“The eyes are the mirror of the soul,” as the saying goes. A chemist’s version of this saying would probably sound like: a spectrometer is the mirror of chemical composition. Recently, exciting news was brought to our planet by a spectrometer gazing at Mars.
A research paper* published by a group of American scientists in Nature Geoscience at the end of September reported evidence of hydrated salts in Martian lineae (long markings on the planet’s surface). This finding and previously discovered seasonal variations of these geological features are the strongest evidence supporting the existence of liquid water (albeit in a form of brine) on Mars. One might wonder how those hydrated salts were detected and identified. A short answer is by an imaging spectrometer operating on an unmanned space vehicle. A longer answer would be that the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), one of the three advanced imaging systems on the Mars Reconnaissance Orbiter, was able to obtain reflectance spectra of the lineae which matched spectra of hydrated magnesium chlorate, hydrated sodium, and magnesium perchlorates. Obtaining these results was made possible by an impressive scientific and engineering effort.
Reading the description of the CRISM system design and performance is a treat and an inspiration (check out short and long scientific publications and a dedicated website). CRISM is an apparatus the size of a small microwave oven, equipped with a ~1-foot-long telescope and able to obtain spectrally resolved images of the entire surface of Mars (~1/4 of the Earth’s surface area). Building CRISM took nearly 5 years after the selection of the initial proposal. Small dimensions of the apparatus as well as the demanding and conflicting performance requirements demanded innovative solutions. For example, closely placed parts of the spectrometer required low power consumption and specific operational temperatures, which differ by as much as 150°C. This challenge is similar to asking a friend, “Keep a pot of water boiling and an ice cube frozen on a dinner plate, while keeping the plate at room temperature, and using no more electricity than a Christmas tree bulb” (as nicely put on the CRISM web site). The solution to this problem was made possible by inventing a new cryogenic cooler for one of the instrument detectors in addition to the overall design in which different zones of the instrument naturally radiate heat at different rates.
Discovery of hydrated salts on Mars highlights the progress in space exploration and the levels of sophistication reached by present day scientific equipment. It is also important to realize that there is always a collective effort of numerous people behind each of those steps. For example, the CRISM team was comprised of nearly 80 people, which exemplifies an extreme degree of collaboration and consultation. Finally, it is delightful to point out that the lead and the second authors on the Nature Geoscience paper are current graduate students at Georgia Tech. This realization teaches us yet another lesson from discoveries on Mars for fellow graduate students: think beyond the “sky-is-the-limit” paradigm and dream big.
*The paper “Spectral evidence for hydrated salts in recurring slope lineae on Mars” by Lujendra Ojha and colleagues was published in Nature Geoscience, a journal of Nature Publishing Group.
Image courtesy of NASA. Original caption: “With the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument just above his head, a technician at NASA’s Kennedy Space Center works on the Mars Reconnaissance Orbiter spacecraft in July 2005.”
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