WIDESPREAD AQUEOUS MINERALIZATION IN OUTFLOW CHANNEL SEDIMENTS AROUND SOUTHWESTERN CHRYSE PLANITIA, MARS (Invited Presentation)

NASA has "followed the water" in its exploration of Mars since the first controlled landing there nearly 50 years ago, in the Chryse Planitia basin downstream of outflow channels Maja/Maumee and Kasei Valles. Fluvial or marine sediments were anticipated in such a setting, but the rocks encountered at the landing site appeared mostly volcanic, a theme that would be repeated across several subsequent Mars landings. This led to speculation that perhaps lava carved the martian flood channels instead of water; such doubts remain even after abundant mineral evidence for water-rock interactions on Mars has emerged, as the mineral vs. morphological traces of past surface water often appear spatially separated from each other.

Here we report orbital identifications of aqueous minerals in light-toned deposits near the mouths of Maja and Kasei Valles. Hydrous silica is enriched in these materials, and the Maja deposits are particularly extensive, with surface exposures spanning ~100 km². In between these two are Maumee and Bahram Valles, which host scattered similar-appearing light-toned layered deposits on their lower channel floors. Combined with our prior identification of hydrous minerals in light-toned layered deposits along Shalbatana Vallis, and the well-documented sedimentary fans (deltas?) at the mouths of Hypanis and Sabrina Valles, these observations collectively support a major role for long-lived aqueous processes in shaping landscape evolution across this region of Mars. Upper Shalbatana Vallis hosts some light-toned layered deposits with clay minerals that may be authigenic, but the less stable silica phases found downstream at Maja and Kasei suggest persistently cold and dry conditions since their formation. These conditions may have optimally preserved any traces of habitable or inhabited paleo-environments at these sites, which are at relatively low latitudes and elevations, making them potentially accessible to future landed missions with the mobility needed to reach the outcrops of interest.