Erin: Thank you so much for taking some time today, Levben, to, co-create a drawing of the work that you did on the paper titled Sulfur and Martian Magmas from Sulfur Concentration at Sulfide Saturation Applied to Regional Chemical Maps .

Levben Parsons: It's quite a mouthful.

Erin: Off the top of your head, do you have an idea of what you would rename it to?

Levben Parsons: No, but probably you know, simple like 'Sulfur on Mars' or, but that's kind of basic, you know, I think a good title is something that's like descriptive and I think that this title is very descriptive, but it probably only means something if you know what those words are.

I always trip up over those words like sulfur concentration, it's sulfide saturation.

It's just like too many s's, too many c's all at once.

Erin: Can you tell me a little bit about your background and how you found yourself studying the surface of Mars and volcanoes?

Levben Parsons: Yeah. So my background is in astrophysics, actually. And I spent a lot of time as an undergrad studying galaxies and dark matter.

And after college, I sort of pivoted and went into education because I quite frankly thought that physics was just like too difficult for me. But after spending a little bit more time sort of reflecting, and sort of easing back into the world of research, I realized that what I needed was something that was more concrete.

So astronomy, studying galaxies, something like dark matter... it's such an abstract concept. And something like volcanoes... rocks and minerals, and all of these Earth based things are just so much more concrete. Like I can go out into the field and collect rocks and tell pretty good story-- can't quite do the same thing for galaxies. So I think I gravitated towards this program and Mars in particular because it is a lot more concrete, but still a little out there. Like we can't actually go to Mars. And I think Mars is incredibly enigmatic. We have a lot of technology there. 

Erin: Yeah. 

Levben Parsons: And I feel that it's a great place to find answers to some of those big questions that we all have about whether or not we're alone. So, I think Mars, just by the fact that it has so many missions there currently, it's a great way for me to sort of like... gain some experience within the realm of planetary science. In fact, I'm working on the Dragonfly mission right now.

So, it's a great step into this project that's even more out there, but has, I think, an even greater possibility for finding evidence of biotic chemistry that I think could potentially lead to us answering some of those big questions about life.

Erin: I love this idea of volcanoes and the surface of Mars being a little bit more tangible than dark matter. Yeah. Dark matter, really fascinating-- but you can't really interact with it in the same ways that you were describing. Mm-hmm. 

Levben Parsons: Yeah. Yeah, exactly. So you really can only study the impacts it has on the things around it.

Whereas with a volcano, you can go, you can measure the amount of lava that's coming out of a volcano... measure the content of the gases. And there are all of these analogs, there are literal volcanoes on Earth. 

Erin: Yes. 

Levben Parsons: So even though we can't go to Mars, we can study Earth volcanoes and apply that to the Martian system to really get a sense of how volcanoes have shaped Mars's surface and its atmosphere through time.

Erin: Excellent. Trying to draw volcanoes...

Levben Parsons: Of course--, like volcanoes are just like really cool. 

Erin: Oh, yeah.

Levben Parsons: I like, never thought that I'd get into volcanoes and volcanology because I thought, quite frankly, it was just like too cool for me. And I thought people who studied volcanoes were like-- I don't know-- this like rarefied group of people who just seem so cool.

Like you go to active volcanoes and study them? And I, I just, it felt unrealistic for me.

Erin: Let's jump into our first question about the paper.

So like, as an outside reader, I was curious what sort of impact the research itself brought to the broader conversation about the Martian sulfur cycle. So yeah-- in your opinion, like what does the study offer our broader understanding of sulfur on Mars?

Levben Parsons: Yeah. So I think the, the biggest impact of this paper is the fact that it adds a, I think, a new dimension to our understanding-- actually, two new dimensions to our understanding of sulfur on Mars. So previous work really focused on snapshots in Mars's history.

That's primarily because previous studies have relied on things like meteorites that come from Mars, and it turns out that the majority of meteorites that come from Mars are incredibly young. So they can tell us a lot about what's happening in Mars's recent history, but not necessarily what was happening in Mars's ancient past.

Erin: Mm-hmm. 

Levben Parsons: So this project really allows us, for the first time, tell a chronological story of what was happening, or what-- Yeah! What was happening. With the sulfur cycle on Mars through time. So, from like 4.2 billion years ago to say 200 million years ago. So we're able to tell that chronological story, which has never been done before.

Yeah, and it's quite exciting because like the concept of a cycle sort of implies that there is a time component and you can't really talk about cycles if you can't say how much sulfur existed a billion years ago, 2 billion years ago, 3 billion years ago. So I think that's, that's really important.

Another downfall of meteorites-- and meteorites are great, by the way. If you've never handled a meteorite, you definitely need to do so immediately! They're really cool. But, these meteorites that come from Mars, we know they come from Mars, but we don't know exactly where on Mars they come from. So they don't have that geologic context, which is incredibly important for telling this story.

So in this work, we've used regional data in a fairly novel way. So we can say, 'okay, here, in this particular region of Mars, here is what we think the content of sulfur would've been in those magmas. And here is how much sulfur we think would've erupted into Mars's atmosphere from that location'.

So whereas previous studies really just focused on 'what's happening in general', we're... we're telling a regional story, but we're telling a chronological story.

Erin: So I'm drawing meteorites and... I first drew them kind of landing on Mars, but it sounds like these are meteorites that we had access to-- so they landed here on Earth. 

Levben Parsons: They landed on Earth. Exactly. 

Erin: Got it. 

Levben Parsons: So some... something would've hit Mars a while ago and chucked a chunk of Mars's crust out into space. And as you know, space is an incredibly chaotic place.

So some of that stuff made its way to Earth. And, yeah, so we can definitively say these things come from Mars, but we just don't know exactly where on Mars.

Erin: I'm drawing like, mostly like there's some, there's a contrast between like a full length, timeline versus these like little punctuation lines, which are the meteorites. 

Levben Parsons: Exactly. Exactly. And of course we, we use meteorites, we use orbital data, we use rover data as well. So we're using, we're combining all of these forms of information to, to tell that sort of chronological story.

Erin: You kind of answered this already I think you actually answered the second question I was gonna ask about, like, 'what was something that we kind of misunderstood...', and I think one of the core things you spoke to was just like, 'we need to have more of a continuum' and this research that you were doing was kind of creating a more cohesive story. Was there any other misunderstandings that maybe this research like unpacked a little bit more? 

Levben Parsons: No, I think if anything, this work has confirmed some of the things that we generally thought about the Martian mantle and its sulfur content. So I think it compliments a lot of past work quite well.

I think one of the potential misconceptions is the way we use the data. So folks thought that this data couldn't potentially be used in the way we used it, and we're like, 'no, no, no, we can actually do this with this data'. So by sort of leveraging the data in a, a novel way, I think we're addressing some of the misconceptions that folks had about the data itself.

Erin: Did you go and find these meteorites in the field or were these like samples that were available from like other institutions?

Levben Parsons: Yeah, these are samples that were readily available. Like folks go to Antarctica, Africa, they find these meteorites and then they bring them back. So I really just worked with the numbers that came back from them. 

Erin: Oh, okay.

Levben Parsons: That said, I did, look at meteorites under the microscope, but wasn't actually necessary for the work that I, that I do. 

Erin: And when you say you got the numbers, I'm guessing you got like the data itself?

Levben Parsons: So that data is, is published... so, all the meteorite data is published. All of the rover data is published, and it's out there. Anybody can look it up, which is kind of the amazing thing about like American science. NASA just publishes literally everything for the world to use freely and that's kind of incredible. 

Erin: Can you briefly speak to some of the historical hypotheses that people have had about the sulfuric cycles on Mars?

Levben Parsons: Yeah, for sure.

So I think for the most part, people hypothesized that the bulk of sulfur that exists on the surface of Mars at present came from Mars's interior. So it's all volcanogenic sulfur, a sulfur that came out of a volcano. And, there is likely to be some sulfur on the surface that came from, uh, space. So, impacts from meteoroids, asteroids hitting the surface, delivering sulfur and other elements, of course, the surface. But we do think that the majority is from the interior. I think one interesting thing that folks are constantly trying to think about an answer is, is the opposite end of the cycle.

So we're really focusing on sulfur, leaving the interior of the planet. On Earth, I'm sure you're familiar with like 'subduction', and 'plate tectonics'. Well, it turns out that Mars does not have plate tectonics. So on Earth where, you know, the crust is being recycled back into Earth's interior where it can form new magmas.

That process, as far as we know, doesn't exist on Mars.

Erin: Mm-hmm.

Levben Parsons: So it's one of those like big questions about 'what's, what's going on'? Like sulfur makes it way to the surface-- where does it go? And I think that's kind of what we're trying to answer to some degree. 

Erin: Yeah. Was there ever plate tectonics on Mars?

Levben Parsons: In the past. Yeah.

So there's this one idea that... this was 4.2 billion years or so ago... that Mars had a single plate; it's like a 'closed lid' or a 'single lid planet' or something like that. So the idea is that it did have at least one or a few, like ridges.

So not a fully articulated set of plates, like on Earth, but at least like some rifting. 

Erin: Okay. 

Levben Parsons: Evidence for that is pretty, pretty obscured. Based on the fact that it's been billions of years. 

Erin: Oh, fair. It's been obscured. Okay. 'cause at first I was like, 'oh, it's obscure. Okay.' But now it's like, 'it's just been so long'. 

Levben Parsons: Yeah. So it's been weathered away. So evidence of it, it's not readily seen. 

Erin: I might be-- I'm going off script for a little bit just because... plate tectonics? Cool! You said, 'single lid'? 

Levben Parsons: Yeah, I think it's called 'single lid'. 

Erin: Okay. And that's like... 'Mars just had like one big plate'. 

Levben Parsons: Just one plate. Yeah. 

Erin: Versus like Earth has like multiple plates on it. 

Levben Parsons: Yeah, exactly. 

Erin: Cool. I'm gonna try and get that. That's gonna be fun.

Levben Parsons: And I think that's what makes Mars an interesting planet because... you're familiar with the ring of fire? Yeah. And the majority of Earth volcanoes are found at the intersection of plates. But-- if Mars doesn't have plates that are intersecting with each other, a big question is like, how can it have volcanoes to begin with? Right? 

Erin: Yeah. 

There is no ring of fire on Mars, but there are certainly volcanoes on Mars.

All the volcanoes are ancient, by the way. They're all extinct. As far as we know. But they are all hotspot volcanoes. So Hawaii is a great sort of analogue where you have a plate, a volcano that's in the middle of a plate. So we think all of these volcanoes are hotspot volcanoes. So even though it's a single lid planet, it's still very volcanic rich. It has the, I'm sure you know this factoid, Mars has the largest volcano in the entire solar system. Olympus Mons. Olympus Mons! Yes. Yes. So that's one of the, the volcanic provinces, the areas of study in this paper, Olympus Mons. I mean, you can't really talk about volcanoes on Mars without like,

Erin: Yeah. Like 

Levben Parsons: it would be problematic. 

Erin: Yeah. I try to draw like multiple plates on Earth and it definitely looks bizarre. So I'll put that it's an artist's interpretation.

Levben Parsons: Sure. 

Erin: Fantastic. Okay, so prior to reading this paper, I felt like I underappreciated sulfur. Can you tell me a little bit more about why you focused on sulfur?

Levben Parsons: Yeah, so sulfur is definitely underappreciated, and it makes sense. Especially, in the context of volcanoes because when volcanoes erupt, they emit gases, as you know, and we really focus a lot of the time on the carbon dioxide, because that's the thing that I think has a lot of, of very visible impact.

We know the effect that carbon dioxide has on Earth's climate, but volcanoes emit a whole bunch of other gases too including like water vapor... but sulfur and, a lot of these massive volcanoes on Earth like El Chichón or Mount Pinatubo that's in the Philippines, 1991, it erupted one of the largest eruptions of the 20th century.

It produced so much sulfur that it actually led to the global average temperatures dropping by one to like two degrees Celsius, which is kind of insane. So if you could have just like sulfur impacting Earth's climate, it's a major driver. It's something that we need to consider when we think about Mars and Mars's past climate.

So sulfur on Earth can lead to lower temperatures, but in the right context it can actually lead to warmer temperatures. It can act as a greenhouse gas. So it's very context dependent what impact sulfur will have on climate. So, bringing it back to Mars, one of the biggest debate wars you can, you can call it, that scientists have is whether or not like Mars in its past was warm and wet, or cold and dry.

That's like a big debate. And it's, it's like ongoing.

Of course I think the answer is somewhere in the middle. Like there are probably periods where it was warm and wet, and periods where it's cold and dry. But what we know about Mars's atmosphere today allows us to sort of build a picture of what Mars's atmosphere was like in the past, and it would've likely have been composed of carbon dioxide as it is today, primarily. It would've been thicker in the past... even with all of the, that increased amount of carbon dioxide temperatures would never reach high enough for liquid water to actually exist on the surface. So, climate modelers try to make sense of like all of the geologic, morphological sort of physical evidence for liquid water on the surface.

Like in the talk, I must have showed pictures of like, river valleys and uh, like river deltas, like these are things that you can actually see. So how do you reconcile this like physical evidence with these climate models that show that it's impossible to form liquid water on the surface? So what they do is they add other greenhouse gases.

You add water vapor alone and it's not enough to get temperatures high, but as soon as you begin adding sulfur, that's where you can get temperatures approaching that magic number where liquid water can actually persist. It has to be a lot of sulfur, in high concentrations. So this work is important because, I think, we don't know what those numbers are. So, we need to figure out how much sulfur was actually emitted to Mars's atmosphere and over what period of time that sulfur was emitted to get a sense of whether or not sulfur is the missing piece that could actually lead to temperatures on Mars being warm enough for liquid water to exist.

So that's kind of like the reason why we care about sulfur. Another really important thing is like the sulfur cycle on Mars is like the carbon cycle on Earth. So the carbon cycle on Earth is really important. It like drives our climate, like it drives the surface chemistry of our planet.

The carbon cycle is like the most important geologic cycle on Earth. But on Mars, it's sulfur. Like Mars is sulfur rich, like rich, rich. So it's like an order of magnitude more sulfur rich than Earth's surface. 

So, that was one of the biggest surprises when-- I forgot what mission it was, but one of the very first missions that landed on Mars, probably like Pathfinder, Viking... it realized just how sulfur rich Mars was.

And that's kind of like tied with how iron rich it is. It turns out iron loves sulfur and sulfur loves iron. So where you find a lot of iron, you find a lot of sulfur. So because Mars is also iron rich, it's sulfur rich or vice versa. So it's, it's really, really important.

Erin: Uh, this is a really basic question, but we have like a sulfur cycle as well? 

Levben Parsons: Mm-hmm. 

Erin: So the carbon cycle is much more, I guess, 

Levben Parsons: Yeah. It's much more robust. There's a, a lot less sulfur on Earth. So, the impact would not be that great.

Erin: Could we go back to-- you were talking about the war with scientists.

One being like, there's a group of people who might believe that the surface of Mars was once warm and wet versus…what was the opposite one? 

Levben Parsons: Cold and dry.

Erin: Got it. 

Levben Parsons: And at the sort of crux of this is what we call the faint young sun paradox.

Erin: Ooh. Oh, is it because the sun was literally younger when this was happening?

Levben Parsons: It, the sun was younger, but also a lot dimmer. 

Erin: Oh. 

Levben Parsons: In the beginning of the solar system, the sun was a lot dimmer. Over time, the sun brightness has increased and it will increase. So billions of years ago, Mars didn't receive a whole lot of sunlight.

So if it didn't have a lot of sunlight-- like, how are we able to produce a warm and wet environment?

Erin: Yeah. 

Levben Parsons: So that's where the atmosphere like comes into play. 

Erin: Uh, is this controversial to ask, but which side of the war are you on? 

Levben Parsons: I feel like, like in my heart of hearts, I'm on the like warm and wet side of things. And I think as I sort of mentioned before, I think the answer is somewhere in the middle. So intermittent periods of, of warm and wet, interspersed renewal; long periods of cold and dry, interspersed with periods of warm and wet. Like if you have like runaway greenhouse effect or something, or if you have a lot of sulfur being emitted into the atmosphere, that can make it warm and wet.

Erin: Yeah. This is fantastic. Yeah, I now appreciate a lot more and I, I'm definitely trying to capture a little bit how there's more of an abundance on Mars.

I think that was another thing that I was kind of missing a little bit: sulfur cycle is pretty integral to that environment, which makes it really hard now, for me at least, to make these comparisons of what the environment looked like on Mars versus Earth. I don't know what a sulfur rich environment would look like.

I wanna better understand the segment of the paper that was focused on geological context. Can you walk me through at a high level of how you generated the geological context and, and maybe why as well? 

Levben Parsons: So geologic context is, in context in general, is like really important.

With the type of model that we used, it's highly, context dependent and requires a very specific kind of, of rock basalts, which is a volcanic rock. So we had to be very deliberate in where we used or where we got our data from.

Erin: Okay. 

Levben Parsons: There are people who have spent a lot of time studying Mars maps and building Mars maps and classifying all the different regions of Mars.

So it was a true deep dive into, into the literature to get a sense of what are some of the best places that meet that criteria, i.e. where are the places where we expect that the region is primarily made of basalts? Which is the most abundant volcanic rock probably in, in the entire solar system. It's the most abundant rock in like Earth's crust. And it's like, it covers the moon; like, all the dark regions on the moon-- that's basalt. 

Erin: Oh, what? 

Levben Parsons: Yeah, it's like flood basalt. So like you had some volcano just flooded these like massive craters. Um, and that's the same for, for Mars. It's, it's surfaces covered in, in basalt, but some of that basalt is obscured by dust.

So we wanted to find areas, regions... volcanic provinces, we call them... that are not just basalts, but also aren't obscured by dust, because we don't care about the dust, we care about the rock.

Erin: When you say not obscured by dust, were you like looking at orbital data or something? 

Levben Parsons: Yes. 

Yeah, exactly.

So the orbital data... it's just measuring what it sees and it goes down a meter or so. But if that meter is just dust, then that doesn't tell us what the rock is made of.

Erin: Gotcha. I probably can google this, but why is basalt everywhere?

Levben Parsons: Oh, yeah. So basalt is-- 

Erin: We're here, we're talking about it. 

Levben Parsons: It's, it's what comes out of volcanoes. Okay. So, yeah, so like Hawaii, that's all like flood, that's basalts. Iceland is all basalts. The bottom of the ocean is basalts. So volcanoes, especially those that do not erupt explosively and those that just ooze out lava. They just ooze out lava that cools and it cools into generally basalts.

Erin: Okay. Yep. So in, in pieces, I kind of understood what volcanic provinces were. 

Levben Parsons: Mm-hmm. 

Erin: Counting and Martian timelines. But I'd love to hear more of like your kind of description of these three elements that kind of made up the context.

Levben Parsons: So the volcanic provinces, these are regions on Mars that have physical evidence of volcanic activity. So that could be simply a dome, like a shield volcano, like the ones we find in Hawaii. Those are examples of shield volcanoes. So you literally can see it. Olympus Mons for example, or the Tharsis Montes, those are the three like triplet volcanoes you can call them, that are in a line just off to the side of Olympus Mons.

So pretty much any area that had pretty irrefutable evidence that it was volcanic in, in origin. We call those volcanic provinces and these were the regions we were interested in.

Crater counting is actually really cool. It's the way we figure out the age of these volcanic provinces and that's where we get that chronological story from: we need the ages. Now typically to age a rock, we take it into the lab and do radiometric dating or something to figure out very precisely how old that rock is. But we can't do that with these regions on Mars. We can do it with meteorites, but we don't know where those meteorites come from.

So we have to use crater counting and crater counting is like low key one of the most brilliant things ever. It's really simple. Literally you have two regions of Mars.

One region has a lot of craters. The other region doesn't have a lot of craters. Which of those two regions is older? It's a comparison.

The one with a lot of craters is older because it's been around longer. So it's been exposed to impacts from space. So if you see a region on Mars that has little to no craters, you know that it must have formed fairly recently. So maybe a volcano erupted and covered the surface, smoothing it out.

If there are no craters whatsoever-- give it a billion years and there will be craters. So it's just a nifty way to age or date a a region. So crater counting adds that chronological piece that was missing. So we have all these volcanic provinces. I think there were 12 we used. And we had ages for all of these 12 volcanic provinces and they span Mars's history and build that timeline.

So I think you also asked about the timeline too. There are these like three general time periods in Mars's history. You know, there's geologic time on Earth, there's like the Jurassic and there's the Triassic. On Mars, there are three major eons. One is the Noachian..

Erin: Noachian, that's how you pronounce it.

Gotcha. 

Levben Parsons: Then you have the Hesperian, and the last one is the Amazonian, which lasted like 3 billion years. So in some, that's like 4.6 or 5 billion years, the age of the solar system.

Erin: That's helpful.

You use gamma ray spectroscopy from Mars Odyssey to estimate sulfur concentrations. 

Levben Parsons: Mm-hmm. 

Erin: Why Odyssey? I assumed it was just instrumentation, but...

Levben Parsons: So, Mars Odyssey, it had that instrument on it, the gamma ray spectrometer. And what it allows you to do is measure the chemistry of the surface rocks. So, it measures things like sulfur. It measures like how much iron there is in the rock, like the concentration of iron, oxygen, silicon, all of these elements.

And that's really what I needed for the mathematical model that I used. I needed the actual chemistry.

With Mars Odyssey, we can get sort of like the whole surface-- not the whole surface! It's really limited to the mid-latitudes, so it doesn't quite get to the poles because the poles have a lot of ice and water-- H2O, which mess up the instruments. So it's not able to accurately get a sense of the chemistry of the rocks.

If there was a lot of like H2O. 

Erin: Interesting. Okay. That, that's actually kind of harder to depict a little bit. But I did get the the idea what you were looking for was more of the chemistry. Is a Rover two, which rover? 

Levben Parsons: Great question. I have to say it's Spirit. Oh.

Because I just, I, I think I, I just used the data and I'm pretty sure it's Spirit because it was, it's from Gusev and I, I think Spirit was the one that went to Gusev crater. 

Erin: Okay, cool.

Levben Parsons: It's one of the early, I guess not one of the OG rovers, but that's like one of the rovers when I was like in college that was roving around.

Erin: So given the sulfur enrichment index, and from what I gathered from reading the paper, um, it seemed like you were trying to establish a way to compare how much sulfur we see at the surface today to what was likely present in the original magmas.

Levben Parsons: Yeah. 

Erin: So it's kinda like this benchmark was the SEI missing from past studies. 

Levben Parsons: Yeah. So your characterization of SEI, first of all, is like exactly on point . And it wasn't something that had been done before. I think primarily because no other studies had a regional sense of what was going on.

We had all of these 12 volcanic provinces across the surface of Mars; so, we could do something like this. Whereas in the past, it was more of like a general sense. I think it's really important because it, like you said, it is a benchmark and it allows you to get a sense of how sulfur is mobilizing or moving on the surface of, of Mars.

So sulfur is what we call a volatile, which is a lot like carbon dioxide or water vapor. When it's in a magma deep inside the Earth, the analogy that everybody uses like a soda can. Obviously, it's under a lot of pressure, so that carbon dioxide is like in its liquid form, but as soon as that magma begins to rise, that pressure decreases.

You pop the can of your soda and all the sulfur or carbon dioxide comes out as bubbles. 

Erin: Oh, okay. 

Levben Parsons: So the sulfur that's in these magmas, deep in the interior of Mars, begins to get closer and closer to the surface, that sulfur bubbles out. And it enters the atmosphere. So the lava that forms on the surface, it doesn't record how much sulfur the magmas originally had-- because it lost all of its sulfur. It's this volatile that just escaped into the atmosphere. So even though like Mars Odyssey can measure the amount of sulfur on the surface, that doesn't tell you what was going on in the interior. It just tells you how much sulfur was on the surface.

So the SEI is a way for us to track the concentration of sulfur in that region versus how much there is today. And that just gives us a sense of where sulfur is mostly enriched and where it's slightly depleted.

The moral of the story is if it was a one-to-one ratio, that would mean that sulfur didn't go anywhere. But the fact that it's not a one-to-one ratio tells us that sulfur is going places.

So if you think back to like those big volcanoes that I mentioned earlier, like Mount Pinatubo or like El Chichón [in Mexico], like when they erupted that like ash plume went high up into the stratosphere and it orbited Earth in a few days.

Erin: Wow. 

Levben Parsons: So it was able to come back to like, you know, make a full orbit in a few days. So whatever sulfur is being erupted by these volcanoes, it's like far flung from where it came from. So it's really difficult to sort of trace where it's actually going, but we're trying to get a sense of okay, 'where is it likely going'?

And what's, what's cool about the SEI is that there's a map in the paper where we show the SEI for each of the provinces. What we see is that sulfur is more enriched in the southern hemisphere of Mars, generally speaking, than in the northern part of Mars. So the southern highlands versus the northern lowlands.

And uh, the reason we think is it's actually quite simple. It just has to do with age. So generally speaking, the older the volcanic province, the more sulfur is there. The longer it's been, it's been on the surface, the more and more sulfur can accumulate in that spot. 'cause these volcanoes would've been erupting throughout Mars's entire history.

So if you have a really old area, then it can just, like all of that sulfur can accumulate on the surface. So it's a very simple explanation. 

Erin: Okay. I've got some, a couple of like yeah. Drawing diagrams going on here. So taking a step back, you said that the south was more 

Levben Parsons: Yeah-- so south is more enriched.

Erin: Okay. So there's more sulfur like on the, the ground. 

Levben Parsons: Yeah. Enriched compared to how much there should be. 

Erin: Okay. 

Levben Parsons:  And we called it the southern highlands because it's high, it's like very mountainous. So the southern highlands of Mars is more sulfur enriched compared to the northern lowlands. So if there were ever an ocean on Mars, it would primarily be in the northern hemisphere of Mars, just because it's lower.

Erin: Yeah. Oh my God. I don't know how to draw an ocean for this, but we're, uh, yeah, we'll just like, we'll just make it look like there's an ocean here. 

Levben Parsons: I mean, you can use red for the ocean because there's this concept of like, uh, magma ocean. So early in the formation of like, these planets, you know, it's just like all magma... 

The paper that we're talking about is after a magma ocean for sure.

So it's not, not really relevant. 

Erin: It's just objectively cool. So I got distracted. 

Levben Parsons: Yeah. I mean like, who doesn't like magma oceans? 

Erin: So back to the diagram. So I do have like the southern highlands more sulfur enriched.

You had mentioned that once it starts to like reach the surface, the sulfur is kind of like up at the top closest about to kind of just burst 

Levben Parsons: It's bubbling out. Yeah. 

Erin: Bubbling out. And so, can you tie that really quickly back to the SEI yeah. 

Levben Parsons: Yeah. So the SEI, it's a measure of how much sulfur is in the magmas relative to how much sulfur is measured on the surface today. There we go. 

Erin: Okay. 

Levben Parsons: Yeah. So the sulfur that we measure on the surface does not directly reflect how much sulfur was in the magmas.

Erin: Yep. Okay. 

Levben Parsons: And the SEI helps us just get a sense of how different those two are, how much sulfur is on the surface versus how much sulfur was in the magmas at that location. 

Erin: Okay. There we go. I'm gonna have you look at that part at the end of this to see if I got the relationship right. But this works. That's the, 

Levben Parsons: It's really tricky. It's really tricky. When I first started like this entire endeavor, it was one of the things that I couldn't quite make sense in my head. 

Erin: Hmm. 

Levben Parsons: Just like-- how mobile sulfur is. 

Erin: Yeah. 

Levben Parsons: It's like we're measuring sulfur on the surface. So why do we care about how much sulfur was in the magmas? Like why does that matter?

Turns out it matters a lot. 

Erin: There's a delta, I guess. 

Levben Parsons: Yes, exactly. 

Because that tells us how much sulfur was actually emitted to the atmosphere. And that's what we need to know how much sulfur is emitted to the atmosphere, because that gives us the, the pieces of the puzzle to figure out whether Mars is warm or wet.

Erin: Or somewhere in between. I also like that theory. 

Levben Parsons: Yeah. 

Erin: Can you speak to the specifics of the impact, itself of the SEI? How does this index help us better understand Mars's uh, sulfur cycle overall? 

Levben Parsons: Mm-hmm. 

I think it just gives us a frame of reference and allows us to just get a sense of where sulfur is going. So one of the things that I tried to do originally in the paper that didn't quite pan out was look to see if the content of sulfur close to the volcanoes was a lot higher than farther away from the volcanoes.

And I didn't really see a relationship like that.

But that's something that you can work through with the SEI because it's like a color map, where you can see gradients of color. And by seeing these gradients you can see what the trend is, like where it's moving.

Is it moving northerly or is it moving more southerly, or what sort of just general patterns there are when you can see that gradient map on an actual map. Utility is really in just visualizing the state of sulfur on Mars. 

Erin: Okay. Love that. Could this metric be repurposed in future studies? Uh, and if so, in what ways? 

Levben Parsons: I will say that, that last question was really hard to answer. 

Erin: We can skip it too! 

Levben Parsons: No, but I'm, I'm glad you asked because I feel like it's really important. 

Erin: Yeah! 

Levben Parsons: And uh, I feel like it's really difficult to, to like explain.

I think if in future studies folks apply the Mars Odyssey data in the way that we did, you can build that like chronological story, not just for sulfur, but for like, you know, maybe water and, and carbon dioxide. So you can easily develop a, instead of an SEI, sulfur enrichment index, but you can develop a water enrichment index, right? And see if, see how water is moving on the surface of Mars.

There are all of these maps that have been published of the river/gully system on Mars. So these are the waterways that have been curved or carved into the surface of Mars.

And we wanted to see if there was any sort of correlation between like the SEI and the locations of these gullies. Like is there more enrichment downriver versus upriver? And that didn't quite pan out in the way we expected. I don't think we actually explored it fully, but you definitely can use SEI think those other ways. 

Erin: For other studies people have been making of life cycles... 

Levben Parsons: Yeah! Yeah, exactly. So water definitely would be a great one to look at.

Early in this work we were looking at potassium actually. So K... because K, potassium, is one of those mobile elements as well. So it's like sulfur in that it's highly mobile and can move around, and we actually have potassium data for the surface of Mars from Mars Odyssey.

I like even mapped it to see what those gradients would look like. Maybe these potassium gradients track the gullies on Mars, but that also didn't quite pan out the way we expected, so we didn't pursue it further. But there are a lot of interesting things and I tried it for like maybe a week.

Erin: And like, can you just like briefly describe a gully?

Like in my head it's like a marsh kind of area, but I don't know...

Levben Parsons: Oh yeah, it's like a... like a small river. 

Erin: Okay. 

Levben Parsons: A small river that has carved out the surface. So they'll have, kind of like these curvy dendritic shapes people call it oftentimes. If you see a aerial of the Grand Canyon, it's sort of like has these like little branches that sort of swivel out.

That's what the Martian gullies look like. 

Erin: Ooh, okay. 

Levben Parsons: They're a lot.

Erin: I never even thought about potassium as being mobile. That's probably also because I'm not in this field, but I like that it's just like a way to kind of conceptualize it.

So ultimately our paper revealed the potential of a much more diverse sulfur generational cycle on Mars. Based on your knowledge as a planetary scientist can you speak to what other processes were possibly at play that generated sulfur on the surface of Mars?

Levben Parsons: So definitely I think volcanic sources would be the largest contributor to sulfur from the surface. But once sulfur is on the surface, there are a whole bunch of other processes at play that will change and move sulfur. So volcanoes-- yeah, it'll produce sulfur on the surface, but there are all these other things on the surface that will actually cycle sulfur.

So if there was a lot of water and if that water was flowing, you would expect to, to form, absorb, or move sulfur around. Especially if sulfur is not quite consolidated, it'll move fairly readily. In fact, looking at the surface of Mars using other missions, we see that there are a lot of these sulfates, which are minerals that form through aqueous processes. Literally, they just form through like water mediated processes. So like water had some dissolved sulfur in it, the water evaporated and left behind salts, for example. So instead of like sodium chloride, it would leave behind a salty 'sulfur-y salt'. So we have a lot of these sulfur sulfate minerals on the surface that can only be formed through liquid water interactions.

So another great evidence for there being water on the surface of Mars. Yeah. Just the very existence of this. 

So that's like probably I would say the biggest contributor to motion of, of sulfur on the surface of Mars. With that said, there are other processes like wind.

Yeah. I love your like hula, like hands for wind. Yeah. It's a great way of, of moving sulfur from like a volcano to the literal other side of the planet. 

Erin: Yeah. 

Levben Parsons: So if you're, if you're talking about like large scale motion of sulfur, wind is gonna do it. Those are the two primary ways, water and wind. And then of course you'll have some like slight burial of sulfur as more material sort of builds on top. You can have that sulfur being slowly buried and buried over time, just like how a sedimentary rock is made. 

Erin: Okay.

Levben Parsons: But I think some of that sulfur, I, I think I alluded to this earlier, is lost to space because Mars didn't have that big of an atmosphere. It didn't have a strong magnetic field that could protect it from solar winds. So a lot of its atmosphere was stripped. A lot of that sulfur is likely to have been just lost to space.

So a lot of it came from space, but a lot of it was then just lost back to space.

Erin: I don't think I fully appreciated that either: there was such a thin atmosphere, you would just lose sulfur to space. 

Levben Parsons: Yeah. You lose sulfur. It's not just the thin atmosphere, but the fact that Mars is just like small. The gravity is just like, I think it's a third of the gravity on Earth, so it can't hold onto its atmosphere as, as effectively as Earth does.

And that's precisely why the volcanoes on Mars are so fucking tall, because it can just grow and grow and grow. There's nothing to stop it from like growing that tall because gravity is just not that strong. Olympus Mons is three times the size of Mount Everest. So you can do that when you have such a low gravity environment.

But that also means that you lose material to space because of that limited or lower gravity. I don't want it to sound like there is no gravity on Mars. 

Erin: Losing precious elements to the space that can happen. 

Levben Parsons: Yeah. 

Erin: Favorite question. So were there any unexpected findings that you observed when conducting this research?

Levben Parsons: I think just some of the numbers were kind of shocking to me. Not just the numbers, but like, because the numbers don't, at the end of the day, mean a whole lot unless you can contextualize it. Like we say that 68 times 10 of the 19 grams of sulfur was emitted to Mars's atmosphere, like throughout its history.

But like, what does that actually mean? Yeah. 

Erin: What's that relevant to? Yeah. 

Levben Parsons: So I was thinking about like, oh, what, what is a, a good thing that people can sort of like relate it to? And I was like, oh, the Grand Canyon. 

Erin: Yeah. 

Levben Parsons: So if you think about all of that sulfur... it would fill 34 Grand Canyons.

Yeah. So I feel like people have a sense of like how vast the Grand Canyon is... so if you're filling that like 34 times, that's kind of impressive. So that's definitely one of those surprising things.

Another surprising thing, and this goes back to when we were talking about the timeline, I mentioned like the Noachian, which was 

Erin: Yeah. 

Levben Parsons: ...a billion years.

The Hesperian, which was like 200 million years, or the Amazonian, which is 3 billion years. What we found was that during the Amazonian and during the Hesperian periods or eons, use a technical term... about the same amount of sulfur was actually emitted to Mars's atmosphere. So during a 200 million time period and a 3 billion time period, around the same amount of sulfur was actually emitted to Mars's atmosphere.

And that has like some really huge implications. 

Erin: Wow. 

Levben Parsons: So if we're thinking about the impact that sulfur could potentially have on climate, if that sulfur was released over a long period of time, then the impacts would be muted. It wouldn't be as pronounced. But if we're releasing all of that sulfur over a fairly short period of time then the impacts are exaggerated.

So I think that's really the kind of like the hidden gem of this paper that wasn't really like highlighted. We're able to say, or we presented like a sulfur flux. 

Erin: Yeah. 

Levben Parsons: You don't really appreciate it unless you explicitly say, 'over 200 million years, the same of sulfur was released as over 3 billion years'.

And, if we're talking about getting the content of sulfur into the atmosphere to be great enough for liquid water to exist, for the temperatures to be warm enough for liquid waters to exist... then you need to pump a lot of sulfur in over a short period of time. 

Erin: Which is what happened in the Hesperian?

Levben Parsons: Exactly. Exactly. So that's why I think Mars had intermittent periods of like warm and wet and. 

Erin: I'm sorry, I keep interrupting you... I never do this, but now I'm just like, it's all clicking where It sounds like if there was like this warm, wet period, it would be in the Hesperian timeframe? 

Levben Parsons: Probably! Yeah. Yeah. 

I think there's a lot more work to be done trying to link those two things: this like massive outflux of, of sulfur and maybe some of those physical artifacts of flowing water. 

Erin: Given what you learned from this research, do you personally have remaining questions that you'd like to further explore?

Levben Parsons: Oh yeah, for sure. And I think it goes back to what I think is one of the bigger implications of this paper, i.e. during the Hesperian, you released so much sulfur, but 200 million years is a long period of time, right? So it would be great if we can improve the resolution of this, this work. So I really think this is kind of the beginning. Prior, it was literally just a snapshot, and now we have like sort of a timeline, but the timeline is still pretty low resolution.

So we really need to know what Mars's volcanoes were like in terms of did they erupt fairly quickly, or were they like these prolonged eruptions? So, if all of that sulfur was released over the entirety of 200 million years, that means something different than if it were released over say, tens of thousands of years.

And I think that wouldn't be completely absurd because there are a lot of analogues of similar situations on Earth where we have similar scales of volcanic eruptions, erupting over really short periods of time, less than a million years, and causing mass extinctions on Earth. 

Erin: Yeah. 

Levben Parsons: So what I think is really cool is it kind of requires you to reframe the way we think about mass extinctions, and volcanoes like on Earth. We think of volcanoes as these life ending events. But on Mars, it could be like the opposite. You have this catastrophic event that pumps so much sulfur and carbon dioxide into the atmosphere that it can actually lead to the conditions necessary for life to form.

So it's like a complete switch.

So that's something I would like to explore some more, just like trying to quantify just how long these volcanic eruptions were likely to have lasted. So instead of 200 million years, what if I can say that all that sulfur is pumped out in a million years? That would be insane. 

Erin: That would be insane-- kind of a busy million years on Mars.

Levben Parsons: It would be. But like I said, there's precedence on, on Earth that has happened and has led to major shifts in Earth's climate. So why couldn't it happen on Mars?

Erin: Yeah. Last question.

If someone from the outside wanted to understand why this work matters, like maybe for those who don't have as much of a background in planetary science, chemistry, or climate or environmental systems, in general. 

Levben Parsons: Yeah.

Erin: What would you want them to take away from the work? 

Levben Parsons: Okay. I immediately think potential terraforming of Mars or occupying Mars... I feel like that's probably a lot more relevant to a lot of people... and that's not what I was planning to say. But I think understanding the history of Mars's climate and the role sulfur played in shaping Mars's climate can help inform how we could potentially make Mars habitable if that were something we tried to do.

So if we learn in fact that 'sulfur is the thing added to Mars's atmosphere, makes temperatures warm enough', maybe we can do some sort of like geoengineering, like, yeah.

As a lay person who, like, why would they care about any of this? I think there's a lot of research actually into using sulfur materials to build habitats on Mars. So there are, I think, a lot of practical applications to studying the sulfur cycle on Mars in terms of like potential geoengineering, but also in terms of like building materials.

But the scientist's answer is, there are some big questions about what Mars's past was like, whether it was habitable, what habitability looked like, how long it was habitable, and whether life was able to form during those periods of habitability. And I think sulfur is like intricately tied to the story of habitability of Mars.

Yeah. So I really would hope folks would sort of take away just how important sulfur is to the climate of Mars and to the habitability of Mars. 

Erin: That's fantastic. Thank you so much. This is this is so good. I really feel like just talking with you, reading the paper itself, it just like really crystallized so much.

So thank you so much for going through it. 

Levben Parsons: You had great questions that I think are very, very impressive questions. I enjoyed reading through them. 

Erin: Yeah. Well you know what? I think that. Um, I haven't done a lot of these visual synthesis yet. But I do think that, for the folks who are able to explain their work really clearly, it's, it's really easy to kind of engage and ask the basic questions and like, open up the curiosity, I guess.

So thank you for being like approachable and Yeah. Just all you've done. This was fun.

Levben Parsons: A lot of fun.