Mars analog minerals’ spectral reflectance characteristics under Martian surface conditions

Abstract We investigated the spectral reflectance properties of minerals under a simulated Martian environment. Twenty-eight different hydrated or hydroxylated phases of carbonates, sulfates, and silica minerals were selected based on past detection on Mars through spectral remote sensing data. Samples were ground and dry sieved to 2 fed). Reflectance spectra from 0.35 to 4 µm were taken periodically through a sapphire (0.35–2.5 µm) and zinc selenide (2.5–4 µm) window over a 133-day period. Mineral stability on the Martian surface was assessed through changes in spectral characteristics. Results indicate that the hydrated carbonates studied would be stable on the surface of Mars, only losing adsorbed H 2 O while maintaining their diagnostic spectral features. Sulfates were less stable, often with shifts in the band position of the SO, Fe, and OH absorption features. Silicas displayed spectral shifts related to SiOH and hydration state of the mineral surface, while diagnostic bands for quartz were stable. Previous detection of carbonate minerals based on 2.3–2.5 µm and 3.4–3.9 µm features appears to be consistent with our results. Sulfate mineral detection is more questionable since there can be shifts in band position related to SO 4 . The loss of the 0.43 µm Fe 3+ band in many of the sulfates indicate that there are fewer potential candidates for Fe 3+ sulfates to permanently exist on the Martian surface based on this band. The gypsum sample changed phase to basanite during desiccation as demonstrated by both reflectance and XRD. Silica on Mars has been detected using band depth ratio at 1.91 and 1.96 µm and band minimum position of the 1.4 µm feature, and the properties are also used to determine their age. This technique continues to be useful for positive silica identifications, however, silica age appears to be less consistent with our laboratory data. These results will be useful in spectral libraries for characterizing Martian remote sensed data.