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The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. CitationHamilton, V.E., et al., "Evidence for widespread hydrated minerals on asteroid (101955) Bennu." Nature astronomy 3, 4 (2019): p.

[1] Columbus crater in the Terra Sirenum region of the Martian southern highlands contains light-toned layered deposits with interbedded sulfate and phyllosilicate minerals, a rare occurrence on Mars. Here we investigate in detail the morphology, thermophysical properties, mineralogy, and stratigraphy of these deposits; explore their regional context; and interpret the crater's aqueous history. Hydrated mineral-bearing deposits occupy a discrete ring around the walls of Columbus crater and are also exposed beneath younger materials, possibly lava flows, on its floor. Widespread minerals identified in the crater include gypsum, polyhydrated and monohydrated Mg/Fe-sulfates, and kaolinite; localized deposits consistent with montmorillonite, Fe/Mg-phyllosilicates, jarosite, alunite, and crystalline ferric oxide or hydroxide are also detected. Thermal emission spectra suggest abundances of these minerals in the tens of percent range. Other craters in northwest Terra Sirenum also contain layered deposits and Al/Fe/Mg-phyllosilicates, but sulfates have so far been found only in Columbus and Cross craters. The region's intercrater plains contain scattered exposures of Al-phyllosilicates and one isolated mound with opaline silica, in addition to more common Fe/Mg-phyllosilicates with chlorides. A Late Noachian age is estimated for the aqueous deposits in Columbus, coinciding with a period of inferred groundwater upwelling and evaporation, which (according to model results reported here) could have formed evaporites in Columbus and other craters in Terra Sirenum. Hypotheses for the origin of these deposits include groundwater cementation of crater-filling sediments and/or direct precipitation from subaerial springs or in a deep (∼900 m) paleolake. Especially under the deep lake scenario, which we prefer, chemical gradients in Columbus crater may have created a habitable environment at this location on early Mars.

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[1] A subset of the sinuous ridges (SRs) in the Aeolis/Zephyria Plana (AZP) region of Mars has been previously hypothesized to be inverted fluvial features, although the precise induration and erosion mechanisms were not specified. Morphological observations and thermal inertia data presented here support this hypothesis. A variety of mechanisms can cause inversion, and identification of the specific events that lead to fluvial SR formation can provide insights into the sedimentological, geochemical, and climatic processes of the region. Reconnaissance of two terrestrial lava-capped ridges suggests some criteria that may be used to identify inverted fluvial features formed by lava infill on Mars, but these criteria are not satisfied by the majority of the AZP fluvial SRs. Armoring also appears inconsistent with terrestrial analogs. Layering and surface textures of fluvial SRs indicate that the most likely induration mechanism was geochemical cementation of fluvial sediments, and that the primary erosional mechanism that exposed the fluvial SRs was aeolian abrasion. This analysis of formation mechanism provides a foundation for estimating paleodischarge using an empirical form-discharge approach, to which we have applied scaling, for Martian gravity. For those fluvial SRs meeting a set of criteria for accurate paleodischarge estimates, paleodischarge values generally range between 10 1 and 10 3 m 3 s −1. The largest of these initial estimates are comparable to paleodischarge estimates for some late-stage Noachian fluvial channels on Mars, and provide a constraint on the atmospheric conditions at this equatorial location during the late Hesperian to early Amazonian time frame.