Gale Crater: Formation and post-impact hydrous environments

Abstract

Gale Crater, the landing site of the 2011 Mars Science Laboratory mission, formed in the Late Noachian. It is a 150km diameter complex impact structure with a central mound (Mount Sharp), the original features of which may be transitional between a central peak and peak ring impact structure. The impact might have melted portions of the substrate to a maximum depth of ∼17km and produced a minimum of 3600km3 of impact melt, half of which likely remained within the crater. The bulk of this impact melt would have pooled in an annular depression surrounding the central uplift, creating an impact melt pool as thick as 0.5–1km. The ejecta blanket surrounding Gale may have been as thick as ∼600m, which has implications for the amount of erosion that has occurred since Gale Crater formed. After the impact, a hydrothermal system may have been active for several hundred thousand years and a crater lake with associated sediments is likely to have formed. The hydrothermal system, and associated lakes and springs, likely caused mineral alteration and precipitation. In the presence of S-rich host rocks, the alteration phases are modelled to contain sheet silicates, quartz, sulphates, and sulphides. Modelled alteration assemblages may be more complex if groundwater interaction persisted after initial alteration. The warm-water environment might have provided conditions supportive of life. Deep fractures would have allowed for hydraulic connectivity into the deep subsurface, where biotic chemistry (and possibly other evidence of life) may be preserved.