Quenched glass formed by hypervelocity impacts can encapsulate and preserve biosignatures on Earth, demonstrating the fossilization potential of glass-rich impactites on Mars. However, definitive spectral signatures of impact glass have not been identified on the martian surface from orbital remote sensing. Here we present a remote compositional survey of probable impactites in well-preserved craters, using data from the Compact Reconnaissance Imaging Spectrometer for Mars. These units are composed of mafic glasses mixed with crystalline phases including olivine and pyroxene, determined by radiative transfer Hapke modeling followed by spectral mixture analysis. This glassy material likely formed from impactinduced melting of the target rock with rapid quenching and minor subsequent devitrification or chemical alteration. The metastable glass has been preserved by the cold and dry martian climate during the Amazonian period, and this preservation—as confirmed here across the planet—provides a means to trap signs of ancient life on the accessible martian surface. Our results lend concrete support to theoretical arguments suggesting that impact glass has formed in abundance on Mars, both inside of craters and as spherules in distal strewnfields. Contrary to previous ideas, martian impact products are not destroyed by interaction with volatiles during the impact process.
- Received 20 February 2015.
- Revision received 8 May 2015.
- Accepted 9 May 2015.
- © Geological Society of America