Every Thursday, Laboratory Equipment features a Scientist of the Week, chosen from the science industry’s latest headlines. This week’s scientist is James Wray from the Georgia Institute of Technology. He and a team found that Mars is much more geologically complex than believed and has a mineral found in granite, known as feldspar.
Q: What made you interested in studying the chemical makeup of Mars rocks?
A: Ultimately I want to understand whether Mars used to be a more habitable world than it is today. We learned in the 1970s that some of its oldest regions are full of dry river valleys, so that's a good clue. What we've gained more recently is an ability to map the chemistry and mineralogy of Martian rocks and soils, and these show not only that water was there, but also how salty, acidic, hot or cold it was. Or we can look at the chemical makeup of igneous rocks untouched by water, which tell us about the history of volcanism, another key part of understanding how the planet has evolved.
Q: What are the future implications of your research and findings?
A: Our observations can be interpreted a few different ways, but they all imply significant "magma evolution." That is, you didn't just melt the Martian mantle and then recrystallize it at the surface; these rocks require multiple cycles of partial melting and crystallization. Each cycle takes time, implying that Martian volcanoes have been active — at least intermittently — over long periods. There are also implications for the water story. Most igneous rocks on Mars are basalts, and if you start with basalt and end up with, say, the clay mineral kaolinite, that implies a certain duration and pH of aqueous weathering. If you start from something more like a granite and end up with kaolinite — that implies something else. It matters both where you start and where you finish.
Q: What was the most surprising thing you found in your research?
A: What we found was a new spectral signature of feldspar. Feldspar itself is not surprising; in fact it is ubiquitous on Mars. However, this particular signature can only be seen if the feldspar is accompanied by at most 5 percent or less of dark iron-rich minerals. Dark iron-rich minerals are all over Mars, in its basaltic rocks and in its sands, so it was surprising to find places on the surface so depleted of those minerals over scales large enough to see from orbit (dozens to hundreds of meters across, or more). We had not thought to look for this, until we found it serendipitously.
Q: What is the take home message of your research and results?
A: Martian magmas are more diverse than we had thought. This newfound diversity may include granites formed in slowly cooling subsurface magma chambers, or viscous light-toned volcanic domes formed by surface eruptions. Alternatively, some of these rocks could be anorthosites, like the "Genesis Rock" returned from the Moon by Apollo 15, which confirmed that the Lunar highlands formed out of feldspars floating to the top of a primordial magma ocean.
Q: What new technologies did you use in your lab during your research?
A: We used image processing software to analyze the spectral data, and invented a simple method to map these very feldspar-rich parts of Mars. But our crucial piece of equipment is over 100 million miles from my lab. We used the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), an instrument on board NASA's Mars Reconnaissance Orbiter. CRISM uses a diffraction grating to disperse the light from Mars into 544 wavelength intervals, spanning from the blue end of the visible spectrum (360 nm) through the shortwave infrared (four microns). We can map specific minerals based on the distinctive pattern of wavelengths at which they absorb light from the Sun.
Q: What is next for you and your research?
A: Now that we know these rocks exist on Mars — and how to find them) — we'll use CRISM to look for more examples. Observing their spectra at even longer infrared wavelengths with a future high-resolution spectrometer could help to resolve uncertainties about what they are and how they formed. But for definitive answers, we would probably need to land there and obtain ground truth. Add them to the long list of interesting places on Mars that we hope to visit someday!