A synthesis of Martian aqueous mineralogy after 1 Mars year of observations from the Mars Reconnaissance Orbiter

TLDR

The paper catalogs the various Martian aqueous mineral deposit classes, evaluates origin hypotheses, raises new questions from existing data, and discusses implications for ancient habitable environments. The authors examined and characterized Martian aqueous mineral deposits using MRO’s CRISM hyperspectral data (0.4–3.9 µm) in conjunction with high‑resolution HiRISE and Context Imager imagery. High‑resolution MRO data, combined with TES, THEMIS, and OMEGA observations, reveal that Martian aqueous minerals are diverse and widespread, comprising 9–10 distinct deposit classes—including phyllosilicate‑rich layered blankets, carbonate‑bearing units around Isidis, and hydrated silica‑sulfate strata near Valles Marineris—and suggest that 2–5 Noachian‑aged phyllosilicate/carbonate deposits formed in potentially habitable aqueous environments.

Abstract

Martian aqueous mineral deposits have been examined and characterized using data acquired during Mars Reconnaissance Orbiter's (MRO) primary science phase, including Compact Reconnaissance Imaging Spectrometer for Mars hyperspectral images covering the 0.4–3.9 μ m wavelength range, coordinated with higher–spatial resolution HiRISE and Context Imager images. MRO's new high‐resolution measurements, combined with earlier data from Thermal Emission Spectrometer; Thermal Emission Imaging System; and Observatoire pour la Minéralogie, L'Eau, les Glaces et l'Activitié on Mars Express, indicate that aqueous minerals are both diverse and widespread on the Martian surface. The aqueous minerals occur in 9–10 classes of deposits characterized by distinct mineral assemblages, morphologies, and geologic settings. Phyllosilicates occur in several settings: in compositionally layered blankets hundreds of meters thick, superposed on eroded Noachian terrains; in lower layers of intracrater depositional fans; in layers with potential chlorides in sediments on intercrater plains; and as thousands of deep exposures in craters and escarpments. Carbonate‐bearing rocks form a thin unit surrounding the Isidis basin. Hydrated silica occurs with hydrated sulfates in thin stratified deposits surrounding Valles Marineris. Hydrated sulfates also occur together with crystalline ferric minerals in thick, layered deposits in Terra Meridiani and in Valles Marineris and together with kaolinite in deposits that partially infill some highland craters. In this paper we describe each of the classes of deposits, review hypotheses for their origins, identify new questions posed by existing measurements, and consider their implications for ancient habitable environments. On the basis of current data, two to five classes of Noachian‐aged deposits containing phyllosilicates and carbonates may have formed in aqueous environments with pH and water activities suitable for life.