Abstract The Martian surface is cold, dry, exposed to biologically harmful radiation and apparently barren today. Nevertheless, there is clear geological evidence for warmer, wetter intervals in the past that could have supported life at or near the surface. This evidence has motivated National Aeronautics and Space Administration and European Space Agency to prioritize the search for any remains or traces of organisms from early Mars in forthcoming missions. Informed by (1) stratigraphic, mineralogical and geochemical data collected by previous and current missions, (2) Earth's fossil record, and (3) experimental studies of organic decay and preservation, we here consider whether, how, and where fossils and isotopic biosignatures could have been preserved in the depositional environments and mineralizing media thought to have been present in habitable settings on early Mars. We conclude that Noachian‐Hesperian Fe‐bearing clay‐rich fluvio‐lacustrine siliciclastic deposits, especially where enriched in silica, currently represent the most promising and best understood astropaleontological targets. Siliceous sinters would also be an excellent target, but their presence on Mars awaits confirmation. More work is needed to improve our understanding of fossil preservation in the context of other environments specific to Mars, particularly within evaporative salts and pore/fracture‐filling subsurface minerals.

Noachian

Hesperian

Geologic record

Siliciclastic

10.1029/2017je005478

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Citations (111)

Testable Hypotheses for Opportunity's Traverse from Santa Maria to the Rim of Endeavour Crater

LPI (2011)

A. A. Fraeman R. E. Arvidson S. L. Murchie F. P. Seelos J. A. McGovern

Traverse

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Citations (1)

Spectral Diversity of Rocks and Soils in Mastcam Observations Along the Curiosity Rover's Traverse in Gale Crater, Mars

Journal of Geophysical Research Planets (2022)

M. S. Rice Christina Seeger J. F. Bell F. J. Calef Michael St. Clair

Abstract The Mars Science Laboratory Curiosity rover has explored over 400 m of vertical stratigraphy within Gale crater to date. These fluvio‐deltaic, lacustrine, and aeolian strata have been well‐documented by Curiosity's in situ and remote science instruments, including the Mast Camera (Mastcam) pair of multispectral imagers. Mastcam visible to near‐infrared spectra can broadly distinguish between iron phases and oxidation states, and in combination with chemical data from other instruments, Mastcam spectra can help constrain mineralogy, depositional origin, and diagenesis. However, no traverse‐scale analysis of Mastcam multispectral data has yet been performed. We compiled a database of Mastcam spectra from >600 multispectral observations and quantified spectral variations across Curiosity's traverse through Vera Rubin ridge (sols 0–2302). From principal component analysis and an examination of spectral parameters, we identified nine rock spectral classes and five soil spectral classes. Rock classes are dominated by spectral differences attributed to hematite and other oxides (due to variations in grain size, composition, and abundance) and are mostly confined to specific stratigraphic members. Soil classes fall along a mixing line between soil spectra dominated by fine‐grained Fe‐oxides and those dominated by olivine‐bearing sands. By comparing trends in soil versus rock spectra, we find that locally derived sediments are not significantly contributing to the spectra of soils. Rather, varying contributions of dark, mafic sands from the active Bagnold Dune field is the primary spectral characteristic of soils. These spectral classes and their trends with stratigraphy provide a basis for comparison in Curiosity's ongoing exploration of Gale crater.

Spectral slope

10.1029/2021je007134

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Citations (15)

Geologic map of the Glen Torridon region, Gale crater, Mars

Zenodo (CERN European Organization for Nuclear Research) (2022)

Christopher M. Fedo Alex Bryk L. A. Edgar K. A. Bennett V. K. Fox

Geologic map

10.5281/zenodo.7041712

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Datasets for "Synergistic ground and orbital observations of iron oxides on Mt. Sharp and Vera Rubin ridge"

Zenodo (CERN European Organization for Nuclear Research) (2020)

A. A. Fraeman

This repository contains generated datasets used to make figures in "Synergistic ground and orbital observations of iron oxides on Mt. Sharp and Vera Rubin ridge" submitted to the Journal of Geophysical Research: Planets, doi: 10.1029/2019JE006294. This is in accordance with AGU's Data Availability Policy.

10.5281/zenodo.3908551

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The Stratigraphy of Central and Western Butte and the Greenheugh Pediment Contact

A. B. Bryk W. E. Dietrich V. K. Fox K. A. Bennett Steven G. Banham

The Greenheugh pediment at the base of Aeolis Mons (Mt. Sharp), which may truncate units in the Murray formation and is capped by a thin sandstone unit, appears to represent a major shift in climate history within Gale crater. The pediment appears to be an erosional remnant of potentially a much more extensive feature. Curiosity’s traverse through the southern extent of Glen Torridon (south of Vera Rubin ridge) has brought the rover in contact with several new stratigraphic units that lie beneath the pediment. These strata were visited at two outcrop-forming buttes (Central and Western butte- both remnants of the retreating pediment) south of an orbitally defined boundary marking the transition from the Fractured Clay-bearing Unit (fCU) and the fractured Intermediate Unit (fIU). Here we present preliminary interpretations of the stratigraphy within Central and Western buttes and propose the Western butte cap rocks do not match the pediment capping unit.

Butte

Outcrop

Stratigraphic unit

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Citations (2)