Curious About Life: Interview with Darby Dyar
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.
The Chemistry & Camera (ChemCam) will study Martian rocks and soil in depth. A laser will target selected rocks, creating an ionized, glowing plasma that will be used to analyze their composition. The instrument’s camera will resolve features 5 to 10 times more in-depth than previous rovers. Darby Dyar, of Mount Holyoke College, is one of the scientists using ChemCam to search Martian minerals for hydrogen and water.
What kind of science do you do, generally?
I started out as a field geologist, and now I’m a geochemist. I’m interested in how hydrogen and oxygen evolve on terrestrial planets. I’ve worked on everything from lunar samples to precious gemstones to the geology of the state of Maine to volcanoes in Nevada. All of them share this thread of trying to understand how hydrogen, in particular, and oxygen are distributed between minerals in places in our solar system. I try to determine things like what controlled how much hydrogen ended up in which bodies in the beginning, and then what controlled how hydrogen and oxygen are recycled over geologic time, including by organisms. One of my most exciting projects right now is bio-reduction of iron in minerals by extremophile microbes from the mid-ocean ridges.
For example, some people might tell you that the Moon started out completely dry, and that the only hydrogen on the surface of the Moon has been brought there by comets. Other people might say that the Moon was made of stuff that had hydrogen in it initially, and that the Moon is just continuously losing that hydrogen to outer space, which is why the surface is fairly dry now but only has a trace of hydrogen left.
So there are lots of problems in planetary science that ask the question, is the water endogenous or indigenous? In other words, did it come from somewhere else, or did it come from the interior of the planet? Some people even think that’s true of the Earth, that all of the water that’s here was brought by comets. I think that’s highly unlikely.
I wouldn’t call myself a Mars specialist, but I’m a specialist in thinking about how hydrogen evolved on planets. That’s pretty important for MSL, because it’s important to not just have people who know Mars inside out, but people who can relate the Mars results to other planets, especially Earth.
What it is specifically that you do with MSL?
I’m interested in the geological implications of all of the instruments on MSL, because many of them bear on the question of how is hydrogen distributed, both inside and outside of Mars—in the rock, on the surface, and then in the atmosphere. Many of the instruments in the payload address that question in different ways. My particular expertise as an instrumentation person is in working with the ChemCam instrument. I have a laser-induced breakdown spectrometer in my lab here at Mount Holyoke and we are actively running samples under Mars conditions.
We have a giant, stainless steel vacuum cube with a couple of windows on it. We put samples, a bunch of rocks, inside the chamber on a little merry-go-round, and we pump all the air out of the chamber. Then we put a little bit of carbon dioxide gas in it so that it’s the same pressure as the surface of Mars. We shoot a laser through the window at the rock and generate plasma just the way ChemCam does, and then take a spectrum of the plasma and try to understand the chemistry of the rock based on the spectroscopic signature of that little plasma.
ChemCam has a calibration target on it with nine rock standards and one titanium standard, and we have samples of those in my lab. We can shoot them in my lab, and then compare the results with the results on Mars. Understanding that then allows us to use other data from other rocks that we’ve acquired in my lab to draw conclusions about things that are happening on Mars. So we use the calibration samples as a sort of Rosetta stone to let us go back and forth between lab data and Mars data.
How does your work help us to answer astrobiology questions?
On Earth, life began in the ocean. Our Earth-centric perspective is that, if life began in other places similarly to the way it began here, then we need to look for places where there was standing liquid water. Understanding the history of water on Mars is really the next closest question to understanding where did life evolve on Mars. Of course, that’s what NASA has had as its hallmark for many of these Mars missions, the whole question of follow the water, because follow the water means go to the place where life could have formed.
It’s not simply a matter of looking for puddles or ripple marks. It’s also a question of looking for minerals that form in the presence of water or as signatures of biological activity and the environments in which they form. If life was present on Mars billions of years ago, those signatures are likely to be preserved as hydrous minerals, or minerals with water in their structures, distributed among different habitats.
As astrobiologists, we seek to tease out the interrelationships among varying environmental conditions, the associated microbial phenomena, and the resultant biomarkers. I think answers to important astrobiology questions will come only when we combine the best observations of Martian habitats, careful studies of biomarkers in analogous terrestrial habitats, and clever application of state of the art instrumentation.