Curious About Life: Interview with Jennifer Stern
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 Sample Analysis at Mars (SAM) instrument is actually a combination of three individual instruments that will investigate the chemistry of the Martian surface. Roughly the size of a microwave oven, SAM will analyze samples taken by the robotic arm, looking for organic and inorganic compounds.
Jennifer Stern is one of the scientists using SAM to sort out geological signatures in the rock record from potential biological processes.
What kind of science do you generally do?
I am a geochemist. Actually my doctoral work did not involve space science at all. I use chemical tracers to understand the cycling of nutrients and elements, particularly those that are relevant to life as we know it. There’s carbon, nitrogen, oxygen, sulfur, phosphorus. In graduate school, I used these kinds of techniques on Earth to examine things such as, how organisms process carbon and phosphorus in the Everglades, and how we trace methane emissions in landfills.
Biological processes can leave marks on their environment in the form of altering it chemically. They alter the concentrations of different elements, or isotopes, and these patterns can be different from the patterns that geological processes leave. I’m trying to use the things like the concentrations and the isotopic composition of elements to look at geologic versus biological processes.
For example, in the sedimentary record on Earth, you can use things like carbon isotopes, oxygen isotopes, and the distribution of trace elements to say something about the kinds of geological processes that formed the rock and, sometimes, whether there may have been biological processes involved.
For example, on Earth, there are different environments that have geology that we think might be similar to Mars. We can go to these sites and study the processes that occurred there, past and present, to understand better what may have happened to shape similar geology on Mars. For example, we’ve done field work in Svalbard, Norway, and used some of the techniques used on Curiosity to look at, for example, mineralogy, organic content, and carbon and oxygen isotope composition of different rocks. We looked at carbon that formed in two very different environments by two different processes. One was a fossilized methane seep, which may or may not be relevant to Mars, and one was a volcanic vent system encrusted by carbonates that were formed in association with the eruption of material through a glacier.
So basically we’re looking at different forms of carbon and other biologically relevant elements, how they’re recorded in the rock record, and what their isotopes may have to say about the processes that cycled them. It’s never a smoking gun type of thing; it’s not like we get a certain isotopic signature of carbon or oxygen and that says yes or no to life, but it helps tell us how this carbon may have been processed. Was it processed geologically? Was it processed from some other mechanism that looks different than geology?
What do you do specifically for MSL?
I am part of the Sample Analysis at Mars team. We’re based out of NASA-Goddard, but our instrument has contributions from JPL and from France, as well. We have an international and bi-coastal team.
SAM is possibly the most complex instrument on the rover. There are a lot of different experiments, from measuring elemental concentrations in the atmosphere to measuring the composition of gases involved when we heat up a solid sample like a rock sample or a soil sample. From these gases, we are looking for things like the isotopic composition of water or carbon that might be in the rock. We’re also able to detect organic molecules should they be present.
I’ve been involved in optimizing some of the experiments that we run on SAM. In the lab at Goddard, we analyze Mars analog samples—Mars-like rocks—to optimize these measurements, and try to understand them as they would be made on Mars.
Specifically, one of my interests is the evolved gas analysis. When you heat up the rock, you evolve gases that are sent into the mass spectrometer, where molecules are identified by their masses. The mass information and the temperatures at which different gases are evolved from the rock tells us about minerals and possible organics in the rock. If you evolve water or carbon, CO2, during heating of the rock, you can send this gas into the tunable laser spectrometer, an instrument on SAM that was developed at JPL. The really cool thing about that instrument is it can measure the isotopic composition of the CO2, and the water coming off of a rock.
I’m interested in what that data means. If we do the same kind of experiment to rocks on Earth, we can determine whether the rocks are carbon-rich or carbon-poor, or have minerals that formed in water. What does it mean if we find a variation in the isotopic composition of the carbon and the oxygen that’s coming off of the rock? From that, you can establish past atmospheric, past environmental, possibly hydrological cycle information. If you’re lucky enough to find organic carbon, you may be able to get information about whether that organic carbon was formed by a geological or a biological process.
The other thing that I do, as part of the SAM and the larger Curiosity team, is that I represent SAM when I’m involved in all the discussions as we get data down from Mars. We develop hypotheses from the data we receive from all 10 instruments on Curiosity, and see where SAM can complement other geochemical measurements. We try to make decisions on what samples should we target for analysis by SAM; where is the best place to look for preservation of organic molecules?
We think with Gale Crater that we’ve found somewhere that might be an environment friendly to the formation of organic molecules and that maybe their creation would have been preserved. So I help the other MSL science team members to understand the full capabilities of SAM and how it can be used, and then, as a SAM team member, I help understand and optimize the measurements that SAM makes.
How does your work help to answer astrobiology questions?
My expertise has come from looking for the way life makes its presence known in Earth’s present environments and in the past rock record. When I did these experiments on Earth, I was looking at metabolic processes and how carbon isotopes behave when CO2 or methane is taken up or produced by organisms. For example, when we would look at methane emissions from landfills on Earth, we look at the carbon isotopic composition of the methane. That gives us an idea of how much bacterial activity occurred and how much this methane was being converted into CO2.
By using these techniques originally developed to look at biogeochemical processes on Earth, we can try to look at different processes on other planets. Even though we have not, to date, found "life" on other planets, we’re trying to answer the question more about the processes that govern the transfer of carbon and other elements on other planets, and determine whether it’s a geological process.
It’s actually hard sometimes to tell whether organic molecules on Earth were made geochemically or biologically. On Mars, it’s even more complicated because we have a limited number of scientific observations we can make, so we have to choose carefully which samples might give us the most scientific return. Fortunately, we have both instruments that can tell us a lot about mineralogy and the chemical composition of these rocks, and then we have all these imaging instruments that can tell us about textures and about the larger geological environment where the rocks that we’re looking at may have formed. So we’re able to use the techniques used by SAM in tandem with other techniques to better characterize an astrobiological search.
On Curiosity, we have a couple things that make the mission different than previous missions. One of them is that we have larger and more capable scientific payload than ever before. Also, we had the advanced knowledge from remote sensing to choose a site that we thought had the geology and geochemistry to possibly be a habitable environment in the past, and we had the ability to pinpoint that site and land there. Finally, in terms of astrobiology, we also have the benefit of having gone to Mars several times in the past—Viking, Pathfinder, the MER missions, Phoenix. We’ve learned not only information about the surface and atmosphere, but we’ve also learned how to make the measurements on the surface of Mars better, to actually optimize them and make them more robust, and to target these questions of habitability in a better way.
I don’t think a lot of people realize this, but every time we go to Mars or anywhere else in the whole solar system, the resulting technological advances have an impact here on Earth. I think sometimes this is not well communicated to the public. I think one of the great things about these missions is that not only are we gaining information about another planet and stimulating kids and other people to be excited about science, but there are also life-saving and progress-enabling innovations, such as improvements in the detection and treatment of diseases like cancer and diabetes, and miniaturized robotics and lasers that have vastly improved micro-surgery on the human brain, heart, and eye. Ultra precise GPS and high precision robotics stemming from NASA research has allowed remote controlled devices to be deployed in military and civilian operations too dangerous for humans. Innovations in NASA supercomputing related to modeling Space Shuttle fuel pumps has been used by surgeons in the development of a ventricular assist device that provides a “bridge to heart transplant” to keep heart transplant candidates alive while waiting for a donor. Many of us, including myself, don’t often think about how much of the basic technology we use everyday has roots in NASA missions.
One of my favorite NASA Spinoffs is the low cost, lightweight parachute developed through a partnership between NASA Langley Research Center and small business BRS Aerospace. It lowers small airplanes to the ground in emergencies – the pictures of planes hovering in the air via enormous parachutes are amazing. So now we have huge supersonic parachutes that can lower a Mars rover weighing a ton to the surface of Mars, and parachutes lowering entire airplanes to the surface of Earth. I think that’s pretty cool.