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Mysteries on Mars

by Usha Sutliff sutliff@usc.edu

Kenneth Nealson, co-principal investigator of the THEMIS project.

Photo by Irene Fertik

A camera system aboard the Mars Odyssey that uses infrared to identify minerals is transforming the way scientists think about the Red Planet.

In place of the bland, uniform landscape many expected, the Thermal Emission Imaging System, or THEMIS, has revealed a complex topography rich with rocky layers, lava flows and impact craters.

Kenneth Nealson – co-principal investigator of the THEMIS project and holder of the Wrigley Chair in Environmental Sciences in the USC College of Letters, Arts & Sciences – said findings published recently in the journal Science may surprise some and discourage others who hope to find life on Mars.

The findings also may enable scientists to trace the history of the solar system as never before.

The Mars Odyssey, managed by NASA’s Jet Propulsion Laboratory in La Canada Flintridge, was launched on April 7, 2001 and arrived at Mars on Oct. 24 of that year.

The bread box-sized THEMIS is one of three spectrometers aboard the spacecraft. It uses the visible and infrared parts of the spectrum to determine the distribution of minerals on the Martian surface.

During the Martian day, or sol, minerals on the surface of the planet are heated by the sun and – in a process called thermal inertia – radiate the heat back to space.

THEMIS uses nine bands in the infrared spectrum to capture the “fingerprints,” or heat signatures, of the minerals. Each mineral, be it a silicate, sulfate or phosphate, shows up as a different color in the infrared spectrum. The system’s other camera takes pictures in visible light.

The data collected by the two cameras will provide scientists with an unprecedented level of detail about the Martian surface that will help determine where to land future probes and, most importantly, where to search for life.

The first THEMIS results were published in the June 6 edition of Science in a paper written by Philip Christensen, an Arizona State University professor of planetary geology and the project’s principal investigator.

Nealson’s real involvement in the project is yet to come. As an astrobiologist, his job will be to determine what the potential for life is or could once have been.

Q: When you speak of life on Mars, what are you looking for exactly?

A: To the chagrin of almost everyone, it is now clear that there are no large life forms on Mars – no plants, no animals, nothing obvious. So the search has turned to microbes. I would be absolutely happy to find anything that resembled primitive microbial life. But it will not be easy.

You have to be like Sherlock Holmes. When he searched for a culprit, everything was an inference. It’s forensics. If you’re lucky enough to see the culprit, then the search is over.

Now, instead of looking for a footprint in the sand, we’re looking for the footprint that bacteria left behind. That’s a greater challenge because it’s really small and bacteria don’t leave fossils behind. Since these creatures are so small and have no hard parts, it’s a huge challenge. We have to be clever.

Q: What are the most significant findings detailed in this paper?

A: The major finding is that there are layered terrains on Mars that look as if you can trace the geology of the planet through a few phases. That’s an interesting and very critical finding in terms of whether or not there was ever life on Mars.

Mars has no plate tectonics, so Mars doesn’t constantly eat itself up like Earth. On Earth, we really can’t tell much about the history of the solar system because most of it has been obscured by our planet’s tectonic activity.

But in the absence of plate tectonics, maybe the best history of the solar system we have is sitting on Mars. So to know that you might be able to go back and find these layered terrains – if we ever get people to Mars, or bring back the right kinds of samples – is fabulous.

Q: What else did they find?

A: To me, one of the most stunning findings so far is the thick layers containing olivine. Olivine is one of these minerals that is unstable in the presence of water over geological time. It tends to erode very fast and disappear over time. So when you find huge expanses of olivine, you would think that there wasn’t any water around. That’s the easiest explanation why you find olivine any place.

In some areas, the olivine is 50 to 100 meters thick. What it says is that there’s no subsurface weathering. There’s no water flowing through that would have weathered the olivine, and it also says that since this area was exposed, there was no water there.

This doesn’t prove that there’s no groundwater on Mars, but it proves that in that place – the Ganges Chasma – there wasn’t any “wet weathering” either before or after this surface was exposed. That’s a fairly discouraging thing. If you keep finding olivine in these kinds of areas, you’ll get more and more discouraged that there’s no major water cycle on Mars. If you’re holding out for any kind of life, it would be a real tough one to swallow.

Q: As an astrobiologist, are you disappointed by this?

A: Not particularly. Our goal is not to find life everywhere we go, but rather to understand why it exists or doesn’t exist in various places. So I feel very objective. We have to frame the search for life on Mars in a way that if we don’t find it, we still learn a lot about the planet.

You measure chemistry and physics and geology and you infer biology from the results. Then if there isn’t any life, you’ve still learned the chemistry, physics and geology and you feel really good about the mission.

That would help when you come to another planet. You’d recognize it. You’d say, “Ah, this looks like Mars. It’s not a very good habitat for life.” Or, if we find life on Mars, you would say the opposite.

I’ve always felt these things are not incompatible. We shouldn’t bet all our chips on finding life. We should bet all of our chips on doing good science.

I always say to people in my astrobiology group: “Doesn’t it seem a bit much to hope for that the first place we’d go in the entire universe would have life too?”

From my perspective, it’s a lot to hope for. We know that the origin and evolution of life are very complex processes and to imagine that two planets side by side in the universe with very different characteristics would do the same thing is really wild. I wouldn’t bet against it. I just wouldn’t bet for it.

Q: How will these data guide the search for life?

A: There are thousands of square kilometers that look as if they’re covered with many meters of dust that has not moved since it was laid down. There’s nothing jutting out of it. It’s just there, uniform.

This infrared technique allows scientists to tell when they’re looking at rock and when they’re looking at dust. People interested in studying the geology or potential biology of a planet are probably less interested in studying dust.

Q: So it will help them avoid the geologically poor areas?

A: Exactly. We now know some areas that are probably not top choices. If you’re interested in the potential for life, you wouldn’t want to study the dust. If you’re looking for fish, you don’t go to the Sahara desert. This should help define the search space for life and for planetary geology.

The last finding, which addresses the topic of temperature anomalies, is a progress report. We were looking for some temperature anomalies on the surface that couldn’t be explained, a place some warm mantle was coming up and heating. This is one of the things that everybody hoped would show up.

So far there’s nothing that we’re seeing that can’t be explained by thermal inertia – nothing even hints at any inner-heating processes.

Q: So these findings neither bolster nor disprove the argument for life on the Red Planet?

A: If I had to identify one thing in these findings that was encouraging or discouraging for life, the olivine would be it. That, as strange as it seems, is the most discouraging. If such findings continue around the Red Planet, the interest may focus more on the geology and its contribution to the history of our solar system, and perhaps the search for fossils or biosignatures of some past life that may have once thrived on Mars.

Contact Usha Sutliff at (213) 740-0252.

Mysteries on Mars

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