TEMPORAL VARIATIONS OBSERVED IN SPECTRA OF ACTIVE FEATURES ON MARS

Long term observations of the Martian surface by multiple orbiters show evidence for a variety of slope features that are active in the present day climate. While orbiter data shows clear evidence of geomorphic change and activity, in many cases, the underlying mechanism, any volatile chemical constituents involved, and the cause of the change is debated. We considered five different active slope features: (i) classical bedrock gullies, (ii) linear dune gullies, (iii) bright gully deposits, (iv) dark slope streaks, and (v) recurring slope lineae (RSL), for which both wet and dry formation mechanisms have been proposed. We examined data from Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) for all of these features to better understand their chemical or mineralogical composition and formation mechanism. We seek to understand the chemical nature of these changes by looking for temporal variation observed in their spectra. RSL display distinct and consistent spectral signatures of ferric and ferrous minerals at most sites, and exhibit temporal fluctuation in their spectra where the signature of distinct absorption bands varies as a function of season (Ojha et al., 2013, GRL). We seek to understand if such time-varying spectral fluctuations, which have been cited as evidence for wet flow, can be observed for any of the other slope features. Preliminary results suggest that these signatures are unique to RSL, with other slope features showing no clear spectral distinction from surrounding slope materials, although CO₂ and H₂O frosts are spectrally evident at many gully sites. We also present results from radiative transfer modeling to look into the effect of atmospheric conditions on our interpretation of spectral changes at RSL sites.