Bullaki Science Podcast

17. Mars Perseverance Mission | Prof. Nicholas Tosca

March 04, 2022 Bullaki Season 1 Episode 17
17. Mars Perseverance Mission | Prof. Nicholas Tosca
Bullaki Science Podcast
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Bullaki Science Podcast
17. Mars Perseverance Mission | Prof. Nicholas Tosca
Mar 04, 2022 Season 1 Episode 17

Nicholas Tosca is a Professor the Mineralogy & Petrology in the Department of Earth Sciences at the University of Cambridge. His research interest include understanding the co-evolution of life and environments through Earth’s early history. He’s also science team member of the Mars 2020 Perseverance Rover Mission, currently exploring the ancient surface of Mars and seeking signs of ancient life.

In this Bullaki Science Podcast Prof. Tosca talks about the PIXL instrument on the Perseverance Rover and how knowledge on Mars geology can advance our understanding on the origin of life on Earth and elsewhere. 

The video is available here: https://vimeo.com/manage/videos/680589336

Recorded: 17/02/2022
Published: 22/02/2022 


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Show Notes Transcript

Nicholas Tosca is a Professor the Mineralogy & Petrology in the Department of Earth Sciences at the University of Cambridge. His research interest include understanding the co-evolution of life and environments through Earth’s early history. He’s also science team member of the Mars 2020 Perseverance Rover Mission, currently exploring the ancient surface of Mars and seeking signs of ancient life.

In this Bullaki Science Podcast Prof. Tosca talks about the PIXL instrument on the Perseverance Rover and how knowledge on Mars geology can advance our understanding on the origin of life on Earth and elsewhere. 

The video is available here: https://vimeo.com/manage/videos/680589336

Recorded: 17/02/2022
Published: 22/02/2022 


- Subscribe to our YouTube channel: https://www.youtube.com/bullaki 
- Support on Patreon: https://www.patreon.com/bullaki   
- Spotify: https://open.spotify.com/show/1U2Tnvo1PZY4Fu4QLHURJV  
- Apple Podcast: https://podcasts.apple.com/gb/podcast/bullaki-science-podcast/id1538487175 
- LinkedIn: https://www.linkedin.com/in/samuele-lilliu/  
- Website: www.bullaki.com  
- Minds: https://www.minds.com/bullaki/ 
- Vimeo: https://vimeo.com/bullaki  
- Odysee: https://odysee.com/@bullaki:0

Samuele Lilliu (SL) (00:00). Professor Nicholas Tosca, thank you very much for joining me today. Thank you very much for being in this podcast. So your expertise is in Mars geology, and also seeing how Mars geology relates to our planet. I was wondering, when did you start being interested in this planet? You've been working on this subject, topic, for like 20 years of your life. I've seen that your first papers were in 2004-2005.

Nicholas Tosca (NT) (00:31). Yeah, that's right. I guess it was since I was a grad student. My training is in geochemistry, formerly what my PhD was in, which is all about the chemistry, natural waters, how minerals form and how those minerals relate to chemistry and climate. But the project that I enlisted for, as a PhD student, was investigating the early climate of Mars. At that time, 20 years ago, we had a lot less data than we do now. And right towards the beginning of my PhD, my PhD advisor, Scott McLennan, joined the Mars Exploration Rover team, and got myself and a couple of other of his grad students added to the team. So my PhD was brought into sharp focus by engaging with the team at that time and that was just a wonderful experience.

SL (01:29). What rover was it?

NT (01:30). This is the Mars Exploration Rover. There were actually two of them, identical copies, sent to different locations in the planet. One of them landed in a spot and analyzed ancient sedimentary rocks, which is a big discovery. The other one landed in a spot, a crater called Gusev Crater, which was mainly filled with igneous rock. So it was a different sort of story and some important discoveries from that mission to...

SL (01:55). Igneous rock, is what? Magmatic rock from volcanos?

NT (01:59). Yeah. When magma and lava crystallizes, there's a lot of that type of rock exposed on the surface of Mars. That's the source of the sediments, so wind and water break that material down and form the sediments, which end up getting deposited mainly in craters. They're the biggest holes in the ground.

SL (02:21). Was there any exploration of lava tubes? Do you know lava tubes on Mars? I think those are holes left over by the magma circulating underground. There are plenty of lava tubes on Mars, I think you can see images from the satellite. Has there been any exploration of those tubes?

NT (02:43). I know that those features have been interpreted based on orbiting imagery. So basically, high resolution satellites that take those images and allow geologists to infer that they might be lava tubes. But to my knowledge nothing of that type has been encountered by landed missions and missions that have actually operated on the surface.

SL (03:07). There have been so many proposals for Mars colonization and I think lava tubes were good candidates, because there you can shield from ionizing radiation. 

NT. Oh, I got it. 

SL. Is it possible that might be life in these things, within the caves?

NT (03:29). I don't know. The way we think about life is that we normally think about microbial life as being the likeliest possibility if Mars ever hosted life and I can sort of go into the reasons why that is. It's basically because microbial organisms dominated this planet for most of its earliest history. 

There's a huge divide between microbial life, specifically bacteria and archaea, which are simple single cells with a membrane around them and some DNA and a few other components, and much more complex life, like plants, animals, humans, which are built on a very different type of cell that has some incredibly complex components in it that allows that cell to harness huge amounts of energy and to do really complex things. That's really the platform for most of the complex life that we know and love when we look around us today. 

SL (04:31). From an earth scientist [perspective], where do you think we are now in terms of understanding how life came about in our planet? The so-called abiogenesis?

NT (04:42). Yeah, that's a great question. It's an interesting time to be asking these questions because, in order to tackle that question, you need to know something about chemistry, so the chemistry and the pathways required to make the building blocks that life needs. You need to know something about the environments, the natural environments that might have provided those chemicals and allowed those pathways to operate. Then you need to know something about how environments might have operated through time and potentially on other planets to really assess the likelihood of those pathways operating elsewhere. So all of those aspects have undergone pretty significant revolutions in the last few years and this is part of what makes it so fun to be an earth scientist interested in these questions now. 

There are groups at Cambridge, for example, John Sutherland’s group at the Laboratory for Molecular Biology in Trumpington and they specialize in organic chemistry, basically producing the key building blocks that life needs. What's interesting is that they've done this very successfully and they've shown that multiple types of building block can be formed in the same system. They're very specific about the molecules that are needed and the chemical and physical conditions that are needed. 

That's great, because as a geochemist, you could say, “Okay, I can think of environments that could potentially do that”, or it raises questions “Well, if that component in a, say, for example, hydrogen cyanide is necessary high concentrations? How is that going to get there? How did it get there in the early Earth? And what was it about the earlier if that might have allowed that to happen?” 

So I think we're in an interesting place now where we're asking very detailed questions that are leading us through a logic that that hopefully, will lead to even more discoveries in the future.

SL (06:40). So looking at the John Sutherland’s papers, I can think about this huge graph where they start from very simple molecules, and then they do some reactions, and they get more complex molecule. And then they start again, from these more complex molecule to get an even more complex molecules. So what you guys are doing is trying to understand the conditions on this planet that made this possible. Well, my question is, in terms of boundary conditions and initial conditions and so on, there might be so many conditions under which this chemistry happened. So how do you identify what might have actually happened? Is that based on what knowledge we have on geology? And okay, let's try to match things. How does it work?

NT (07:32). Yeah, that's a great question. It's very likely that multiple pathways could provide you with the building blocks you need and perhaps even multiple pathways might lead you to complex systems that start to look and adopt the traits that life needs. I guess, distinguishing between those, as a scientist, you would want to do that based on observation, so which pathways fit actual observations, data that we have, about the early Earth. This is a big problem, because we don't have much data about early Earth environments. Earth has plate tectonics, the rocks that were formed during that period are mostly long gone, they've been consumed and destroyed by plate tectonics, and those that do exist, it's very difficult to extract meaningful information about environments, it's possible…

SL (08:26). How do you find them out? The oldest, the oldest rocks on this planet, how do you find them out?

NT (08:30). Yeah. Well, normally through isotopic dating, so you can use multiple isotope systems that have known decay times or half-lives…

SL. So a sort of clock. 

NT. Yes, exactly… Exactly… And measure the ratios of specific isotopes that are present now and know something about the starting point of those ratios and you can work out how old the rocks are. But in terms of where to go that's what geologists do best, they understand the most ancient terrains and they know where to look and where the best candidates would be for old sedimentary rocks.

SL (09:08). So for organic matter you use carbon decay I guess, but for minerals what do you use? Uranium, radioactive materials?

NT (09:18). Uranium-lead system works well, because they've got long half-lives and so they give you good resolution at the hundreds of billions of year timescale.

SL (09:33). Okay. Hundreds of millions of years. So where are the oldest places on this planet?

NT (09:42). Well, there's a difference between the oldest rocks and the oldest minerals that were once part of the rock that has basically been obliterated. The oldest rocks are highly metamorphous rocks. For example, Greenland is a host of some of the oldest known rocks on Earth, because that's a segment of the continental crust that has pieces of it that survived multiple tectonic episodes. 

Then there are old minerals that were once part of sedimentary rocks, and you've only really got the minerals left. There's a mineral called zircon, which is a zirconium silicate mineral, which is really intensely studied by scientists interested in early Earth environments because it can record certain aspects of the hydrologic cycle through oxygen isotopes. The problem is that those zircons don't exist in sedimentary rocks anymore. They exist in pretty metamorphosed rocks. So you've got to strip away all those layers of complexity to sort of get back to earlier Earth environments.

SL (10:53). So basically, from the analysis of rocks can we get an idea about the climate, what climate was present back then…

NT (11:02). Yeah, so there are two ways you can do it. You can look at the zircons and isotope studies of zircons can tell you something about the hydrological cycle, perhaps even temperatures at the time, although there are pretty significant errors associated with that. Another way you could do it is through modeling. So you know rough boundary conditions and you can run computational experiments to understand how the earliest climates might have behaved. The problem there is that there's very limited data with which to check those models against. 

There is yet another way, which is to go to Mars and that's sort of where my interests have come in. Because one of the great discoveries of Mars exploration over the last 20 years is that Mars hosts a pretty extensive sedimentary record. So there are sedimentary rocks that were deposited in environments that hosted liquid water that record in time and space what the climate was doing at the time, and they're beautifully preserved, so none of these high temperature, metamorphism. Mars didn't have plate tectonics. So these rocks, if you can get to them, can be studied, and they record exquisitely detailed information about what the climate was doing, how it changed over time and whether or not those environments could have potentially hosted life, microbial life.

SL (12:28). Is it safe to say that the conditions on Mars and our planet were similar 4 billion years ago? Did Mars have the sort of convection currents of molten nickel and ion in the outer core? Did it have that? Do we know that? So did it have a magnetosphere and all these things? And then also, when did that stop? When did this dynamo effect stop and why it stopped? Do we know that?

NT (13:02). Good questions. So I guess if started off in the first question, Yeah, Mars and Earth were similar but different, and we can go into the details and what that means. 

But yeah, starting with the core, Mars is a smaller planet. There is evidence that it has an iron-nickel core, so much like the Earth. We know that because we have good estimates of the composition of the rest of the planet, the silicate portion of the planet, the crust in the mantle from meteorites that have landed on the Earth, and now from orbiting satellites. Then we have some information about magnetism, about what the magnetic field was doing very early in its history. 

SL. How do you know that?

NT. So there are magnetic measurements that can be taken from meteorites and from orbiting measurements. The orbiters can actually feel gravity anomalies and record magnetic anomalies. If you look at the ages of those rocks and their magnetic signals, you come to the conclusion that really early on Mars had an active magnetic field and then something happened to it and it stops. One hypothesis is that the inner portion of the core basically stopped convecting or, I guess, it would really be Mars's outer core, because our inner core is solid, it's largely in iron-nickel alloy, the outer core of Earth is liquid, and that convection is in large part why we have a magnetic field…

SL (14:44). Because of the electric currents moving around…

NT (14:46). Exactly. And that's really useful for us because it protects the Earth against solar radiation, it keeps our atmosphere in place. The issue with Mars is that even though it started off the same way, once the outer core stopped convecting, the magnetic field or the dynamo is believed to have stopped and then that's when it's set off in this pathway towards this sort of cold, dry desert.

SL (15:10). Yeah. Because I mean, if you don't have the sort of Van Allen belt, basically your atmosphere gets stripped away, right? Some of the gases that are in the atmosphere get decomposed. 

NT. Yeah, that's right. 

SL. Oxygen, how long does it last, if there was oxygen [back then]?

NT (15:33). Well, so how long oxygen can last in the atmosphere is a sort of a push and pull between the rate with which it's created and the rate at which it's destroyed. There are a lot of processes that could destroy oxygen, so basically reducing compounds like ferrous iron or anything else that that can react with it quite readily. We don't really have a good estimate. I mean, the current thinking is that Mars has a little bit of oxygen now…

SL (16:04). 0.15% or something like that…


NT (16:07). Yeah, that's right, and it's thought to have been created mostly in the upper regions in the atmosphere through photochemical reactions.

Earlier in its history it's thought that, because volcanism was so vigorous and that volcanism on Mars is likely to have released reducing gases, that those reducing gases are likely to have kept oxygen in check. What's really fascinating is that for a long time, the standard view was that early Mars was reducing, didn't really have a lot of oxygen and then it sort of very slowly kind of increased to a slightly higher level. If you piece together all the information from the rocks and you put together climate models of how Mars climate might have behaved, the story actually turns out to be much more complex. So now the thinking is, and this was summarized in a recent paper just last year by Robin Wordsworth, who is a climate modeler at Harvard, the thinking is that the redox state of the Martian atmosphere could have been very dynamic, could have changed from oxidizing to reducing. And that's a concept that Earth scientists who studied the early Earth have not really thought about before, because Earth behaves very differently.

SL (17:24). So that's one of the differences between Mars and our planet. But what the thing that makes Mars a good proxy for our planet?

NT (17:37). So that would be ancient Mars, most of all, so. That's the time when Mars hosted liquid water. And based on piecing together analyses of the sedimentary rocks, we concluded that when liquid water was around, some of those environments were similar to environments that exist on the Earth today. So early Mars and the sedimentary rocks that were formed in that time provide a record of a planet that looked similar to the modern Earth. 

But in detail, I think there were important differences. Earth is a watery planet, we've got oceans, and we’ve had oceans pretty much from the start. Mars had water, but it looks like that water was a transient phenomenon. So it was around, it moved around in the planet, it made minerals, it participated in events that extended across millions of years. But there are also intervals that look like they're characterized by very dry environments. So the thinking about early Mars is that it was wet, but not as wet as the Earth. [Questions like] “How long water was there? When it disappeared, and how long it stayed dry for?” are really critical to answering the question of “Could it have hosted life? Was water around long enough, and in enough quantities to really make important chemistry happen?”

SL (19:01). So that topology of Mars, when we look at Mars now, we can see maybe three regions. There is a region in the north, which is flat. Would it make sense that there was an ocean and then the south was a huge continent? Because our planet it was something like that, right? We had a huge continent and then the rest was ocean.

NT (19:22). Yeah, that's right. So the continental crust on Earth formed through processes that involved basically partial melting of the upper regions of the mantle and that's a process that is enabled by plate tectonics. The difference you're referring to on Mars… the south part, is topographically really high and then the northern part is very low, it's basically a large basin or series of large basins, probably didn't form in quite the same way. But nevertheless, I think a lot of people think that the north might have hosted an ocean at one time or maybe very large lakes.

SL (20:05). About the sort of water we have on Mars, you wrote a paper in 2005[SciVPro1] , where you discussed the kind of water that’s in Mars. And you discuss the issue of, okay, it is not only about water, but it's also about salinity and if the salinity is too high, in our planet, organisms tend to die, they cannot survive that. Right? So, what was the situation there on Mars? What kind of water did we have on Mars?

NT (20:35). Yeah, that was an interesting paper and we received some press about it. And also it generated a lot of sort of heated debate within the scientific community. So this was during our involvement in the Mars Exploration Rover mission. One of the rovers, Opportunity, was analyzing sedimentary rocks that were loaded with salt minerals. By analyzing the minerals present in those rocks and the sediments in the sedimentary structures, the team was coming to the conclusion that the waters that form those sediments were acidic and, most of the time, pretty salty. 

A large part of my PhD research was focused on the exact chemistry of that, and replacing constraints on how acidic and how salty. I started working with Andy Knoll at Harvard, who pitched the idea that, well, “Could this have been a problem for life?” Because life on Earth, as we know it, microbial life, has very strict tolerances to salinity. If salinity gets too high, so things get too salty, or, to put it another way, if H2O isn't present in enough quantities to enable molecular biochemistry to happen, then microbial activity will shut down. 

This is the reason why you can keep a honey in your cupboard for years and still eat it, because there's barely any water. We can quantify that by something called water activity, which is a thermodynamic measure of how much molecular water is there and able to facilitate chemistry. It's also the reason why the British were able to conquer much of the rest of the world, because their navy discovered that if you just salt your beef, you can keep it around for a lot longer. 

So I mean, using that as a parallel, we dug into the details of “What are the limits of salinity for microbial life on Earth? How does it work?” And then if we use that and turn to Mars and look at the minerals there, and look at how salty the waters are, “Is that good or bad?” 

It turned out the answer was actually pretty bad. But, you know, we don't necessarily think the whole planet was like that all of the time. So what we did is we wrote the paper saying, based on this location, which is potentially the youngest location on Mars where there were significant quantities of water, this is bad for life. There are reasons why what we know about prebiotic chemistry won't work. There are reasons why what we know about microbial life just wouldn't be able to survive. 

It was a conclusion that a lot of the scientific community weren't happy with, because sometimes when people think about microbial life on Mars, they do so with a with a hope, or a preconceived notion that there are environments that that must have hosted it, because that's the exciting conclusion. We thought it was useful to point to environments that were bad and compare those two environments that might have been better.

SL (23:37). Yeah, but maybe there are other regions where the water activity is higher. So in our planet it’s between 0.8 and 1, something like that. 

NT. Yeah, that's right. 

SL. 0.95 or something. In the [Mars] region where you went it was like, 0.45-0.5.

NT (23:53). Yeah, it's very low. We just wanted to shift the conversation and say that water is important, because missions on Mars had been focused on discovering evidence for past water, but the chemistry of that water matters if we're going to talk about the capacity of environments to host life.

SL (24:12). So we sent so many missions, rovers, starting from the Viking [probes] in the 70s. But more recently, I mean, we sent… I think the Viking [probes] were just stationary, just probes, and say they stayed there and that's it. Then we started sending rovers beginning of 2000s, in the 90s, right?

NT (24:34). Yeah. 1997 was Pathfinders about the size of a microwave.

SL (24:38). Yeah. And now we just landed the Perseverance Rover and you're part of the mission, right? What's your role?

NT (24:50). Yeah, so I'm a what's called a participating scientist in the mission. So most of the science team is put together in the few years before the mission launched. Then toward the end, NASA released a call for a dozen more scientists who could conduct an investigation using rover data to further the goals of the mission. The goals of the mission are to identify an area on Mars that was potentially suitable to have hosted life and suitable to preserved evidence for past life. And also to select samples that offer the best chances of recording evidence of past life for future return to Earth. 

So I propose an investigation saying, well, you know, my expertise is in geochemistry and so what I can do is we can look at the minerals and try to unravel the chemical details of the waters that were there. That's important because it links to climate and it links to the capacity of Mars to host life. In addition to that, I'm also a member of the PIXL team. There's an instrument on the rover, which is called PIXL, it's actually called Planetary Instrument for X-ray Lithochemistry. It's positioned on the end of the arm. It's a Micro Focus X-ray fluorescence spectrometer. So simply put, it produces chemical maps of the surfaces of rocks. That's critical, because although you can take a rock and say, bash it up and analyze the chemistry of it as a whole, what you're losing is the information that individual minerals and their relationship to each other tell you about the sequence of events that have impacted that rock. That's what PIXL allows us to do. By producing these chemical maps, we can see the minerals, we can work out the timing in which they formed, and we can actually start to be specific about events that affected the history of these very ancient rocks.

SL (26:56). Nice. So there's the rover. And I think your PIXL [instrument] is one of the 23 imaging cameras…

NT (27:12). PIXL does have a camera associated with it, it's called the micro context camera. That camera collects images taken in the visible along a couple of different colors. Then also it collects near infrared image and UV image as well. So it provides some spectral information to help identify minerals. But those images are taken separately from the process of hitting the target with X-rays and actually collecting the map…

SL (27:43). So that’s a multispectral camera. 

NT (27:49). Yeah. And that camera was developed by a team in Denmark, that that the PIXL team worked closely with.

SL (27:55). I think I've seen papers on the engineering of the instrument. So with the PIXL do you do in-situ scans in the sense that the arm goes to the rock without removing it? Or first you cut the rock and then you bring it inside? What do you do?

NT (28:11). Yeah, so ideally, we want to look at what's called the fresh surface of a rock. These are have been set in the surface for millions, if not billions of years, they are billions of years old, but a lot of them have been excavated and unearth, and so they've been subjected to the elements. 

SL. Wind…

NT. Yeah, exactly. What we want to do is grind into the rock to… if it's a sedimentary rock or another rock that can tell us about environments or water, you don't get a fresh picture of where the minerals are. So what the rover does is it uses a tool, which abrades a patch into the rock, a circular patch, and then it actually has a dust removal device, powered by gas that basically just blows the dust out of the way. So you end up with this nice fresh surface that you can then study with, with PIXL. And there are other instruments on the arm as well. SHERLOC [Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals] is a complementary instrument. That is a Raman spectrometer, a form of vibrational spectroscopy, where you hit the target with a laser. The minerals, the mineral lattices respond to that and produce absorptions that can tell you about mineral structures. That's very handy because PIXL gives you the chemistry, SHERLOC gives you information about mineral structures. So if you do the two together, you can get a very, very detailed look at what's in the rock.

SL (29:37). So you can do image registration basically, you can overlay the images and get different information from different types of instruments on the same scan area. 

NT. Exactly. 

SL. That's amazing, sort of multi-domain imaging. 

NT. Yeah, yeah. 

SL. One question I have is that the upload speed of the communication system, the RADAR, sorry, you don't really have a RADAR, the satellite. So the upload speed is maximum 2Mbps at intervals. And then you have other satellites that transmit at lower bandwidth. So my question is, do you do any in-situ analysis and then you send over the synthetize data or you send all the raw data, which is huge I guess? What you do?

NT (30:30). Yeah, so the data are prioritized in terms of the most important data that we need to get back soon. Those are referred to as decisional data. Those are really data that are contained in images. So if the rover moves somewhere, the first thing it will do after it moves is take images and a panorama of where it is. That is used to plan the next drive to assess hazards. It's got autonomous hazard avoidance software on it. But obviously, that's important information, because the team needs to use that to make decisions about what happens next and whether or not it's safe to proceed. So the data are all prioritized and there have been in ordered priority. So those images usually come down first. 

If they're very important science experiments that were conducted that the team will need to work with and use for subsequent decisions, those are bumped up in priority as well. So sometimes that the PIXL data are quite high up in priority. 

But usually, there are smaller data products that are engineering related that just tell us that experiments executed properly and record of the thermal characteristics of instruments and components on the rover. And that that all comes down in relatively short time.

SL (31:58). Okay, so the reason why I was asking that is because in new military [strategy] philosophy, there is this concept that they're trying to put more and more processing power to the devices, to the sensors, where they are, rather than sending all the stream of information to the command and control, because that saves time, makes the communication faster. But that requires processing power, where you're using the things. I think now with the modernization of computers and chips, and all these things, this is becoming more possible. So I was wondering whether… there must be a very powerful computer on board, right?

NT (32:46). There is. Yeah, absolutely. I don't know a lot the details about the computers that operate different components, because there are several sort of CPUs on the instrument.

SL (33:08). Okay. So it's not the only one, there are multiple… Okay.

NT. I believe so, yeah.  

SL. Then the other thing is that, of course, you cannot do… I don’t know what people think, but maybe they think you can control the [the rover] in real time. But that's not the case, there is a delay of between 5 and 20 minutes, depending on the relative position between Mars and our planet. So it takes time to get stuff, you couldn't have a conversation with someone staying on Mars in real time. If you were chatting with that person, you would need to wait for maybe 4-20 minutes to get… “Hello, how are you?”… then you wait 20 minutes… “Fine”. Okay. So if that's the case, when you run things on the rover, how do you do that? Do you send a stream of commands, and then the robot executes them. How does it work?

NT (34:01). Yeah, there's a whole process. I mean, as you can imagine, the mission costs upwards of a billion dollars. So you wouldn’t really want to receive the data and a few minutes later, say, well, “Let's just go over here”, you know, “Let's fool around a little”. There's a whole process. The instructions are sent to the rover, the rover will execute certain steps and then send those high priority data back as I mentioned before. The team has developed a way of working that wastes almost no time in the sort of cycle of events on Mars. So after the rover conducts the experiments that’s what it needs to do. At night, it can only do certain activities. It can't really image at night. There's no point in doing that. You could do some imaging…

SL. You could do fluorescence, right? 

NT. Yes, exactly. But for the most part, the nighttime is used to do other activities, engineering related activities, thermal checks and heating, and that sort of thing. So during that time, that's when the team have the data and they're working with the data and deciding what the next steps will be. We actually have a process where we plan the tactical timeline, which is the following day, and we have a process where we plan the more strategic timeline, which is, say the next three to five days. Those processes are operating in parallel with slightly different teams. What it means is that we're in a constant cycle where we're planning the next day and we're looking ahead and planning the next three to five days. And we continue to send the days to do list and time, for the morning, when the rover is in a good position to do those activities. So basically, the science team and the engineers are working almost around the clock to make sure that the planning process, and the operations process is as efficient as possible.

SL (36:12). The PIXL, I was reading the paper from the Danish Group and I think they were mentioning that… so, with this PIXL instrument, you can just go to a point and get a single spectrum, but you can also do a raster scan. So each pixel corresponds to a spectrum. I understood that this is something that takes a very long time and they were planning to do it overnight.

NT (36:38). Yes, that's right. So that's usually how we collect most of the map scans. So as you can imagine, it takes time to collect many many points that are finely spaced. Some of the maps we collect are, say, five millimeters by seven millimeters and we'll collect 1000s of spectra across that area. Usually that's done overnight, it takes hours to do. But you can also do shorter scans, line scans, just take a few points along the line, or a few rows at points to sort of get some spatial information. Those line scans are used as sort of a preliminary scan to help the team decide what's there and then where we would like to place our detailed map that's going to take a few hours to do.

SL (37:24). So a rough scan. What were the major findings from the PIXL instruments? Is there anything you can talk about that is not confidential?

NT (37:33). Yeah, I think there's plenty to talk about that's already been released on the JPL website. So for example, PIXL has discovered a really complex and interesting history that involves water. I should say that the area that we've been operating in for most of the first year is really in the floor of Jesero crater. One of the reasons why the rover went there is because there's a sedimentary deposit, it's a delta deposit. There's an inlet channel and outlet channel in the Jesero crater and there's a delta on one side of it. So, before we go to the delta, we're going to be spending a lot of time on the crater floor, although we've just about wrapped up that campaign. 

SL. That's the starting point, right?

NT. Exactly, that’s it. That’s the crater rim outlined in brown. That’s the landing site. We've been operating in the region of that dot a few kilometers around that. You can see the delta deposit just to the sort of the northwest of where that that landing site is.

SL (38:55). So this is basically where there was a lake, right? And those are the connecting channels, the sort of river.

NT (39:04). That's right, the inlet channel is just at the top of the screen. And that's just the sort of the entry point of where water flowed in. And because that water hit a standing body of water, there's a velocity change that causes the fine grained sediments the waters carrying to be deposited. That's basically what results in delta deposits. So there's the whole delta deposit sort of fanning outwards, down. And the white line was sort of a one possible long term traverse that the rover was planning on taking over the long term course of the mission. Over the next few years we'll be wrapping up our campaign in the crater floor, spending time on the delta deposits and we'll even move past that, investigate areas that we think were the margins of the lakes, so in sort of the shorelines of the lake, there's a lot of interesting minerals and deposits there, and then even proceed on to the rim of the crater, which probably records hydrothermal environments.

SL. Where is that?

NT. That's out there, just along the upper left hand side, you can see the hills that represent the crater rim. 

SL. So on top…

NT. Yeah, yeah, sort of where that dashed line is. That's where the rover can traverse upwards and start to explore the rim of the crater. I mean, what's really fascinating about this site, and one of the reasons why it was picked is that the site hosts a diverse set of ancient environments. There's the crater floor, the delta, the rim of the crater, all of these things can give you lots of insight into environments that may have been suitable for microbial life.

SL (40:57). Okay, and so those sedimentary rocks, we haven't encountered them yet, right?

NT (41:04). No, that's right. So because we've been spending most of our time in the crater floor, one of the surprises to us [is that] we were all expecting to find sentiments even on the crater floor. One of the surprises is that there are a lot of igneous rocks exposed in the crater floor. So again, these are rocks that crystallize from high temperature magmas and lavas. What's interesting, though, is that those rocks were still interacted with water. 

SL (41:33). They were submerged by water…

NT (41:36). Yeah, yeah… or water percolated either from the surface downwards, or from the ground up to deposit minerals in those igneous rocks. Those rocks are already recording a pretty complex history of water. We haven't even gotten to the delta yet. So one of the questions is, well, you know, “How does that relate to when the lake was filled and when the delta was deposited, was that part of the same event?”, “Are we talking about events that happen much later or even before the delta was deposited?” So there are a lot of interesting questions that we can test as we proceed towards the delta.

SL (42:15). Has there been any thinking in terms of what… we know those prebiotic chemistry reactions… is that environment suitable for those ones?

NT (42:25). It could be. One of the interesting things, if we go back to what we were talking about at the beginning, some of the work that's come out of John Sutherland’s lab, one of the conclusions from their work is that compounds like hydrogen cyanide and phosphate are needed in pretty significant abundances. It turns out that lakes, and we think ancient lakes on the early Earth could have provided those components in suitable concentrations, so a lake is a good environment. We also know from the Earth that lakes host a diverse array of microorganisms and the evidence from those microorganisms is contained in the sediments that are deposited in the lake, either on lake floors or in carbonate minerals deposited around the lake margins. So it's a good environment to go to, it's an environment that we'd refer to as habitable. What we know about microbes on Earth, those microbes could have lived in Lake environments and we know that those like environments are good at recording evidence, because there's a difference between habitable and environments that are likely to preserve evidence of ancient life. So really, you want both and I think that's the reason why the rover ended up going to Jesero Crater.

SL (43:48). The rover is also equipped with tools that can identify fossilized bacteria, right? So in our planet, we found bacteria fossils, right? How do you do that? Just by optical microscopy or is there any other chemical analysis you can do?

NT (44:09). Yeah, that's a good question. I mean, one way to think about this is if we sent a rover somewhere on Earth, to some of Earth's most ancient sedimentary rocks, would it find evidence of life? Would it be able to detect it? How is that we can find evidence of that? So we can find what are called body fossils, so fossilized microbial cells in sedimentary rocks on Earth. So sediments that are good at preserving those are sediments made of silica. So silica is a chemical component that was actually present in abundance in the Earth's early oceans, that silica has this special property that it loves to attach to organic matter, and especially a decaying microbial cells as far as we can tell, it's actually the process that controls the formation of petrified wood. So, you know, you find petrified wood. It's basically wood that's completely templated in crystalline silica and silica preserves, you know, a detail down to

SL (45:14). Are you referring to those forests? Petrified forests?

NT (45:20). That's right. It all happens when water percolates through those trees, and the decaying organic matter gets entombed to the silica. Those sediments are fantastic at recording individual microbial cells and you'd be astonished at the level of detail that paleobiologists can extract from these ancient sediments. There are other ways that we can detect former life on Earth. 

So you mentioned chemical analyses. We could use isotopes, carbon isotopes, in particular. That's because biology loves to use the lighter carbon isotope carbon 12, in preference to carbon 13. That's something that we can measure in ancient rocks, that we can detect. Then, of course, there's the presence of just organic matter that might have been produced by biological processes that could just get trapped in sediments. Silica aren't the only segments that can do it. Carbonate minerals that precipitate from lakes and seas are great at trapping this material as well. 

Both silica and carbonate minerals are actually present in the Jesero Crater, and then the delta deposits is great because the very fine grain sediments are good at trapping organic matter. 

We basically got some really promising environments…

SL. So they get stratified…

NT. Yeah, that's right. So if you go to fine grain deposits, lake deposits or marine deposits on Earth, usually, they are associated with, if they are deposited into the right conditions, high concentrations of organic matter.

SL (46:58). You're also looking at biosignatures, right? One of the biosignatures is methane. There have been detections of methane on Mars, it looks like methane is seasonal. So there must be either some active production of methane from the geological sources or organic sources or maybe there are some deposits from where the thing gets in and out from time to time. So I understood that the geological sources can be of two types. One of these is related to organic matter, but there is also one that has nothing to do with the organic matter and that's related to serpentinization. So I'm not a geologist, I don't know much about that, but I understood that there’s olivine on Mars. How is that related to serpentinization and how is serpentinization relevant to abiogenesis or support of life?

NT (47:57). Yeah, yeah, that's a good question. Methane detections in the Martian atmosphere have been an exciting and controversial result for the reason you mentioned. Life can produce methane but then rocks can produce it too. So it would be good to know what's happening. Unfortunately, the atmospheric methane detection is difficult to pin down, we don't really know where it's coming from, and we have very little information about what's producing it. 

My personal point of view is it's difficult to know what to do with that information. Given the quantities produced, it's likely that geological processes are to blame. The process you're referring to that can produce methane is called serpentinization. That happens when water interacts with minerals that are present in igneous rocks, the most important mineral being olivine, which is an iron-magnesium silicate, and there is tons of olivine in the Jesero Crater. It's in the surrounding regions, the surrounding geology. It's one of the things that makes the region so unusual on Mars, it is potentially the largest concentration of the mineral olivine on the planet.

SL. Even there…

NT. Yeah, we've known this for years from orbital mapping. There are a lot of different ideas about what it represents. Are the olivine grains sort of broken down and mobilized from igneous rocks, and they're now sediments or is it one large concentration of an igneous rock that formed from some extraordinary process? But as you mentioned if water interacts with olivine across a range of temperatures, you produce serpentine minerals. 

Then the other thing you produce in this process under the right conditions can be hydrogen, and then sometimes that hydrogen can react to make methane. That ends up being very attractive for early Mars for two reasons. One is that hydrogen is very useful for microbial life. It's basically a pretty high density energy source. So it doesn't take much for microbes to take hydrogen, which is a source of electrons and react it with something that wants electrons and to gain energy from that process. But the second reason is that hydrogen, we think, could have been key to warming the ancient Martian atmosphere. One of the great puzzles about early Mars is that there's all this evidence for liquid water and water moving around and shaping the earliest surface. But what we know about the composition of the Martian atmosphere is never really been clear how the surface of Mars got at temperatures beyond the melting point of ice or melting point of H2O.

SL. Which is different from the melting point [of ice] on our planet, because there is a different pressure. Was the pressure [on Mars] similar to our pressure back then? That depends on the atmosphere, right?

NT (50:59). Yeah, yeah, exactly. We assume that the early Martian atmosphere was present in a significant pressure, maybe something close to pressures of the Earth's atmosphere today. For the reasons you say, if the pressures is too low, you're not going to stabilize liquid water. But the big enigma has been, what was it about the atmosphere that stabilized liquid water? How could you warm early Mars? It's actually really difficult to do. The reason is that 4 billion years ago, the Sun was less luminous and this is a problem for Earth too. A lot of Earth Scientists debate this point, a lot of people feel that the early Earth should have been covered in ice. At least at one interval, the Earth was there, at least ice sheets were present. But as far as we know, the Earth wasn't completely covered in ice and so something kept the Earth warm too. 

But with Mars, the problem was even worse, because Mars is farther away from the sun. So there was there was some feature of the ancient Martian atmosphere that at least periodically allowed liquid water to be stable. It wasn't until very recently, again, this is some work that came out of Robin Wordsworth's group at Harvard. They proposed that in a dominantly CO2 atmosphere, which is what we believe Mars's early atmosphere was composed of, if you have a few percent hydrogen, the molecular collisions that results between hydrogen and CO2, produce a warming effect and can actually warm the surface above the melting point… 

SL. How does that happen?

NT. It has to do with, with how those molecular interactions absorb infrared radiation and it wasn't something… well, it was considered decades ago, by a few researchers, but it wasn't really clear where hydrogen could be coming from on early Mars. One source could be serpentinization. So it's something to consider now, especially because we know there's evidence for water, there’s evidence for significant amounts of olivine and so we, Earth scientists, would infer that that process could have been important. So it would be exciting to uncover evidence of that interaction in all of the enriched rocks at Jesero Crater.

SL (53:33). Serpentinization is an exothermic reaction, which produces high temperatures…

NT (53:39). It can proceed across a broad range of temperature, anywhere from sort of the temperature of this room, upwards up to about 200°C, or maybe even higher. The great feature of these reactions is that they can yield substantial quantities of hydrogen. That's also an interesting aspect too. We can test the hypothesis that serpentinization was present by going and analyzing these olivine rich deposits and looking for ancient serpentine minerals, and then start to constrain the chemistry of the fluids that interacted and maybe evaluated hydrogen was ever produced.

SL (54:26). For the warming of the planet [Mars], there were also volcanic activities, there were impacts… because I mean, if you have an impact with a big object, that's gonna, I don't know, maybe that's gonna keep the planet warm for a while. It will cook everything up, if the object is large enough, and we have even evidence of huge craters from impact on Mars, right?

NT (54:49). Yes, that's right. So there's thermal energy that's associated with impacts, but then that there are also the effects that impacts have on this around atmosphere. So sometimes you can have components that are locked up in the rocks get released into the gas form after an impactor strikes, and that can create, a warm environment at least for a relatively short time, and maybe on the order of 10s of 1000s of years. So you could do it for short intervals of time. The issue with that is that there's geological evidence on Mars that liquid water was present for millions of years at a time. So impacts could have helped. And they could have maybe triggered some important changes in the state of the climate, but researchers now we're looking at other mechanisms that could affect longer term change.

SL (55:44). Yeah, because impacts are just a temporary, the effect is going to dissipate, then disappear.

NT (55:49). Yeah. Yeah. So volcanoes can help too. But again, it's not really thought that volcanism on Mars yielded substantial hydrogen. The reason why we think that is we know something about the redox state at Mars’ mantle, and it's probably not reducing enough but I know a lot of folks are revisiting that assumption.

SL (56:11). Ashes would have a negative effect in terms of temperature, that will reduce the temperature.

NT (56:18). Yeah, so there's a short term climate response when ash is thrown up into the atmosphere, it can actually produce net cooling, some of the sulfur dioxide aerosols that are exhaled from volcanoes can also have that effect. 

SL. But again it's short term.

NT. Yeah, yeah, that's right.

SL (56:36). Okay, now, I was looking at I think there was an article published in Science on the meteorite ALH84001. That's the famous medium meteorite that was mentioned by Bill Clinton in his speech, which was a bit controversial, because he was suggesting “Oh, maybe we found evidence of life on Mars”. But then it turns out in this paper that was a due to serpentinization.

NT (57:04). Well, yeah, or maybe a related process. That was an interesting time, I think, for folks that are interested in Mars, although it happened when I was in high school, I wasn’t quite…

SL. 1996…

NT. But it's still relevant now. It's an important lesson, to say the least. There was a team of researchers that studied the meteorite, and they thought they had multiple lines of evidence that microbial organisms left imprints in that meteorite. The lines of evidence included certain types of organic compounds, so polycyclic aromatic hydrocarbons, they are basically hydrocarbons contained of aromatic benzene rings, certain morphologies of minerals like magnetite, which is an iron oxide mineral, and iron carbonate. So all the lines together, they felt, presented a very strong case that microbes were present. As is the case in the scientific community “extraordinary claims require extraordinary evidence”. So the scientific community dug into those lines of evidence to ask the question, “Could all this just be formed by physical and chemical processes?” The short answer is yes, that there were rather simple properties that were identified that could form all of this associated with the just the impact that produced that the ALH meteorite and the process by which it landed on Earth.

SL (58:37). Which is bad for those clickbait news. Ancient Aliens. Do you remember that picture? The “alien” face on Mars?

NT (58:47). Yeah, I think so. Well, it came from one of the orbital images, right, and was it a little bit doctored and then kind of circulated in the media.

SL (58:55). That was an effect from the shadow. I mean, you can see any sort of things from clouds, rocks… 

NT (59:00). Oh, yeah, there's plenty of data, you'll find what you're looking for if you stare hard enough.

SL (59:04). Why people believe weird things? There are actually people that think that there is no International Space Station, we never we never went to the Moon, the Earth is flat, and all these things. Why do you think believe does weird things? Is it because of ignorance or because they can't possibly understand what's going on?

NT (59:25). I think … I don’t know…

SL (59:30). It’s probably realm of psychology rather than science.

NT. Yeah, that's right. 

SL. I'm sorry, I didn’t want to offend psychologists… I meant hard science.

NT (59:37). No, that's right. I mean, I know that there are lots of underlying reasons probably why folks hold up these opinions, it's beyond me. I find it interesting as to why people think the things that they do, but they seem to be a pretty, pretty small, but sometimes vocal minority.

SL (59:55). So if you encountered one of these folks in a pub, what would you tell them If they told you “There's no Perseverance robot on Mars. It's all fake”.

NT (1:00:04). Yeah, I mean, you know, sometimes you can't really change these strongly held beliefs. And so, you know, the best you can do is just, you know, discuss the evidence as you see it in an objective way. If folks choose not to believe it, then that's, that's their decision.

SL (1:00:23). One of the things I was trying… because I was having chat with this guy, who was claiming the Earth is flat, and all these things. I was trying to tell him, “Look, there is no way they can fake all this data, there's so much data that they would need to pay 1000s and 1000s of people to fake on this data, it's not something that is possible”. And also we don't have the capability to simulate all these things. The way we can simulate things is very, very limited. In fact, I was thinking about, Okay, can we simulate those early conditions on our planet? Can we put just all those basic molecules together and develop some molecular dynamics model that uses the Schrödinger Equation and tries things and put the initial conditions with the geology and the atmosphere and all these things? Can we let it evolve? I don't think we have the capabilities for doing that.

NT (1:01:19). No, but what you're what you're getting at is, I think, the next sort of frontier for origins of life research, right? 

SL. Simulations. 

NT. Yeah. So there's been all this exciting evidence coming from organic chemistry laboratories. We know a lot about early environments on Mars and planetary processes that shaped planets early in their history. We know a lot more about early environments on Earth from theoretical studies. So this is a great way to test some of these ideas by adding those ingredients together, and running experiments to include that element of complexity that's difficult to know, beforehand. Especially folks that do a lot of experimental work and geochemistry, myself included… there are great sort of hypotheses that can be tested by going to the laboratory and combining elements of organic chemistry and geochemistry, and seeing what works and what doesn't.

SL (1:02:21). Yes, so that's involving experimental, but what I was talking about is just simulations, molecular dynamics. So you start with the Schrödinger Equations describing the atoms, and then you try to build these huge models. What I was trying to say is that, I don't think we have capabilities for doing that on a large scale. We can do that on a small scale. But I don't think, I don't know, maybe you know something different… but I don't think we can synthesize things like a ribosome from scratch using simulations. Can we do that?

NT (1:02:54). No, you're right, there's a limit. So the molecular dynamics calculations that you're talking about are computationally expensive, they require a lot of resources. So the size of the system that you can deal with is necessarily pretty constrained. Yeah, it would be great to expand that to much more complex and larger scale systems. That’s certainly beyond the current frontiers of that technique. But there are people at Cambridge, Alex Tom's group, for example, there are molecular dynamicists, who are interested in these questions, and those computational methods can be really important especially in accessing regions of chemical and physical space that are difficult to access in the laboratory. So there's real value in that approach as another component towards addressing the questions we've been talking about.

SL (1:03:51). If that was possible, we could think of a scenario in which we tried so many different paths and initial conditions and boundary conditions, and we let the system evolve and see what we get. And maybe we're gonna end up getting some simulated precursors of life, maybe DNA, RNA, ribosomes, whatever, that would be amazing. So maybe with the quantum computers, who knows, right? 

NT (1:04:20). Yeah, reminds me there's this great cartoon from the New Yorker that came out years ago. It's a picture of a chemist’s laboratory bench with all kinds of complex equipment. At the very end of the bench, there's a beaker and this this slime in the beaker pops his head out and ask the scientists “Are you my mommy?”

SL (1:04:38). Yeah. So another thing of testing how life might have emerged is running experiments in the lab. You mentioned John Sutherland. But another way of doing experiments would be, Okay, I build a small world with geological and atmospheric conditions. I put my basic ingredients and let it evolve. So what do you think is wrong with that model? Or do you think that's the right way of proceeding?

NT (1:05:07). Yeah, one difficulty is timescales. Right? We're interested fundamentally in geological processes. We're only humans, we can only sit around and watch things for so long before we get bored, or before someone's PhD is over. What we can do is we can investigate certain components of systems over time, but in order to really understand how they evolve, you know, across geological time, I think that's where we need to resolve to observations. Sedimentary rocks on Mars, for example, can give us information about how climate responds over millions of years. But then also computational methods. There are ways of calculating climate responses and the response of the oceans, over millions and millions of years. And, you know, that that's the best we can do at the moment.

SL (1:06:09). Because attempting to do what I was saying will take forever. 

NT (1:06:15). Yeah, but we can, if we have a hypothesis that involves different stages of evolution, we can go in and examine the different stages and sort of trying to understand it from a series of snapshots and try to figure out how the stages related to one another.

SL (1:06:32). You got some slides, you wanted to show me something? 

NT (1:06:36). Oh, yeah, I just, I threw together some things. It sort of depends on what you might want to what you might want to look at. Oh, yes, this is just a timeline of important events in the history of life on Earth. It sort of starts off with underscoring the point that if you're interested in the origin of life, you really have to go pretty far back in Earth's history. We think that the key window was probably sometime between, say, 4.3 billion years and, say, 3.6-3.7 billion years. Unfortunately, there are very few rocks and minerals from that time period. So to access that time, this is what we've been talking about today, you have to, theoretically, go somewhere else like Mars, where at that same time there were environments that might have been similar to environments that could have hosted the origin of life on Earth.

SL (1:07:42). This is a visualization of the plate tectonics…

NT (1:07:45). Yeah, a geological map of the Earth. I used this in a talk to underscore the point that the reason we have few samples that archive that time period is because of plate tectonics. And you can see plate tectonics expressed beautifully in this geological map of the Earth, you can see the mid oceanic ridges, the effects of plate spreading, and also the complicated nature of the continents, small sort of slivers and pieces of ancient continents sort of plaster together and deformed.

SL (1:08:19). What's the color map?

NT (1:08:20). So the color the color refers to ages. You can see that large swaths of the mid oceanic Ridge are similar age and that's because of the plate spreading effect.

SL (1:08:36). So red would be what, old or new?

NT (1:08:39). The age scheme here is relatively complicated. I think the pink and purple colors represent some of the most ancient terrains on Earth. So in particular, the Canadian Shield. So if you look in northern Canada, there's a large swath of pink.

SL (1:09:02). And Greenland as well you said it’s very old.

NT (1:09:04). Yeah, that's right is Greenland around the edges, where it's not covered in ice. Western Australia. There's a very large swath of pink which represents the Pilbara Craton,

SL (1:09:15). Sardinia is very old. I knew that.

NT (1:09:20). Yeah, and the interior of certain parts of Africa, and South America. So these are some of the remnants of the oldest pieces of continental crust on the Earth. But they've experienced such a complicated history that the sedimentary rocks that are there are pretty highly deformed.

SL (1:09:41). And this is the map of Mars…

NT (1:09:42). Oh, yeah. This is a type of geological map on Mars. It's really just highlighting the age of the very very ancient rock. The brown colors correspond to rocks that are on the order of 3.5 to 4.2 billion years old. That's sort of the key window that we would like to know more about when we are asking questions about the origin of life. And you can see that there's a huge fraction of the planet mostly in the southern regions, where rocks that old are still accessible at the surface. And many of those rocks are sedimentary in nature.

SL (1:10:19). That’s the tallest volcano in the entire solar system, right? 

NT. Yes. Olympus Mons, 

SL. 20 kilometer, so how tall is?

NT (1:10:25). Yeah, yeah, it's about that. It's roughly the size of the state of Arizona, which I guess Americans will, well understand. And that was always the analogy that stuck in my mind best.

SL (1:10:41). So I was reading a paper mentioning the [most recent] active volcanos on Mars was, like 53,000 years ago or something like that? Oh,

NT (1:10:50). Yeah. There's evidence for quite young volcanism. That's right.

SL (1:10:55). Are we absolutely sure there is no activity? Is there any way to verify that?

NT (1:10:59). You can see it expressed I guess, in two ways, there's a mission that monitors the composition of the atmosphere. If there are events that exhale volcanic gases, if it's significant enough, that might be detected in some regions by that instrument. 

Then another is orbital imaging and mapping of the surface. If there are fresh lava flows, which is the evidence for the most recent volcanism, then you might see it.

The way that we know the age of rocks on Mars is kind of tricky, because we don't you know. On Earth, as I mentioned, we could use things like uranium-lead dating and that. But we can't really do that with Mars. And so what a lot of scientists do is they use cratering statistics. So there's an idea that the flux of impactors to the Moon, Earth, Mars, and basically, the terrestrial planets, has been roughly similar over time and that earlier on, forward to 3.5 billion years ago, there was a very high flux of impactors, and that's tailed off significantly over time. So, you can plot then the frequency of impactors as a function of age. So if you have a terrain and you count the number of impact craters that are there, it can give you a statistical constraint on what the age might be. Another way of saying this, is that the oldest regions on Mars are pretty heavily cratered and the youngest regions don't have very many craters at all.

SL (1:12:49). A comparison between the ages. What do you call them? Eons?

NT (1:12:51). Yeah, that's right. This is a comparison between the geological timescales on Earth and Mars, and then just a rough schematic of important events that happen on Mars. I mean, without going through them all in detail, you can see that all the action on Mars happened early and then things got pretty quiet for the last few billions of years. 

These are locations where sedimentary rocks are present on the surface of Mars. The white and black points are areas that sedimentary rocks have been identified or inferred by orbiting imagery. And then those seven yellow points are areas of sedimentary rocks that have been investigated by landed missions, or in a significant detail where we actually know a lot more about the sequence of those sedimentary rocks. This is something that came out of a paper that my PhD advisor wrote that I was part of, and a couple of other collaborators that sort of summarized what we know about sedimentary rocks on Mars, there are quite a few of them.

SL (1:14:05). There is also a simple retrieval mission. You are heavily involved in that. The plan is to send the samples that we're collecting now back to our planet. How are we going to do that?


NT (1:14:18). Good question. So what Perseverance is doing is it's, it's drilling cores, and you know, we will end up with about 35 or so cores from different places that we think represent the best possible samples that are worthy of being returned to Earth. Those will be deposited on the surface left behind. And then two subsequent missions will be launched to collect those samples and bring them back to Earth. The way this is proposed to work is that the first mission after Perseverance is something called the Sample Fetch Rover, which is just a small basic rover, that will land near where Perseverence landed, roundup all the samples, and place them in a vehicle that will be launched into Martian orbit that will contain the samples and basically a thermal and shockproof container. That vehicle will orbit Mars, and then a subsequent mission, an orbiter will fly to Mars, rendezvous that vehicle, slingshot around the Martian orbit and returned to Earth and then drop the vehicle into Earth's orbit. And it's planned that that sample vehicle will land on Earth, hopefully within about 10 years’ time.

SL (1:15:44). So around 2030 something. Yeah, but why don't you just ask those guys that are going to Mars to just go there, collect the samples, and then bring them back? Because we're supposed to send humans to Mars? Right? So wouldn’t be easier if we are really sending humans to Mars… do you think it’s happening?

NT (1:16:07). There's some discussion about human space exploration. And I mean, my views on that are mixed. As a scientist, I think it's a far better use of taxpayer money to invest in remote and landed missions, as we've sat around and talked about today, because the scientific advances that that's enabled that have been huge. The engineering activities that have gone into engineering components and instruments that are associated with those rovers have spun off and produced all kinds of benefits to society. Human Solar System exploration will always be attractive to the human race, because it's in our nature…

SL. To explore things…

NT. Exactly, yeah. However, it's expensive, and it's risky. And although it would be exciting to sort of see that develop in a few years, in the next few years, one can also think of lots of other things that we should be spending our time and money on here, here on Earth.

SL (1:17:15). Well, we spend money with things that some people would think “this is a waste of money”. We spent money in wars, for example. We could dedicate that money to a manned mission to Mars instead of going and attacking other countries, which is probably better, and maybe the folks from the military-industrial complex would make their profits, which I mean… they're [already] contributing to these missions as well. There's Lockheed Martin, which is heavily involved in this. If we work on a manned missions, maybe we'll come up with some solutions that will benefit society. That even happens in wars. If you think about the military industry, we got innovation and things that benefitted us. The Internet for example, it was developed by DARPA. The microwave was developed by Raytheon. So who knows? Maybe we'll come up with some solutions by sending humans to Mars. 

But the other thing is that if you send humans, they're gonna do these experiments much faster than a rover? Does that make sense?

NT (1:18:34). Yeah, yeah, that's right. I mean, geologists can go through and walk up to walk up to outcrops collect the rocks, do what you need to do in a few hours a day. 

SL. Instead of a year.

NT. So to walk over the other side of the room and collect a sample would take us a few minutes. You know, to the rover, it takes days, weeks…

SL (1:18:53). One of the other targets of the Perseverance Rover is production of oxygen in situ. Are you aware of any of those problems?

NT (1:19:06). Yeah, so I guess, a little bit of background about that instrument. So it's called MOXIE instrument. Its purpose is a technology demonstration. There's a really clever idea that was put together by scientists and engineers who developed the MOXIE instrument, which is that oxygen could be produced from just atmospheric components that are currently on Mars. So it's electrochemical oxygen production. What they did is they developed a small device as a proof of concept that this could work. The purpose of this instrument is to collect information about the efficiency of that process and to demonstrate that it can work and as far as I know, it's been successful. So it's an interesting step towards exploration and evaluation. As you know, the feasibility and efficiency

SL (1:20:02). So it is already up and running?

NT (1:20:05). Yeah, they've already conducted a few experiments that have been successful in the mission. 

So this is a map of the different types of mineral groups that are present on the surface of Mars. It is really helpful because it tells us information about liquid water. And there are also just a couple of places highlighted for reference. So Meridiani Planum, was the landing site of the Mars Exploration Rover mission that I was involved in 2004-2005.

SL (1:20:41). The one that we were referring to before in terms of water salinity. 

NT (1:20:45). Exactly. And you can see this cluster of purple triangles there. Those are sulfate minerals. Those are the salt minerals. And you can see that those sulfate minerals are distributed along a specific area that includes Meridiani Planum and some regions westward. And then Gale crater was the landing site of the following rover mission, which is the Mars Science Laboratory that launched in 2012 and is still operating. So it's been operating for 10 years. And it went to Gale crater, which is the site of another lake system where sedimentary deposits are recorded. And there's such a significant sequence of sediments that you can actually sort of get some insight into what's happened over a very significant length of time and that's what the Mars Science Laboratory is working on now.

SL (1:21:45). So this is a basically getting a map of this soil on Mars. But one thing that was reading is that the soil of Mars toxic. It's unsuitable for life. Have we done any experiments on that?

NT (1:22:01). Yeah, that's a good question. I mean, so this is this is telling us a little bit about soil and just exposed rock surface, but soil is maybe not so great, because it's dry, it's very fine grained, and usually with very, very finely crystalline silicate minerals, especially, we know, from our experience on Earth, that when you inhale that fine dust that actually does bad things to the lung fluids.

SL. Silicosis. 

NT. Yeah, exactly. So it produces free radicals, reactive chemical species that break down…

SL (1:22:34). Which is the same issue with the regolith on the Moon.

NT (1:22:37). Yeah, yeah, that's right. So that's part of it. For reference, I don't have it labeled on this slide. But Jezero crater is underneath of the word Gale, there's a cluster of green circles, which corresponds to carbonates… that's it? Yeah, that's where Jezero crater is.

SL (1:22:59). Did the Chinese send a rover to Mars? 

NT. Yes, they did. 

SL. Where did they send it? They are not very open in terms of… NASA is very open in terms of outreach and showing goes this images, but I was searching a website on the Chinese robot, and I couldn't find anything. Maybe I'm not good at searching.

NT (1:23:24). Yeah, I guess they might have different restrictions in terms of what’s released and when it's released. But yeah, I unfortunately, I’m in the same sort of position, we haven't really heard as much sort of detail of the findings. But again, it's a different type of mission. It's a landed mission. It's not a roving mission. So staying in one spot, conducting a series of experiments. 

SL (1:23:47). Is there any collaboration going on between… because this mission is led by the US basically, is there any kind of collaboration going on with China? Or we're back to the space war? Which was good, by the way, because that created competition. When there is competition, people tend to do things that they wouldn't do otherwise. Well, what's the situation? Is there any collaboration going on or it’s all competition?

NT (1:24:13). For example, the Mars sample return those missions that I talked about, there's an agreement between NASA and the European Space Agency, that that will be a joint effort and those missions will be shared. And I think in due course, both of those agencies would probably welcome additional partners, like China or India, for example, in time, but politics and global economics is sort of determine the nature of that collaboration.

SL (1:24:44). Because you would have the facility already in place… It's already being built… the retrieval facility…

NT (1:24:51). It's being built now. So what we did, we're part of a committee, an international committee of scientists that try to take the planning from our sample return to the next step. So what are the things we need to think about, how the samples might change and their character, their chemical or mineralogical character from the time that they're collected to the time they land on Earth? What are the key instruments and capabilities that need to be in the sample receiving facility? What types of instruments? What are the analyses we need to do immediately? What are analyses that we can do later? How do we get the global scientific community involved? What's the fairest way of inviting other scientists to work on the samples? How do we make that process transparent and open to the rest of the world? So those are some of the big issues the committee was concerned with that resulted in a series of publications, where we just communicated our findings to the rest of the scientific community to generate discussion. But it was a fun process. We thought about a lot of issues that we didn't think about before. Now we've got a really specific set of recommendations that are going to be handed to the engineers that are building the sample return, receiving facility. 

SL. Where is it? 

NT. I think the exact location is still uncertain now. But one idea is that the sample receiving facility might exist in the US. Another is that there may, in fact, be two, and there could be a sample receiving facility in the US and then one in Europe as well. So the location is still being worked out. But the capabilities, the scientific capabilities, were what we were concerned with.

SL (1:26:45). And you're building a biohazard level 4 facility, which is the highest standard for biological contaminants. What are you worried of?

NT (1:26:55). Yeah, so I wasn't involved in this part so much specifically, but I guess if we open up samples that come from Mars, I mean, we have Martian meteorites, for example…

SL (1:27:08). Those just arrive and that's it…

NT (1:27:11). Yeah, there’re pieces of Mars that have landed on Earth since Earth is has been formed. But these samples are different. We have the meteorites, but these samples are gonna be different. They're potentially soils, sedimentary rocks. And we just have to do due diligence in terms of protecting the public about any…

SL. … potential pathogen…

NT. Yes, any risk at all. It’s the responsible thing to do. So that's the reason why the biohazard controls are in place. Because if microbes are present and if they pose a risk, it would obviously be a disaster if that was managed and controlled properly.

SL (1:28:01). In fact, it's also possible that the microbes could be hibernating… things like… that happens in our planet. 

NT (1:28:09). Yeah, that's right. So yeah, microbes have the capability to go dormant and basically arrest most of their metabolic activity and then start it again, under different circumstances. It would be interesting to ask whether or not any microbial life would have adopted the same sort of capability. I mean, I guess what we've talked about is this story of water being on Mars, but being intermittently present. And so maybe that would drive the need to cope with intermittent dryness and needing to go dormant.

SL (1:28:46). We also have organisms on our planet that can survive almost in vacuum… I think they did an experiment on the International Space Station, where they put outside this little warm. I forgot the name of it, but it's super resistant, and it survived. I'll have to check that, I'm not 100% sure, but I think there are living organisms that can survive in extreme temperatures, extremophiles. 

NT (1:29:12). Yes, that's right. I guess one thing to say about extremophiles is that on Earth, we have almost every conceivable environment, we've got hot environments, cold environments, salty, dry. And life on Earth has been present for at least three and a half billion years. And life has devised a number of clever adaptations to these environments. So life now… I would never be surprised by what microbial life on Earth is able to cope with. But those are traits that are required from billions of years of evolution. And so when we think about extremophiles and microbes being able to cope with different environments, we have to kind of keep that in mind. These extreme environments might be okay for Earth-based microbes, but for early life on Mars, It's more of a question as to why their life would adopt those traits or not…

SL (1:30:03). Because they didn't have enough time to evolve.

NT (1:30:09). Yeah, so these are just images of some of the sedimentary rocks that were analyzed by the MSL mission. So you can see the finely layered structure in the sedimentary rocks. Then there's a schematic of how all those rocks fit together, in order of oldest to youngest. So oldest at the bottom and youngest as you go upwards. It's been quite a detailed and amazing set of results that have come out of the mission over the last 10 years. It's basically a valuable environmental archive. So how the environment and that location the planet has changed during that interval of time.

SL. I think I’ve seen this in a paper.

NT. This is a schematic of that environment, at one period and its sun and its history. So based on the information returned from those sedimentary rocks, the MSL team proposed that there was a lake present, but that lake actually had very redox states. So the deeper waters were dominated by reduced compounds, and the shallower waters received more oxidizing compounds. That's hugely important because that could be important to ancient microbial life. And those different environments are reflected by the minerals that are present in the sedimentary rock. 

So for example, at the very bottom of the lake towards the center, you can see what's called magnetite, silica facies, so there's a large concentration of the mineral magnetite, which we know you can form through reduced iron. 

This is a schematic, again, from Robin Wordsworth's paper of how the ancient Martian climate might have operated. This is an interesting hypothesis that's based on years of climate modeling that Robin and others have done. The idea is a relatively simple one. It starts by observing that the there's a big difference in the topography in the south versus the north. Remember, we talked about this. That can actually be very important, at times of high atmospheric pressure. The idea is that when atmospheric pressure is very low, temperatures on the surface will vary with latitude. So in other words, the warmer temperatures will be towards the equator in the colder temperatures would be towards the poles. 

But if, for some reason, the total atmospheric pressure increased, then the warmest temperatures would actually be the lowest lying topographic areas on Mars, and the highlands would actually be very cold. So he proposed that if there were intervals of time, where total atmospheric pressure increased either through impacts or volcanism, that would set up a climate where the Southern Highlands would be characterized by snow and ice and the Northern Plains would be characterized by liquid water, and there would be exchange between those two environments. The reason why that hypothesis is attractive is because it works from a climate perspective but also it's consistent with geological evidence. So most of the locations of lake deposits that we know about, coincidentally occur right in the boundary between the Northern Plains and the Southern Highlands. 

This is just the sort of showing that. So the white dots are all open basin leading deposits. And you can see that they sort of they sort of lie right around the boundary between the blue areas which are the low lying Northern Plains, and the red warmer colors, which are the southern islands. 

Yeah, and that's just a picture of Jesero Crater landing site. That's right, colored by a dominant minerals that are present in these different deposits. 

That's the sample collection facility.

SL (1:34:29). Did you have a chance to go there and see and help when they were mounting the instrument?

NT (1:34:35). No, no, I didn't. I mean, keep in mind that most of the rover was built during the pandemic. It an absolute miracle that they managed to get it built, get it to the landing pad and successfully land it. I mean, if that wasn't hard enough, having to deal with it, the working conditions of the pandemic made everything much harder. 

SL. They are dressed up like because they want to protect Mars from our bacteria.

NT. That’s right. 

SL. How do you sterilize the rover?

NT. So I don't actually know the details. I think it's multiple stages of sterilization, that involve a thermal sterilization mostly. So I think a lot of these components are baked down in the oven. 

SL. Ah, like when you bake vacuum chambers and stuff like that?

NT. Yeah. Yeah. 

That's a geological map of the Jesero Crater. So you can see the landing sign in black, the delta deposits in blue, and the crater floor in that sort of pale in salmon color. And that's been the area that we've been working in mostly is sort of the boundary between that salmon colored unit and the pale colored unit.

SL (1:35:54). All those dunes, there is sand in there. Is it due to erosion of the rocks? Wind.

NT (1:35:59). Yes, that's right. 

SL. So I don't want to walk there… you don't want to go there with the rover, right? 

NT. No, yeah. Previous rovers have gotten stuck in sand and it takes a long time to get them out. So the folks who drive the rovers there's no way that they'll drive it into sand, we have to go around. And there are some big dune fields there.

SL (1:36:19). You can't get help from people putting platforms under the wheels, right?

NT (1:36:23). That's right. And that's another image, that's just sort of zooming in and the area where the rover landed. So you can see the landing site and the blue point. Yeah, Octavia E. Butler Landing Site. We went south along that yellow dashed line, and investigated the boundary between these two geological units. The idea now is to circle back around and now that we're mostly finished that campaign to hightail it toward the delta. So you can see the edge of the Delta just there in the left. 

SL (1:37:01). And there's no way you can cut through because there are sand dunes there.

NT (1:37:05). Yeah, so the easiest way would be to go around. But the rover, because it's got this autonomous hazard avoidance capability, it can actually, as far as rover go, it make quite a bit of progress day to day. So now is the time when we're wanting to get to the Delta deposit as quickly as possible.

SL (1:37:28). We haven't spoken about the there's a drone as well. 

NT (1:37:33). Yes. Ingenuity. Yeah, that's right. It was only supposed to successfully complete a few flights. And they've done… I've lost track of how many they've done. Now, it's just been enormously successful, like most things that that NASA has done when it comes to Mars exploration is just so well engineered.

SL (1:37:54). That's the hole that you were mentioning before…

NT (1:37:57). yeah, that's right. So this is an example of some of the rocks that we first analyzed in the crater floor. In the left hand side, you could see that abraded patch. And then later on, after we studied that abraded patch, the idea was to collect a sample by drilling into the rock. So we study what the rock is made of, we sort of characterize it, and then we collect a sample, not in that exact spot, but somewhere close by, and accepting that it's the same material. And this one was interesting, because with the first core, you probably heard about it. It was, well actually, if you go to the next slide, I think there's an image…

SL. Like where is this sample? 

NT. Yeah, that's right. So this is the image that came back. The sample tube is empty. And it's set in motion a whole series of investigations as to what happened, whether it was an engineering component malfunction, and turns out the rock was just too crumbly. And so if you go to the next slide, there’s a great nighttime image taken of the hole and all of the remaining abraded… it just got obliterated to fine particles. That was pretty interesting because that rock has seen a fair amount of liquid water and it's that interaction with liquid water that resulted in the rock having those physical properties. 

Yeah, this is some detailed work that we did with the SHERLOC instrument and PIXL instrument and another instrument called SuperCam, which fires a laser targets and takes advantage of the excitation of atoms by the laser and can determine chemical composition. But these are the areas that we focused on these rocks, and I think the next slide is yeah, just some pixel…

SL (1:39:54). That’s the kind of maps you can get with your instruments. Okay.

NT (1:39:57). Yeah. And I should say that these are only a few of the chemical elements that we can analyze, but the data visualization software and what we're able to do with these data is just incredible. 

SL. This is public domain, right? 

NT. Yeah, these were images that were released on the JPL website, I think. But you could see on the left hand side, iron, aluminum and chlorine. So there are some areas with high chlorine in the right hand side, we're looking at sodium, sulfur, and chlorine, and you could see that the sodium is in red. On the right hand side, chlorine is in blue. And so the mixing between the two make purple. And so there was there are minerals there that are dominated by sodium and chlorine. We thought initially, they might be the mineral halide, which is you know, what constitutes table salt, but actually, it might, we think now, from data from the SHERLOC instrument that it might be oxidized chlorine. So perchlorate, sodium perchlorate mineral. 

SL. That’s a selfie.

NT. That rover takes these selfies where it rotates the arm and takes these panoramic images and it creates a beautiful mosaic, but towards the bottom, you could see one rock that actually has to drill holes in it. And that's where we finally ended up successfully collecting samples from a target rock named Rochette. 

Oh, yeah. So you asked about fieldwork before about, you know, some of the work that we do as geologists, I think I mentioned that some of the work we do involves understanding how, you know, how Earth's oceans have changed in their composition over time…

SL. I’m getting cold [looking at that video]

NT. Yeah, yeah, in the past, we've gone to areas like Svalbard and the Canadian Arctic to really understand that. 

This is just a short video, actually, that I took on an ice cutting sailboat when we're in the Arctic. It's a fantastic place. This is up in Svalbard. And we're actually leaving to go home at this point. This was a couple of years ago in early August. It was already getting stormy. So…

SL (1:42:21). That looks like a small boat.

NT (1:42:23). Yeah, it was a 45 foot sailboat. It was a pretty amazing way to do fieldwork, because you could just sleep on the boat and not worry about polar bears. But the next few images 

SL. Did you carry guns?

NT. We had guns. Yeah. Yeah. It's just for safety. I mean, you try everything else first. 

SL. Because you are food for the bears. The little ones are cute. But the big ones…

NT (1:42:43). Yeah. And we didn't see a big one. I think I've got an image or two after this. That shows one we saw. Yeah, that's him. He swam out to the boat to the pool. That morning, we had cooked a big breakfast, bacon and eggs, because we're out working late the night before, because at that time in the Arctic in the summer, the sun's up all the time. So you can just work late and we're exhausted. So we just did a big breakfast, which is not a good move. Because probably every polar bear within miles smelled that and came running. This guy swam out to the boat, you can actually see he's got a tag in his left ear. So the wildlife organizations out there usually like to track poor bear behavior, because obviously they're endangered. Well, their habitats are endangered and their population is suffering pretty severely. But once they are interested in you… I think we just decided we needed awesome food. And we just decided we needed to leave. Because I didn't think he was gonna go away. 

Yeah, it was an incredible, incredible opportunity to see one an in person. I think I just included two more images of that one polar bear. So that's him getting out and sitting on the coast and watching us intently. And then he was sort of following us. And after that we just left. We left for about two three days and came back to the area and he was gone.

SL (1:44:22). Okay, so you are part of this bigger initiative. How's it going so far? What's your role in the initiative?

NT (1:44:32). Yeah. So this initiative called the Leverhulme Center for Life in the Universe.


SL (1:44:37). Is it the only initiative in in Europe? In the European Continent…

NT (1:44:48). There are other initiatives that are interested in questions of this type, but I think this is potentially one of the biggest. So we just received a grant from the Leverhulme Trust of £10 million for 10 years to establish an interdisciplinary research center. 

The goal of the research center is to develop a more robust understanding of what life is, how it originated on this planet, and where else it might exist in the universe. When I say anywhere else in the universe that includes the rocky planets and other planetary bodies in our solar system, but also includes exoplanets. That's been one of the other exciting discoveries concerning questions of the origin and distribution of life in the universe. 

So that's led by Didier Queloz in astrophysics. He's the Director of the center. I will fill the role of Associate Director. It'd be really fun because it includes researchers and astrophysics who are interested in characterizing exoplanets. So there are folks involved in the James Webb Space Telescope, for example, that launched last Christmas and prebiotic chemists. So John Sutherland is part of this, his group and other chemists at Cambridge, as I mentioned before, and then folks in Earth Sciences, so myself, and others who are interested in understanding how planets are formed and how they evolve as systems and how their surfaces might facilitate life. 

It's a really exciting opportunity and it wouldn't have been possible without Didier, kind of having this vision and getting everyone together. Even more than that everyone just got so excited by it, that we really put our all into the proposal. I have really great hopes for what's going to come out of it in the next few years.

SL (1:46:52). Because under normal circumstances, it's a bit hard to get funding if you have people from different fields, right?

NT (1:46:58). Yeah, that's right. For this type of work, especially right, because it doesn't fall very neatly within the confines of the research councils that normally disburse funding. All of us write proposals to NERC, the Environmental Research Council to do with Earth Sciences and environment based research. But if you want to seriously pursue questions like this, it's difficult to find funding for it. And that's where philanthropic organizations like the Leverhulme Trust really enable big changes and our understanding of these problems.

SL (1:47:36). What's the ultimate target for the initiative? What do you expect to achieve in 10 years’ time?


NT (1:47:42). Yeah, I think I think in 10 years’ time, I'd really like to see Cambridge, kind of leading the conversation on what constitutes life, the capacity of planetary systems to support life. And I think the other side of this is that because this is such a big interdisciplinary center, and because we have so many different physical scientists and scholars from Arts and Humanities involved,   we feel that there's an opportunity to train the younger generation to think differently in order to really tackle questions this complex. So hopefully we can cultivate a new generation who can really redefine our understanding of life and where it exists.

SL (1:48:29). And I think that component, it's something that is usually rare when there is a scientific research going on, to involve the philosophers, the Humanities aspects. 

NT (1:48:43). That's right too. There are some really important and interesting aspects of this. Simply by asking the question, What is life? What do we mean by life? A lot of times, we can bring in a bias or preconceived notions about what we think life should be. If we're really serious about understanding where else life might be in the universe, we have to abandon some of those and maybe think about it a bit more broadly and more objectively, and that's where folks from philosophy and divinity can really help us do that. So we're really excited about those interactions.

SL (1:49:22). Okay, Nick, thank you very much. 

NT. It's my pleasure.

SL. I learned a lot from all this discussions about Mars. So I wish you all the best for this initiative. 

NT (1:49:36). Yeah. Yeah. Well, thanks a lot. We'll, we'll keep you updated with how it goes. 

 [SciVPro1]It’s 2008