Leah Hutchison Roach

Diverse mineralogies in two troughs of Noctis Labyrinthus, Mars

Two troughs in Noctis Labyrinthus display a diversity of mineral assemblages rarely seen spatially collocated on Mars. Minerals identified from Mars Reconnaissance Orbiter data within the troughs include polyhydrated and monohydrated sulfates, an Al clay (e.g., kaolinite or beidellite), Fe/Mg smectites, hydrated silica and/or opal, and a leached clay or jarosite mixture with a doublet absorption between 2.2 and 2.3 μm. Units both pre-date and post-date smaller pits and depressions within the larger troughs, indicating that deposition was coeval with continued extension, collapse, and erosion in the Late Hesperian to Early Amazonian (2–3 Ga). The strata within each trough display a mineralogic diversity consistent with active aqueous processes and/or changing chemical conditions over time, perhaps due to hydrothermal alteration of volcanic ash, influxes of groundwater from nearby Tharsis volcanism, fumarole activity, and melting snow and/or ice. The superposition of younger Fe/Mg smectites over sulfates, Al clays, and hydrated silica and/or opal in both troughs indicates that this region is unique relative to most other locations on Mars, where the opposite progression is observed and the Fe/Mg smectites are Noachian (older than 3.6 Ga) in age. Consequently, these troughs may have been habitable regions on Mars at a time when drier conditions dominated the surface.

Key Scientific Questions and Key Investigations from the First International Conference on Martian Phyllosilicates

Minerals and their occurrences can tell us about the chemistry, pressure, and temperatures of past environments on Mars and thus allow inferences about the potential for habitability. Thanks to recent space exploration, a new vision is emerging wherein Mars hosted environmental conditions of potential astrobiological relevance. This epoch is identified by the presence of phyllosilicate-bearing deposits, which are generally contained in very ancient basement rocks. In October 2008, over 100 planetary scientists representing 11 countries met in Paris to assess and discuss the relevance of martian phyllosilicates. The conference was structured to promote the discussion and debate of key scientific questions and key essential investigations. The purpose of this report is to document the current state of knowledge related to martian phyllosilicates and to ascertain which questions remain to be addressed: What are the basic characteristics of the phyllosilicate minerals on Mars? What are the genetic mechanisms by which phyllosilicate minerals have formed on Mars? What is the relationship between the phyllosilicate minerals observed in martian meteorites and those detected from orbit? What are the implications of phyllosilicate-bearing rocks for the development of prebiotic chemistry and the preservation of biosignatures? The most promising investigations to address these questions are presented.