Curious about Life: Interview with Jeff Moersch
The Mars Science Laboratory Curiosity rover has 10 science instruments, and each will be used in the coming weeks and months to help characterize the environment of Mars and determine if the planet ever had the potential for life.
I'm a Mars researcher. I specialize in remote sensing. This is my sixth Mars mission; a lot of my work is with missions. Other than that, I do field work on Earth. I do a lot of terrestrial analog work, places like the Atacama desert and the Andes in Chile, the Mojave desert, and Death Valley.. I also have an interest in instrumentation, so I've had some grants to build prototype instruments for missions.
So what's your favorite terrestrial analog to travel to?
Well, it really depends on what you're trying to study. There's no perfect analog, so you've got to pick which aspect of it you're trying to replicate and then select from there. I really like working in the Atacama a lot. It's a very unspoiled desert in a lot of the places we go. Death Valley is fantastic, too, of course.
You said this is your sixth Mars mission, so what is your favorite Mars mission?
Favorite Mars mission? I don't want to play favorites. Right now, this one is full of potential, I would say, but the one I worked on before this was demonstrated potential. That one was just a blast. That was the Mars Exploration Rovers, Spirit and Opportunity. This one, I think, will get there. It's kind of slow at the beginning, because we take a while to do all the instrument check-outs. Right now, they're checking out the arm. The site we're at is spectacular. I think once we really get going, this will be just as exciting as Spirit and Opportunity were.
That's one thing that I think the general public have a hard time appreciating is how slow this process can be. We land and they expect to see instant results on the news that night, and it just does not work that way. You have to be very patient.
What do you do, specifically, with MSL?
I'm working on an instrument called DAN, which stands for Dynamic Albedo of Neutrons. It's an instrument that was contributed by the Russian space agency, IKI. You can think of it as a hydrogen detector for the subsurface. As we drive along, the instrument measures the energy of neutrons leaking out of the ground. This tells you how much hydrogen is underneath the rover. You can think of the detector footprint as being a hemisphere, about two or three feet in radius, right underneath the rover. So as we drive, we stop, make a measurement, stop, make a measurement, etc., and in doing so, we build up a profile of subsurface hydrogen abundances along the traverse route.
There are lots of hydrogen-bearing minerals. The more common ones that we might expect to find in this location on Mars would be clays, which have a lot of H2O in their structure, and also OH. There's also hydrated sulfates, like gypsum, that have H2O in them. Zeolites have water in them. There's a whole range of minerals that form in liquid water that end up incorporating H into their structure.
DAN has two operational modes: an active mode and a passive mode. Passive mode works the same as neutron detectors that we have had in orbit around Mars before. It relies on the fact that cosmic rays are zipping around in space. Cosmic rays are very high-energy particles, mostly protons, traveling at some appreciable fraction of the speed of light. They come from the Sun and from the galaxy. On a planet that has a very thin atmosphere like Mars, they rain down on the surface. On Earth they don't make it to the surface because the atmosphere is thick enough to stop them. On Mars, they actually make it through the thin atmosphere and bombard the surface.
When they get to the surface, these high-energy protons and cosmic rays will strike the nuclei of any atoms that are in the surface, and this really gives them a wallop. When that collision occurs, it knocks neutrons out of the nucleus in a process called spallation. These neutrons are moving very fast, and they rattle around, bouncing off the different nuclei in the surface. If the nuclei that they bounce against are heavier than neutrons, then every time a neutron bounces against a heavy nucleus, it just bounces back off at about the same speed that it came in at. But if the nuclei the neutrons bounce against are of comparable mass to the mass of a neutron, then it's kind of like a pool ball hitting another pool ball: every time there's a collision, the neutron gives up about half of its speed. If this happens enough, the population of neutrons that was initially going very fast can be significantly slowed down, or “thermalized” by the time the neutrons leak out of the surface, where they can be measured by DAN.
We also have something that's unique in this instrument that we don't have in orbit: we brought with us a tiny little particle accelerator. It's about the size of a shoebox. It's pretty neat. I actually bought one to do experiments. They're made in Moscow. There are two normal uses for these things. One is as triggers for nuclear warheads, because neutrons are needed to set off nuclear bombs. The other thing they use them for is in oil wells. They put these little particle accelerators down the oil well to generate neutrons, and then you look at the leaked neutrons coming back out to tell if there are hydrocarbons down there, because of course oil has hydrogen just like water does. So these are used a lot by the oil companies.
So this accelerator on DAN sends out a very short— one microsecond— and intense pulse of neutrons. Those high-energy neutrons get shot into the ground, and they leak back out just like the ones that are made by the cosmic rays through spallation. Except in this case, you can look at the timing of the slowed neutrons that leak back out relative to the time of the pulse. What that gets you, in addition to the bulk hydrogen abundance, is the vertical distribution of hydrogen. The neutrons that come back first are from the shallow layers, because they're closer and they don't have to travel as far. The ones that come back later are the ones that are coming from deeper.
It's a neat experiment. It's pretty clever. I take no credit for the design. That was all the Russians.
In November, NASA selected a bunch of additional scientists for the mission, including myself. There's three or four of us American scientists, who are working with this Russian-contributed instrument. The Russians have their own team, and we've been brought on to work with them. We help them interface with the rest of the spacecraft being run out of JPL.
How could your work help to answer astrobiology questions?
Well, these minerals that I was talking about, like clays or hydrated sulfates, they all form in specific environments, environments that have an aqueous history. One of the main goals of the mission is to search for potential habitats for past life.
It's not a life detection mission. It's not likely to identify actual life or fossil life. What it's designed to do is look for evidence of places that would have been hospitable to life. When we find these minerals that form in the presence of liquid water, that's one of the key ingredients you would need in a habitat. Finding these habitats addresses the overall mission goals, which are very astrobiologically oriented.