Water on Mars, Part 1

Planetary geology is a fascinating area--particularly when it pertains to the search for extraterrestrial life. I wrote about it once during my brief stint as a student science writer, but it's not an area that I've really covered on my blog. However, a former colleague of mine from Oxford, Bethany Ehlmann, was recently involved with a couple of papers on geological formations left by ancient Martian water, so I thought that this would be a perfect opportunity. Ehlmann is currently a PhD student in the geological sciences at Brown University and part of the CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) team . Before that, she was a Rhodes Scholar at Oxford, where she completed two MSc degrees. She was recently the fourth author on a paper in Nature and just before that the first author on a paper in Nature Geoscience, both on Martian geology (see references below).

I've broken our interview into two parts. In the first part, published here, Ehlmann discusses her two recent papers. In the second part--which is published in a separate post--she discusses water on Mars more generally.

Bethany Ehlmann Nick Anthis: You have been involved with two related papers that were published recently. Let's start with the one that came out first--your first-author publication in Nature Geoscience entitled "Clay minerals in delta deposits and organic preservation potential on Mars." What's this paper all about?

Bethany Ehlmann: This paper focuses in on one unique part of Mars where we see both geomorphological evidence for liquid water--in this case river valleys and a delta--and chemical evidence for water--in this case, clay minerals.

On Mars, these are not usually found in the same places which has been something of a conundrum. We don't necessarily solve that here. Jezero crater is exceptional in that it indicates an area that has been wet for a long period of time--good for habitability.

NA: OK, that's interesting. Does the fact that they're usually not found in the same places cast doubt on how prevalent water once was on the surface of Mars? Because, it's widely accepted surface water was once very prevalent, right?

BE: I don't think it casts doubt on the water story at all. But, it does mean that it is more complex than our terrestrial intuition might first suggest. On Earth, for example, river valleys are full of clay minerals that alter in the watershed [the valleys that feed it].

Here clays aren't necessarily in valleys and old river channels. This might mean some clays formed underground and that river channels weren't around long enough for chemical alteration to occur.

NA: What do you mean by "geomorphological evidence"? Do you mean land formations that looks like former rivers and lakes?

BE: Geomorphological = landforms. Exactly.

Ancient Martian water in the Jezero crater (link)

NA: In the paper you talk about "organic preservation potential". What does that mean? Does this mean you've identified places where you might find life? Fossils? Fossil fuels?

OK, I'm just kidding about that last one.

BE: Haha. Well, clays in basins are great place to search for oil on Earth.

I'm certainly not suggesting anything like that for Mars. But, the type of clays we found, smectites, have a layered structure. The layers tend to trap materials: other ions, water, and organics, should any have been around. Basically, we found evidence for clay rich sediments in a Mars paleolake.

It must have been wet enough for a long time for clays to form in the watershed. Then these were transported and deposited in Jezero lake and buried. Great place to look for preserved microorganisms.

NA: Now you're speaking my language

BE: The new CRISM instrument on MRO [Mars Reconnaissance Orbiter] is the first to find clays in lakes. Only three craters show clear evidence: Holden, Jezero, and Eberswalde. And, Jezero is exceptional in that its watershed--the valleys that feed it--are chock full of clays. So we know exactly where they came from.

NA: Well, since you brought up CRISM there, let's talk a bit about the techniques that you use. I see a lot of acronyms in these two papers (CRISM, CTX, HiRISE, MOLA) related to the techniques (and equipment) you're using. Is this all infrared spectroscopy?

BE: CRISM and OMEGA are our infrared spectrometers that do the mineral identification. OMEGA was sent by ESA [European Space Agency] and first identified clays and sulfates on the surface. NASA's CRISM has followed up with 20x better spatial resolution to map the geology in detail

IR spectroscopy works by imaging the surface in many wavelengths of light (in CRISM's case, 544), then looking for absorptions (distinct bands of low reflectance) that indicate minerals.

NA: To add a little bit more to that, in case the readers don't know, infrared (IR) spectroscopy measures molecular vibrations. You can think of atoms in a chemical bond as two masses attached by a spring that vibrates at a specific frequency, and therefore at a particular energy. If this chemical bond encounters electromagnetic radiation of this particular energy, then the chemical bond will absorb it and transfer it into vibrational motion. Radiation of this energy exists in the infrared portion of the electromagnetic spectrum. Since the atoms and bonds are arranged differently in different materials, these atoms will vibrate differently, giving rise to unique IR spectra.

BE: Exactly!

IR spectra from CRISM (link)

NA: Both of these instruments are on satellites orbiting Mars. Is that correct?

BE: Yes.

NA: What are those other acronyms?

BE: CTX and HiRISE are two high resolution cameras that image the surface at a resolution of 5 m/pixel and 25 cm/pixel, respectively. While they don't tell us composition, they give us a very good picture of the rocks and sediments and the relationships between rocks with different minerals.

MOLA is a laser altimeter that provides the third dimension -- elevation data.

NA: Have you ever gotten to work hands-on with any of these instruments, either seeing them in person or witnessing or participating in the operation of them?

BE: I actually haven't ever seen in person the flight models of OMEGA and CRISM. I've seen some similar spectrometers being prepared for space missions. And, we have a spectrometer in the lab and a portable one for the field that I use all the time.

I do participate in a small way in CRISM operations, helping to target different parts of the planet and to evaluate the calibration. The bulk of the day-to-day is done at Johns Hopkins APL.

NA: Oh, you do research on Earth geology as well? Not just Mars?

BE: Some, although I'm more and more a Martian (geologist) these days.

NA: Haha. Well, you still look like an earthling to me.

BE: The same principles are applied in environmental remote sensing. And, I like to study analogous environments on Mars, like Iceland and Hawaii, that are in some ways Mars-like.

NA: Getting back to the methods, it sounds like CRISM was the major technological advance that made this work possible. Is that true?

BE: CRISM has certainly been a big advance, but it stands on the shoulders of giants (e.g. OMEGA). It's generally true that as we look at Mars at higher and higher resolution, the more interesting it gets--especially in terms of the history of water.

NA: How long have OMEGA and CRISM, respectively, been in operation?

BE: CRISM was launched in '05 and has been imaging Mars since September '06. OMEGA entered orbit in December 2003.

NA: Are many other scientists aquiring data from CRISM (and publishing that data)?

BE: Absolutely. CRISM is a team effort with folks at APL, Brown, Wash U, and various NASA centers. There's another Science paper coming out the first week of August. And, quite a few more in the works. We've been making the rounds at conferences.

NA: Is everyone interested in water?

BE: Well, the water and life question is a big one. But there's a diversity study too. Several folks study the seasonal evolution of the polar caps, the composition of the atmosphere and climate. Other folks are interested in igneous minerals that give clues as to the evolution of Mars' interior.

I like to think that by figuring out how Mars works and why its different from Earth we learn a lot about how our own planet works.

NA: Does this even help us understand pressing issues on Earth like climate change?

BE: I think we gain a better understanding of how climate works--which processes are important and which aren't. For example, Mars was once warm and wet. Why it's climate changed so profoundly we don't really understand.

NA: I see. You were also the fourth author on a paper published this month in Nature, entitled "Hydrated silicate minerals on Mars observed by the Mars Reconnaissance Orbiter CRISM instrument." Was this study closely related to the other paper?

BE: Very tightly. We actually wrote and submitted this one first but in the vagaries of the publishing process it came out second. This Nature paper is the big picture paper on clays from CRISM

NA: So, what's the gist of this one, and how is it unique from the paper we were talking about earlier?

BE: Well, the Mustard et al. Nature paper provides the big picture global view of clays. Like OMEGA before us, CRISM finds clays are restricted to the oldest terrains on Mars (> 3.5 billion years). What's different is that we see much more clays.: 1000's of exposures over the whole southern part of the planet and much more diversity in the chemistry of the clays.

They indicate clays (and thus water which created them) were more pervasive than previously thought. And, the variety of minerals suggests there were multiple "flavors" of watery environments: some underground, some at the surface, some with a lot of leaching, some with just a little.

NA: The last sentence of the abstract boldly states "These results point to a rich diversity of Noachian environments conducive to habitability." Does this mean conducive to habitability for life?

BE: That's right. We see ancient Mars as place that had a lot of water. On Earth, we tend to find life where we find water.

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Make sure you check out the second part of the interview, published here.

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Ehlmann, B.L., Mustard, J.F., Fassett, C.I., Schon, S.C., Head III, J.W., Des Marais, D.J., Grant, J.A., Murchie, S.L. (2008). Clay minerals in delta deposits and organic preservation potential on Mars. Nature Geoscience, 1(6), 355-358. DOI: 10.1038/ngeo207

Mustard, J.F., Murchie, S.L., Pelkey, S.M., Ehlmann, B.L., Milliken, R.E., Grant, J.A., Bibring, J., Poulet, F., Bishop, J., Dobrea, E.N., Roach, L., Seelos, F., Arvidson, R.E., Wiseman, S., Green, R., Hash, C., Humm, D., Malaret, E., McGovern, J.A., Seelos, K., Clancy, T., Clark, R., Marais, D.D., Izenberg, N., Knudson, A., Langevin, Y., Martin, T., McGuire, P., Morris, R., Robinson, M., Roush, T., Smith, M., Swayze, G., Taylor, H., Titus, T., Wolff, M. (2008). Hydrated silicate minerals on Mars observed by the Mars Reconnaissance Orbiter CRISM instrument. Nature, 454(7202), 305-309. DOI: 10.1038/nature07097