Kyle Kellams: This is Ozarks at Large. I'm Kyle Kellams. Hollywood, H. G. Wells, Orson Welles have all wondered about life on Mars. We're slowly finding more evidence that necessary elements for life have existed on the planet.
Cory Hughes, who just defended his dissertation this week at the University of Arkansas, has been conducting research into whether Mars once had a massive ocean on its northern hemisphere. Previous research has all but confirmed the existence of rivers on Mars in the distant past. Hughes says that's an important building block for his work.
Hughes: The existence of rivers tells us that there was water, liquid water, sufficient volumes of liquid water to create, construct, erode large valleys, construct large deposits. And it was precipitating, right? It was snowing or raining. So there's a full-on hydrological cycle here. And that's very interesting. As far as we understand it, in our universe, all life relies on water to exist. So that's the first thing.
And then secondarily, rivers don't necessarily impute an ocean. An ocean is a massive body of water. On Earth, the rim of the ocean is a very habitable place, right? The place where the land meets the ocean is where we get deltas, for example, which are incredibly biodiverse regions on planet Earth. A lot of humans live there, too. But rivers on their own don't point to an ocean, but they certainly tell us there was a lot of water.
Kellams: Depending on orbits — I mean, I think Mars is anywhere between 34 and 250 million miles away.
Hughes: That sounds about right. I don't know the exact number, but that's order of magnitude. That's right. Long ways away.
Kellams: And if we're talking about oceans on Mars, they were probably billions of years ago.
Hughes: Yeah. I think the easy number to throw out there is 4 billion years. Four and 3.7, maybe 3.5 billion years ago, is when we think the ocean was maybe there.
Kellams: So to laypeople, if we're talking hundreds of millions of miles away or billions of years ago, how can we know more about whether an ocean existed?
Hughes: Well, we certainly have evidence of rivers. And those rivers have to go somewhere, right? Rivers carry sediment with them. And when rivers run into standing bodies of water, like a lake or a sea or an ocean, they fan out and create these river deltas that I was just mentioning. Deltas are constructive environments — they're deposits. A river valley, that's an erosional environment. It leaves a scar on the surface. But at the other end of a river system, after it's done eroding, it deposits this big fan-shaped sedimentary wedge. And that's the delta.
And we see these deltas sort of rimming the northern lowlands. I don't know if you're familiar with this concept of the hemispheric dichotomy on Mars.
Kellams: No, I'm not.
Hughes: So there's sort of two sides to Mars. The southern hemisphere of Mars is very hilly, high elevations or high variability in elevations. The terrain is very old. And then the northern hemisphere of Mars is like one big basin, maybe an ocean basin. So that's really the punchline of this paper — that we find these wedge-shaped deposits, these things that look like river delta deposits, on the rim of this giant hemispheric basin. So there's this pretty strong history of evidence that points to this northern hemispheric basin being one giant ocean.
Kellams: And this may be obvious, but we know about this basin because of satellite imagery.
Kellams: Yeah. It's very clear.
Kellams: Which means that satellites haven't been around, geologically speaking, that long.
Kellams: Yeah. So this is relatively newer information. Certainly in the broad context of human history, it's very recent. Or geologic history.
The first, I think, hints of this northern ocean hypothesis came maybe in the ’80s. The Mariner missions were the first NASA missions that made it to Mars and sent back some really high-quality images. Those were in the early ’70s, and that was when we first saw these big erosional scars. We saw there was evidence of flowing water. And I think it probably took another five, 10 years before we really had a good look at the broader geologic or topographic features of the whole planet.
And there was a guy named Parker — Gary Parker, I think was his name. He was the first one to point — it might have been 1979, actually — he points to this northern hemispheric basin and he's like, I think there might be an ocean here, or an ocean basin.
Kellams: So we have rivers and sediment and deltas on Earth. Can we use information we have on Earth to project about what we might know about Mars?
Hughes: That is the essence of my dissertation. Yeah, that's why I came to Arkansas. My background is primarily — I'm a geologist, and my focus in my undergrad and my master's was studying Mars and studying river delta deposits on Mars specifically. And I came to Arkansas to study with a guy, John Shaw, who was not a Martian geologist. He was an Earth delta expert. So I wanted to learn everything I could about Earth's deltas so that I could better inform my research on Martian deltas.
Kellams: So when you come here and you start this academic relationship with John Shaw, what do you tell him?
Hughes: That was pretty much my application essay. That was it. And he was on board.
Kellams: Could you use northwest Arkansas as that study?
Hughes: Great question. Very coincidentally — surreptitiously, you might say — there are some rocks in northwest Arkansas, the Wedington Sandstone, we call it. They're actually just 30 minutes away from where we're sitting right now. They are an ancient river delta deposit from 300 million years ago, the Mississippian age. And they bear a striking resemblance to the deposits on Mars. They're preserved in inverted relief, we call it — they poke up out of the ground in a very specific way that is very similar to how deltas on Mars look.
So we get a chance to essentially walk around the surface of Mars in a figurative sense — literally in some ways. And yeah, that was a real lucky set of circumstances. I didn't know that was here when I applied. And so that's been a real boon to my research.
Kellams: So it's called Wedington Sandstone. Is it out near Lake Wedington?
Hughes: I would say the type locality, yeah. It's kind of all over northwest Arkansas, a little bit in Missouri and some in Oklahoma. But it stretches from Pea Ridge to Wedington, Elkins. It's kind of all over northwest Arkansas.
Kellams: And is this unique to northwest Arkansas?
Hughes: The Wedington Sandstone? Yes. Delta deposits preserved in the rock record? No. But the topographic inversion, the inverted relief — that is unique to northwest Arkansas.
And to give you a bit more detail on what that means: think of a river. A river is a negative relief feature — it's a channel. And at the base of this channel, moving water is carrying sand grains or gravel grains along the base of the channel. Over time, the coarse grains in the base of the channel are preferentially deposited there. And finer grains like mud, very small particles, are deposited in the overbank and the floodplain.
If you take the water away from this system, it dries up over many millions of years. Then we bury it very deeply. It turns into rock. That's the process of lithification — this is how we get sandstone from sand. We bury it very deeply, it heats up, everything kind of welds together. And then through processes of erosion, we lower the surface back down. The negative relief feature that was the river is now a bump.
So the river channels of the Wedington Sandstone are ridgelines. That's what Pea Ridge National Battlefield is. That ridge up there is actually a 300 million-year-old river delta deposit. And that's how they look on Mars — they're all ridgelines out there. So we can study the ridgelines in northwest Arkansas to learn about the ridgelines on Mars, which tells us about the history of the oceans on Mars, which gets at whether or not there was ever life on Mars. So it's pretty fun — it's fascinating.
Kellams: I want to get back to what you just said in a minute about life on Mars. But first, if we're talking the northern hemisphere of Mars, chances are it was a big ocean.
Hughes: Yeah. Very big. It's not quite 50 percent, right? That would be the definition of the northern hemisphere. But it's most of the northern hemisphere.
Kellams: As we know it, if you're going to have life, you’ve got to have water.
Hughes: Right. We haven't seen proof otherwise in the universe.
Kellams: So if there was ever life on Mars, this would help — this being the ocean.
Hughes: The ocean? Yes. I think a very simple argument can be made: more water, higher chance of life.
Kellams: You could live another 70 years.
Hughes: Sure.
Kellams: And we wouldn’t know if there were life on Mars.
Hughes: Yep.
Kellams: Is that okay?
Hughes: Well, I think I would be disappointed, but that is okay. I'm also holding out hope for some other planets in our solar system or planetary bodies — Europa, Titan, some moons of Jupiter and Saturn. Those are very alien worlds, but there's a lot of water on them. And Titan specifically has organic matter all over the surface. That's different than life, but it is the building blocks of life. So I'm optimistic that at some point in my lifetime, we'll find at least microbial life somewhere in our solar system. I'm not certain that it'll be Mars. Certainly a lot of water there. I'm a little skeptical because I'm surprised we haven't found it yet — direct evidence of life. We've been there for a while. We've had a few rovers go out there.
I don't know if you've heard about this new rock from the Perseverance rover — the Bright Angel formation. There was a recent release from the Perseverance rover team. They found some rocks in Jezero Crater where that rover is currently exploring. And there are some chemical signatures — some reduction halos, they call them. And their paper, which I think is published in Science Advances or Nature, one of those big journals — the punchline of it is essentially: we looked at these halos, these chemical signatures in this rock that we took some photos of and sampled with our instruments, and we looked at all of the pathways to get these specific chemical signatures that we know of. And the abiotic pathways don't make sense with the set of circumstances that we're seeing in Jezero Crater and in these rocks. So the biologic pathway, the biotic pathway, is, based on our process of elimination, the most likely.
So I would say the best evidence that we've found that there may be life was recently found in the Bright Angel formation in Jezero Crater by the Perseverance rover team.
Kellams: So maybe we'll see in our lifetime. But the problem is we need to get those rocks back to Earth.
Hughes: To me it's just amazing that we're even talking about that — getting these rocks back to Earth.
Kellams: Do they have a plan for that yet?
Hughes: We do. So the Perseverance rover, which launched in 2020 and landed on Mars in 2021, is the first leg of a sample return mission. Along with its other instruments on board, the rover has instrumentation for sampling the surface. So it drills into the surface at various points in Jezero Crater — which, by the way, has a river delta in it. It was a lake, not part of this ocean complex that my work looks at.
So we're looking at a river delta, we're driving a rover along it, and we poke holes in the delta every once in a while and store some of that rock that we drill out in these metallic tubes. And then the rover drops little caches of these tubes of samples throughout the crater. The idea is that we're going to send another mission out there to retrieve those sample caches and then bring them back to Earth. And there are a few different ways to do that. All of that is in the planning stage, but we've done the first step of it. So we're halfway there, you might think.
Kellams: Do you allow yourself to romanticize at all? If you're at a river delta — say you're at the Mississippi River — do you allow yourself to close your eyes and think, okay, 3.7, 4 billion years ago on Mars, it might have looked something like this?
Hughes: Do I allow myself to romanticize? Absolutely. In fact, that's the essence of my research — imagining what Earth systems can teach us about what was going on billions of years ago on Mars. So I don't just allow myself to romanticize — it's part of my job.
Kellams: Finally, what got you interested in this?
Hughes: I kind of fell backwards into it, frankly speaking. I was sort of a wayward undergrad without much direction, and I had picked geology. I was interested in science generally speaking, but I didn't have much direction. And I had always been interested in space. I grew up, for the most part, in Houston — figuratively in the shadow of the Johnson Space Center there. And I found a professor at the University of Texas, where I was an undergrad, had done a little bit of research on Martian geology. And I just went and knocked on his door and asked him if he had any opportunities. And coincidentally, he had a grad student who was doing some Martian research, and they handed me over some of their data. And it turned into an undergrad research paper that was pretty well received. So I just sort of lucked into it, followed my passion, and it's worked out so far.
Kellams: And your paper can be found in Geophysical Research Letters, the most recent one.
Hughes: Yeah.
Kellams: You keep in contact with John Shaw?
Hughes: I hope so. Yeah, absolutely. We've got some unresolved business.
Kellams: So you’ve got some time to figure it out?
Hughes: That's right.
Kellams: Thank you so much for your time.
Hughes: Thanks for having me.
Kellams: Corey Hughes — and that's now Dr. Corey Hughes — has research published in the journal Geophysical Research Letters. Our conversation took place at the Carver Center for Public Radio this week. This is Ozarks at Large.
Ozarks at Large transcripts are created on a rush deadline. Copy editors utilize AI tools to review work. KUAF does not publish content created by AI. Please reach out to kuafinfo@uark.edu to report an issue. The audio version is the authoritative record of KUAF programming.
