write a proposal to be a participating scientist. I was a member of the science team, and I just threw myself into them. They were tremendous missions. It was so easy to carve out and do science, and to affect where the rover went. It's so much fun. It's like being on Mars. [laugh] You get the data in the morning and You look at it. You have two hours to decide what to do next with the rover, and then you have the whole day to put the plan together. Not only was I a SOWG, Science Operations Working Group Chair, I was in the ops room with them as we were developing the plan. I did that for 10 years or so. The data comes in, and you're like among the first people to ever see this place on Mars. Then you have to decide what to do next. What do I see here that tells me? Is there a rock that we ought to go look at it? Then you had to meet with the science team, and you had to come to consensus about what to do, and then you had to put the plan together to do it. It's just like being on Mars. I was on Mars. This idea that you have to have a human being on the surface of Mars to experience it? There's dozens, maybe hundreds of people at JPL that are on Mars. They live on Mars. They operate a spacecraft on Mars. Your consciousness is on Mars. You're on Mars. [laugh] Now, it's still a baby step. I'm sure it's different if you were actually there. [laugh] But you're there. You're on Mars. That's the closest thing as you can get to being on Mars till we are on Mars. [laugh]

ZIERLER: Matt, how did you become the landing site guy? How did that happen?

GOLOMBEK: I was the project scientist for Pathfinder, and finding a landing site was something that needed to be done. The project had to figure out where we were going to land. That was a tremendously interesting science thing you had to do? Where are you going to send it, and why are you going to send it there, and what are you going to do that's going to make it interesting? That was fun because you've got the whole planet. [laugh] Where are you going to go and why? What can you do with the microrover with an APXS that would enable you to find the most out about Mars? Remember, at that time, only Viking had been there. We had these Martian meteorites, so we figured there were these big basalt volcanoes, so we thought there was some basalt. But we didn't know if there were any other kind of rock types. We didn't know anything. [laugh] That was this tremendously interesting kind of science activity that was part of it. I took that on. I said, "This is fun." I ran the site selection. I was inside the project and outside. We even had outside workshops—I went to LPI, and I said, "We ought to really do a workshop on this." We did two LPI workshops. That was just me saying, "We ought to involve the science community in this." It was really fun. When we got around to the next mission it became very clear that what I had learned from doing Pathfinder was a recipe, and that there weren't a lot of other people that knew about this recipe. In fact, there was just me or a couple of us. I said, gee, what if I help the project? I'm at JPL. They know me. This is a good thing. JPL needs somebody to do this. If you have spacecraft going to Mars, it'd be good to have somebody that knew where to send them. [laugh] This is a growth field. [laugh] I figured out a way to become the landing site scientist for MER. Then it was like all the engineers, every time a mission came along, they said, "Got to get Golombek. That's the guy. He knows how to"—[laugh]. I just became a success. My success bred more success. [laugh]

ZIERLER: Do you have insight as to why there were two rovers, why Spirit and Opportunity?

GOLOMBEK: Oh yeah. It was NASA Headquarters that suggested, first of all, the opportunity that MER was going was incredibly advantageous. In other words, when you got to Mars it was near the peak in the atmospheric density. You could land more mass at the same elevation than you could if you got there when the atmosphere was thinner. It was a prime opportunity to send a spacecraft, and everybody knew, even from the beginning, that taking a Pathfinder rover, and sticking it inside this tetrahedron was going to be intensive and difficult to do. Mass is always a problem. These spacecraft, both of them, had to go on the same Delta II rocket that Pathfinder went on, which had a fixed size of the shroud, so you can't make it any bigger, and it only has a certain amount of mass that you can throw to Mars. You were constrained from the beginning. I think there was concern that if one failed, it would be a pretty negative look on the Mars program overall. The suggestion, I think it was at Headquarters. It probably was Ed Weiler at that point—he would've been the head of the Office of Space Science—saying, "Maybe you should send two, so if one of them fails, you can still claim success." Interestingly enough, when you build two, there's advantages to just building one, because you can test different things on different spacecraft, and you can optimize that testing for where they are in the clean room in the assembly rooms at JPL. The engineers loved it. They thought it was great. But it was a crunch. It was three years to build both of those. Pathfinder was three years, which was the fastest anybody had ever done something to Mars. I think MER was even a few months less than that. Of course, the launch date is an absolute. "The dog ate my homework" is not an excuse. It's either ready to go on that rocket, and you have full confidence that it's ready to go.

ZIERLER: How much science were Spirit and Opportunity designed to do?

GOLOMBEK: A ton. they were designed to be geological explorers. It's interesting, I didn't recognize it at the time. For me, they were the best, because they did things that were almost like field geology. You didn't have super sophisticated in situ instruments, but they were sophisticated enough to get at rock chemistry and rock mineralogy, and you could see high-resolution images. But you didn't need to spend weeks coring, and breaking it up, and sticking it into this laboratory, and sitting around and waiting, like Curiosity did. Curiosity, in many ways, is driven by those laboratory instruments, just in the same way that Perseverance is driven by getting those cores. Because so much of the spacecraft was built towards sampling, it had to spend a lot of time and energy on that. But the MERs, it was like Discovery. You'd go, and you'd see things, and you'd decide what to do, and then you did them, and you did them in a fairly short period of time, and then you went on to the next thing. The ability to cover—what did we do?—20 kilometers, more than that, with Opportunity over 10 years, and discover that suite of things, I don't know if that'll ever happen again. [laugh] For me, it was the surface geology, and how did those landforms get to be that way? How did they relate to the orbital imaging? I learned so much that helped me do the next landing site selection for Mars Science Laboratory for Curiosity from that experience of relating where we went with the rover to what we saw from orbit. It was like each time we drove, we drove to a new place. I'd say, "Did I recognize that in the orbital images? Did I get it right? Did I see that connection? What's dangerous; what's not?"

ZIERLER: At a certain point, were you dual-hatted with MSL, or that was just adjacent to what you were doing?

GOLOMBEK: It's a funny story. Yes, I was dual hatted, so I was doing site selection for MSL while we were still operating the rovers. But I wasn't full-time on it, I was just part-time, and so I was probably—I don't know—quarter- or half-time on MSL, and quarter-time on MER. I had something else that was going on. But that's the way scientists are at JPL. You mix. Right now, I'm part-time on Sample Return landing sites. I'm on the helicopter, finding airfields for it to land again. [laugh] I'm still doing InSight science. I was the landing site lead for InSight, and the geology lead for that mission. That just ended, but I'm still doing some of the science for that. You always have these different things you're doing at the sort of same time.

ZIERLER: Was there ever discussion about a helicopter for Curiosity?

GOLOMBEK: Not that I remember.

ZIERLER: Because that was just too crazy, it was too far out?

GOLOMBEK: The technology and the idea to do a helicopter in Mars's atmosphere didn't come along until—I can tell you when it came along, exactly, because I was the PI of the proposal that proposed the helicopter. [laugh] It was just before the proposals were due for the instruments on Perseverance. The mission had been in phase A, and it was going forward, but it hadn't done the instrument selection yet. What NASA does is they put out an announcement of opportunity that says, "We're going to fund these kind of instruments that do these sorts of science. You propose an instrument, and if you're accepted, you're put on the team, and you're put on the project."

We, JPL—I was the PI—proposed the helicopter to assist, to be a scout for the rover to map out areas. Although we have high-resolution images, they're not quite at the resolution that you can see individual outcrops and/or places that you might want to go and study with a rover. The proposal was to use the images from this aerial platform, and fly out, and get a more regional view of the geologic units, and help decide where to send the rover, and even to help drive it there more quickly. The proposal was not selected, but it was interesting enough to both JPL and NASA that it became this little add-on, again, technology demonstration [laugh] that got on the space…now, in this case, I went from PI to nothing, because it became just a tech demo, and there's no science. I had no role. Here's a case where helping in the beginning didn't help me much at the end. [laugh]

ZIERLER: Did you see Curiosity as an evolution in capabilities and in science from Spirit and Opportunity—

GOLOMBEK: Oh yeah.

ZIERLER: —or was it something different?

GOLOMBEK: No, definitely it was an evolution, and the idea was to get at more definitive mineralogy. Geologists study rocks. Rocks are made of minerals. That's our currency. If you can identify the minerals, you can identify the rock. If you can identify the rock, you know how it formed, and you know the environment it formed in. Was it liquid magma that solidified? Was it laid down in water? That's what geologists do. Show me a rock, and I can tell you how it got there. [laugh] But we only got iron mineralogy from MER, and we got geochemistry. Now, chemistry's nice, but it doesn't tell you how those elements are arranged into minerals. What we really want is the minerals. We like the chemistry too. That's also interesting. What Curiosity was designed to do was to get definitive mineralogy, where you're measuring the minerals directly. They had two instruments that enabled it to do that, but it required them to get samples, and core the rock, and get comminuted samples that they put in those instruments.

They did a lot of chemistry too and other things. That was the evolution from like a field geologist looking at the rock. It's kind of a basalt. I can maybe see some crystals and pieces. I get the chemistry and, yeah, it looks like a basalt, to, oh, I know this is a basalt, and it's got calcium, pyroxene, and yada, yada, yada, everything, all the details in it. That was the change. Then the success of that really led to Perseverance, which is, we know there's habitable environments. Can we get those samples that we eventually might bring back to Earth that would enable us to start answering the questions that we started this conversation about whether there was life that got started there.

ZIERLER: Now where does InSight fit into all of this?

GOLOMBEK: It was not in the Mars program. InSight was a NASA Discovery program mission, and kind of a funny story. At the end of Curiosity—I can tell you this because you're asking, you're interviewing me. [laugh] At the end of Curiosity, we had done the landing site selection. I was not in the science team for Curiosity, so I was done. I'm looking around, and I'm going, "I've got no more landing sites." I'm out of business. I've got nothing to do here. I'm trained to be this expert site selector, and I've got no sites to select. [laugh] I needed a mission to select a landing site. I had been a co-investigator on a number of previous Discovery missions that had proposed a single lander on Mars, which was dominated by a seismometer with Bruce Banerdt of JPL, who's the PI of the mission. I knew he was studying, and thinking about sending it in again for the next Discovery call.

ZIERLER: Matt, was there reason to believe that Mars was seismically active? What was the reasoning behind the seismometer?

GOLOMBEK: Yeah, I wrote a paper about that as a structural geologist [laugh] in 1990. I think it's 1990; maybe even before. I wrote a paper that predicted the seismicity of Mars. It was based on the structures you could see at the surface, and the slip that had occurred, and the time in which the slip had occurred. We did a whole bunch of stuff to show that it was likely. But the most cogent argument for why Mars would be seismically active— and this, by the way, your question was not unusual. All sorts of people said this. "Why are you going to send a seismometer to Mars if you don't even know that there's Mars quakes? You're not going to measure it. It's a silly thing." We had two places where we had measured earthquakes: the Earth and the Moon. On the earth, super active tectonics, quakes happening all the time, I mean, all the time. The Moon was reasonably active, and there were tectonic quakes that occurred, even though not much geology has happened in the last three billion years. Basically, what we said is Mars is going to be in between. It's not as geologically active as the Earth, so it won't be that active. But it's had geologic activity throughout time from basically the oldest rocks on the surface you can see are probably four billion years and there are lava flows on the surface that are two million years old. Mars has been active throughout solar system history. There has to be tectonically active. This planet has to be having both tectonic activity and quakes commensurate with its geologic activity that's somewhere between the Earth and Moon. We estimated the total number. By the way, that estimate is pretty damn close to what InSight has found. [laugh] Of course there's going to be Mars quakes. There's no question here. [laugh] That was used as part of the proposal.

Anyway, I talked to Bruce, and I said, "Are you going to submit this proposal again?" He goes, "Yes." I said, "Do you think you have a role for me?" He goes, "I don't think you're going to be interested in this mission. It's just a seismometer." I said, "You still need a landing site, don't you?" He goes, "Yes." I say, "I'm your guy. [laugh] I can find you a landing site. Make me a Co-I and I'll run the landing site program for you." This was just me to get some more work. [laugh] I was interested in the mission as well, so I did that, and the mission was successful. It won the competition, and it's incredible competition to win a Discovery mission, because you go from the proposal to a thing where you have a NASA visit with this review panel of 50 people that ask you questions before they do the down-selection. We won this, we got it, we're on it, and now I had some work. [laugh] I had a site to go find. At the same time, they decided that they were going to do Perseverance. Now I had two landing sites to find. Those site selections went on at the same time. I was doing two of them at the same time. [laugh]

ZIERLER: Were they mutually reinforcing? Was involvement in one beneficial to the other?

GOLOMBEK: No, not so much, because the science that they were doing was so different. Now, some of the tools that we used on the characterization side were beneficial. It's a little more involved. But the way we learned to map the rock distributions on Mars, measuring the shadows from the rocks in high-resolution images, we made some advancements that helped us for both of the subsequent selections. There were things that peripherally helped, but the science was so different. InSight didn't care where it landed, as long as it was safe and flat, and it was safe to put the instruments down. It didn't matter what kind of rocks were there. It was looking for marsquakes. The surface geology had nothing to do with it. Perseverance is all about surface geology. That's the most important thing. [laugh] They didn't care about a marsquake. [laugh] No, they were pretty disparate and different, but that's fine.

ZIERLER: What were some of the key discoveries, the contributions of the InSight program?

GOLOMBEK: I would say, we don't fully know. There is so much more that will be learned from the InSight data that hasn't been ferreted out yet. It's a data set that's amazing. The proposal said, "We're going to tell you how big the core is. We're going to tell you whether it's solid or liquid. We're going to tell you the mantle, and the density distribution through it, which will help you determine the mineralogy. Certain kinds of olivine polymorphs or minerals are going to be stable at different pressures and temperatures as you go down, whether the so-called perovskite line is going to be there or not. We're going to tell you the thickness of the crust." It's a 1D from the lander down. Of course, it not only answered all those questions, but because we got large quakes, we've determined the crustal thickness from surface waves elsewhere that have come across this way from one part of the planet to the other. We know a bunch of places where now we know the thickness of the crust. We know the density of the core, and that there's a light element in it. There's substantial evidence to suggest a molten layer at the bottom of the mantle, so not iron-rich but now olivine-rich that's so hot, it's molten, and so exactly what the contributor, the light element contributor of the core is still being debated. It's going to be another 10 years before all of this plays out. That goes directly to how a terrestrial planet coagulates from the planetesimals that exist at the beginning, and whether it starts out molten when the free fall occurs that it gets dense enough that the iron goes into the—it's going to tell you how you build a terrestrial planet. That's even beyond what we proposed. InSight is a huge success [laugh], a huge success. I had nothing to do with the seismometer but I, of course, picked the landing site, and I was the geology lead. What was so fun about it was that the waves not only go through all this other stuff, it has to go through the surface materials. Those geophysicists were super interested in what we could tell about the top kilometer from the geology, and what we could see from the craters and the impacts. It was just so much fun, and a great group of people to interact with. It's just been a great mission.

ZIERLER: Matt, the planning for Perseverance, to go all the way back to the beginning of our conversation, if not the name itself, when did the idea of a sample return mission really start to take hold in the design phase of what Perseverance's capabilities would be?

GOLOMBEK: In the previous decadal surveys, they talked about sample return, and how important that was. There was this recognition, and there had been a number of, as I said, steps earlier to try to get sample return going. But the idea of making a first step using the rover, and finding interesting rocks might help get the rest of sample return going.

ZIERLER: [laugh]

GOLOMBEK: But if you couldn't get the rocks that we have gotten that suggests that this was a completely habitable environment, one that you want to bring those samples back to do the next level of looking at, that having those sitting and ready to go, that that would be part of the impetus to get a sample return to happen. I think there was probably some thought process like that that this is the first step. If the samples just sit there for a while, OK, they sit there for a while. Eventually, we're going to figure out how to go and get those samples, and bring them back, so why not collect them, at least, for the start?

ZIERLER: The idea is that there wouldn't be the next rover to do this? It would be Perseverance?

GOLOMBEK: It would be Perseverance, yeah, it would be Perseverance.

ZIERLER: Matt, how did you operate—?

GOLOMBEK: The idea was, just in general terms, you trade out the sample laboratory on Curiosity. It's the same rover, basically, the same rover. But instead of a sample laboratory that's in front that you feed samples into, you now design a system that allows you to collect and seal samples instead. Now there's no laboratory instruments on Perseverance. They're all in situ instruments that are remote sensing, but you can grind down, and look at the rocks. But you're not taking a sample, and sticking it into an instrument. That's the difference. It had a major impact in terms of the instrument selection, and even what the mission would do.

ZIERLER: How did you operationalize all of your experience in landing site decisions when it came time to think about Perseverance?

GOLOMBEK: The job was pretty similar, but different. We haven't had a conversation yet about how site selection has changed, and how dramatically it's changed. Probably the best way to answer your question is just to take a minute and—

ZIERLER: Please.

GOLOMBEK: —give you a little snapshot. For Pathfinder, the landing ellipse was 300 kilometers by 100 kilometers. That's as accurately as you could target a position on Mars. We didn't know the ephemerides. We hadn't been to Mars in years. We didn't know where Mars was. [laugh] We had no tracking of a spacecraft at Mars, so its position was uncertain. To target atmospheric entry that would take you to the landing site was uncertain. We had no new data from Viking 20 years earlier, and the highest image resolution data, you might see something the size of a football stadium. What the engineers were most worried about were rocks the size of your chair. How do you do that? [laugh] How do you go from remote sensing, crude remote sensing data to what does this surface look like down on the ground?

To MER, we had Mars Global Surveyor, and we had the MOC camera, which took images at three meters per pixel. That was a huge advance. Now you could see things that were the size of a car. Put four of those pixels together, and you could see things as big as a pickup truck, and at least you could get some idea kind of what was down on the ground. [laugh] But in addition, there were thermal instruments that were giving you thermal inertia and thermal physical information. That was a huge thing. Then we go to Phoenix, and Mars Reconnaissance Orbiter got there. This is a true story. Prior to Mars Reconnaissance Orbiter getting into orbit around Mars, we had picked four zones on Mars where we were going to use the cameras on Mars Reconnaissance Orbiter to pick this site. That ellipse was 100 kilometers by 30 or 20 kilometers; much smaller than what we had before. The first things that the camera did when it got into orbit—I remember this so distinctly—it took pictures of the previous landers, and it took a picture of Viking 2, which was a very rocky site (20% rock abundance), which they were pretty fortunate they landed to safely at [laugh], in retrospect. You could see the shadows of all of the rocks that you could see from the lander. For the first time, we had a high enough resolution instrument from orbit that we could see rocks that could damage a spacecraft. That had never been the case before.

Now we get to Mars Science Laboratory or Curiosity, and we're landing in a six-kilometer radius. Maybe it was 10 or 20 kilometers, something like that. We got complete coverage in stereo of the entire ellipse, where we made digital terrain models with one-meter postings. We could see slopes on the scale of the lander and the rover; unbelievable information that you could get. All of those previous cases, you determined the probability of success by taking the landing point distribution file of how many times you land close in versus out on this ellipse, to what the hazardousness of the ellipse is. There's always someplace in the ellipse that's not as good. With an ellipse that's 60 kilometers, there's craters, there's bad things in that ellipse that are going to kill your spacecraft. You can't avoid it. You can't find a place that won't have any hazards. All you can do is make the number of times you would land at those places small enough that you still had a 99% chance of success. That is what ruled from Pathfinder all the way through Mars Science Laboratory or Curiosity. We started out with Mars 2020, as it was called, before it was called Perseverance. They weren't quite sure exactly whether they needed some new landing technique. As we were doing this landing site selection, all of the sites that were the most highly ranked by the science community were not safe. [laugh] They got crater rims, and deltas with slopes that would kill your spacecraft, and rocks all over the place. [laugh] They were not going to be safe if you simply landed there, and you calculated a 99% chance. What they did is they used something called Terrain Relative Navigation. They enabled the spacecraft to divert from where you're going to come down hundreds of meters on either side, perpendicular to the landing azimuth, so you're coming in this way. You could go north or south, perpendicular to that, and you could control coming down to any spot along that line. The only way that works is if you use Terrain Relative Navigation. As you're coming in, you're taking images of the surface, and you're matching them to a map that we made using the high-resolution image data from the orbiters. We made the best map humanly possible of the landing site, and we stuck it in the brain of the rover, and it compared it.

Now, when it found a match, it knew exactly where it was. That's important because—this could get more—I'll skip the next part. It's very important to know where you are, because now you'll know now if you map the safe places in the ellipse, you don't need all of the ellipse to be safe. You just need enough places that are bigger than—I forgot—10, 20 meters that have no rocks, and are flat, and are safe, and you mark those as safe places. What you do is you create a hazard map that tells you numerically how likely you are to be safe if you land at that point. As it comes in, it knows where it can divert to, and it goes to the safest spot it can in that line. You say, "Wow, that's pretty cool." Now we have an ellipse that's six kilometers, way smaller than anything. It's got hazards all over the place. It has rock hazards, it has slope hazards, it has inescapable hazards, places where you could land but you couldn't drive out of because of the sand. There's so much sand that you get bogged down, and you would never get out of it, inescapable hazards. We now had to map the entire ellipse, and we had to find all of the safe places. [laugh] We had to be right from orbit so that when the spacecraft makes its decision and it comes down there, it's just as safe as you said it was going to be, and the spacecraft's $2.5 billion dollars. [laugh] Now my job is way harder than it had been. Now I've got to know where every rock is. I've got to know where every slope is. I've got to know where all the sand is. I've got to know all this stuff I didn't need to know before. [laugh] Why'd we get on this whole thing? This had to do with—remind me where we started on this, that I needed to tell you all of this. [laugh] Sorry.

ZIERLER: The question was, if you were able to operationalize all of your previous experience in site landing decisions for Perseverance—

GOLOMBEK: Now, every site selection, you wound up learning some technique or some capability using the remote sensing data to get more information about the surface that you didn't do before. Even every single one, you had an evolution of the techniques. In fact, we had science teams that worked on it. We put out requests for proposals for help. We needed digital elevation maps. We needed mosaics where those were merged together to make a topographic mosaic. We needed the ability to count rocks. We needed detailed high-resolution thermal inertia. We needed atmospheric characterization so that as the spacecraft knows the atmospheric conditions that it's going to go through. If you're coming in with a dust storm, it's a different atmosphere than if you're coming in during clear conditions. We had all this information, and we had all these orbiters and landers, and our previous experience with driving, for example, MER, all these places that we had been, to use as proxies to help us with this next level of characterization on the surface. I would say all of those were probably necessary and needed to enable you to get to that level of detail in terms of characterization of the surface, to be able to do this whole TRN thing in this landing [laugh] that Perseverance did in this place that you couldn't even consider in the previous site selections. They were far too hazardous. You needed all of those orbital and surface missions in the past to enable you to better predict what was down on the surface from what you had seen in orbit, because when you'd driven all these distances with MER and Curiosity, and you'd seen what it looked like on the ground compared to what it looked like in orbit, that took you so much further than you would otherwise. That's the part of being part of a program. It's just not a one-off, and then you forget it. It's where you build on what you learned previously.

ZIERLER: Has machine learning or autonomy become a factor in site selection for Mars science?

GOLOMBEK: Oh yeah, absolutely. The way we count rocks is machine learning. You don't have enough grad students or even undergrads to count rocks by hand. [laugh] Think of this giant ellipse. You identify them by the shadows. If they're this thing that sticks up, and they cast a shadow, the shadow is in fact bigger than the rock, and easier to identify, because it's super low in albedo. JPL was the perfect place, because there had been work on actual hazard avoidance on landing that used a variety of these techniques that they were testing. Using machine learning, basically what we did is we'd take an image, a high-resolution image at 25 centimeters per pixel. We would segment the shadows from everything else. Now you had the shadow defined. We'd fit an ellipse to the shadow. From that, we could calculate the diameter, which is the small axis of the ellipse. The long axis and the angle of the sun tells you the rock height. Now we can measure all the big rocks. They have to be big enough that the pixels will pick them up so we actually could measure all the rocks that were bigger than about a meter and a half. But because we had done this at places on the ground where we also measured the rock distributions, we came up with a model. It's actually called the Golombek Rock Model. [laugh] We developed it during Pathfinder in 1998, and it's worked since then [laugh]— 25 years, the Golombek Rock Model. It tells you what the size, frequency, distribution, if you can estimate what the total population of rocks. We fit that to those measurements, and got incredibly sophisticated with it. That's all machine learning. Could not have done that any other way, and you probably couldn't have done that any other place where you had that mix of talent all together thinking about landing spacecraft. It could not have happened at a university, because universities tend to segment by departments.

ZIERLER: For you, was working at home an easy enough transition during COVID?

GOLOMBEK: Yeah. I still work at home. I've never gone back. [laugh] We all went remote. I guess it was March of two and a half, three years ago.

ZIERLER: Yeah.

GOLOMBEK: I didn't find any difference whatsoever. All of our meetings are done on WebEx or Zoom. All the meetings are virtual so you know what you're doing. Ninety percent of everything I do comes across the internet. It's either email or you're on some website. We are looking at each other on the computer. [laugh] When they started asking people to come back, they had an option if you wanted to be just totally remote, and I applied for that. Everybody said, "Yeah, we don't need him around. We know what to do." [laugh] I never went back.

ZIERLER: Matt, we'll bring the story—

GOLOMBEK: In fact, they made me give up my office.

ZIERLER: Oh, so you can't go back?

GOLOMBEK: At JPL, the space is incredibly tight. It's not palatial like at Caltech. You get these little cubbyholes. I've been in that office 30 years. The day they granted me the off-site, they said, "OK, when are you out?" [laugh]

ZIERLER: [laugh]

GOLOMBEK: It took me a week to pack up that. I just threw everything out. [laugh] It didn't matter.

ZIERLER: Matt, we'll bring the story right up to the present. Nowadays, how much is Mars Sample Return occupying your time?

GOLOMBEK: I'm about a quarter-time Sample Return and I also work on the helicopter, Ingenuity finding airfields that are safe. I'll give you a little backstory here.

ZIERLER: Sure.

GOLOMBEK: When we started out, what's different about Ingenuity, and about Sample Return is they're both susceptible to hazards that you can't see in high-resolution images from orbit. Things that are 10 centimeters in diameter and more than 4 or 5 centimeters high are hazards for the helicopter. The helicopter is this teeny little thing. It's not bigger than your laptop, with little spindly feet. It can't land on a meter-sized rock. In fact, the constraints are the rock has to be no more than two inches, five centimeters high. You can't see that in a 25-centimeter orbital image. We started out, we said, "OK, to figure out the place that we're going to deploy, we need images from the rover." Perseverance would take some images, and we'd scout it out that way. Then we'd say, "OK, this is safe to go." The first five flights, which were the demo part of the flight, they all landed at the same place. Then we said, OK, we might as well use it for something else, so let's go fly somewhere.

The first place we said, "We'll fly and we'll take an image with the helicopter of the surface at a new location, and then we'll fly back to the place we were, and we'll land back there, because we know that's safe." Think about that. It's pretty inefficient for trying to go someplace. You would always have to go there and come back the first time, and then go there the third time. That's not efficient. We had to figure out a way to find a safe place in the high-resolution orbital images that was safe enough for the helicopter [laugh] . That was a bit of a challenge, if you can imagine. But the advantage we had was that we had the rover on the ground, and we had some experience of what it saw. Again, we're relating orbital to the surface. It saw lots of things, and we could characterize that. Then we knew what it looked like from orbit. As it went, we built up an inventory, OK, this is bad, this is good, kind of thing. There are a bunch of other things that are beyond that, but that's what you use. You're using that inference, and the experience base of what you did on the surface to now predict. It's not just, what, eight or nine landings. Those were the lander spacecraft from outer space. But we've picked—what are we up to?—40-something sites for the helicopter, based on orbital high-resolution images, using similar kinds [laugh] of things. The lander, the Sample Return lander is susceptible to things that are 30 to 40 centimeters. That's only bigger than one pixel in orbital images, so small rocks are difficult to see. We're trying to infer even smaller things from orbit. That's the challenge. [laugh]

ZIERLER: Are you satisfied at this point in your career that you've achieved the right level of balance between science and administrative responsibilities?

GOLOMBEK: Yeah. I don't do much admin. I run science. I mean, running a landing site selection, there's some admin, but it's the science of what it's doing that's most important. I don't follow the contracts. I get other folks to do that. But what is that contributing to what we're learning about the landing site? That's the part; that's like doing science. Then I do a whole bunch of it myself as well, just because I'm curious and interested. [laugh]

ZIERLER: The right balance for you is very little administrative responsibilities? [laugh]

GOLOMBEK: Yeah, that's right. [laugh] That's right.

ZIERLER: Matt, now that we've worked up to the present day, for the last part of our talk, if I may, a few retrospective questions about your career, and then we'll end looking to the future. Having spent so much time on Mars, being a full-time Martian, what does that tell us about this period in JPL's history? Would that have been possible in an earlier generation? Do you think it's possible in a future generation? Is there something really idiosyncratic about the timing of your career?

GOLOMBEK: I think I've lived through different chunks. I call the doldrums early on, where you didn't have a lot of new data, and everybody was trying to ring out whatever they could from the old data. But the last 20 years have been the renaissance of Mars science and of Mars exploration. There's been no other time where we have gone from this tech demo with this little baby rover to a thing that's as big as your car, and look at what it's doing.

The number of missions and the level and different kinds of information that they brought together, and the synergy between those informations, both orbit and surface, has been just spectacular. I have no complaints whatsoever. [laugh] Now, the difficulty in the future is that most of the money is going to Sample Return, and Sample Return is an engineering job. It's already been said by NASA, there won't be any science. It's just go get those samples, and bring them back. The science is after you bring the samples back. I think there's a concern, not just mine but among the science community, that the Mars science community is going to have less support. There's going to be less missions, there's going to be less opportunities to work on it, and it's probably going to shrink somewhat until we get the samples back. Then it's different. It's mostly petrologists and geochemists that work on samples. That's very different from most of the people working on this now.

ZIERLER: If you'll permit yourself or if you ever permit yourself to detach from being a hard-nosed evidence-based scientist, have you gone through periods where you're more or less optimistic about the likelihood of life on Mars?

GOLOMBEK: It's the journey. Either way, we're going to learn amazing things, and amazing things about our neighboring planet, and either answer is just as profound if you ever get to it. I don't want to say I don't care, but it doesn't matter which answer. The journey, and how you get to that location, and what's the evidence, and what else you learn in that while you're doing it, that's the truly interesting aspect to me.

ZIERLER: You've set yourself up for a win-win perspective? There's no losing equation here?

GOLOMBEK: No losing here.

ZIERLER: Matt, in the grand sweep of history, whatever that answer ultimately may be, what do you see as your contributions to answering it?

GOLOMBEK: It takes a lot of people to make a successful Mars mission. I'll give a little pump to JPL. There's no place else in the world where at one location you have everyone you need to conceive of design, build, launch, operate, get the data back, and write papers about it, all in one place. There's nowhere else that includes all the expertise in one place. There are places that do parts of all of that, but nowhere else in the world where all of that happens in one place. [laugh] I hate to talk about economics, but everyone's on soft money. You need a charge number to charge for your salary, so you have interest and impetus to work with varieties of people on a variety of different things. That synergy of you cannot land a spacecraft without scientists and engineers working hand-in-hand. If there's a hallmark of my personal career, it's I am right at the middle of that. Landing a spacecraft is the rubber on the road. [laugh] It's where the airbags hit the surface. If you want to land that spacecraft, you have to work half-time with the engineers, and you better be a good scientist because it's not a hypothesis whether there's a rock there or not that's going to wreck your spacecraft. You better be pretty sure to the tune of billions of dollars. [laugh] I don't gamble. I don't go to Las Vegas. I don't gamble on landing sites. It's show me the data. [laugh] You better know, to the best of your ability, you better do everything humanly possible to make sure that that spacecraft will land safely. That's probably my contribution right there.

ZIERLER: Finally, Matt, looking to the future, what's your timeline, and are you attaching that to however Mars Sample Return might play out? To the best of your ability, do you want to be around to see what happens?

GOLOMBEK: I don't want to tell you how old I am, but I am almost certainly not going to be around. [laugh] I certainly won't be a full-time employee. I don't think they have them that old. [laugh]

ZIERLER: [laugh]

GOLOMBEK: No. I'm probably towards the end of my career here, and I don't need anything else. I've done it all. [laugh]

ZIERLER: You're good?

GOLOMBEK: I'm happy!

ZIERLER: Matt, this has been a wonderful, wide-ranging, really fun conversation. I'm so glad we were able to do this. Thank you so much.

GOLOMBEK: You're quite welcome.

[END]

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