Biosignature Preservation and Detection in Mars Analog Environments

Abstract

This review of material relevant to the Conference on Biosignature Preservation and Detection in Mars Analog Environments summarizes the meeting materials and discussions and is further expanded upon by detailed references to the published literature. From this diverse source material, there is a detailed discussion on the habitability and biosignature preservation potential of five primary analog environments: hydrothermal spring systems, subaqueous environments, subaerial environments, subsurface environments, and iron-rich systems. Within the context of exploring past habitable environments on Mars, challenges common to all of these key environments are laid out, followed by a focused discussion for each environment regarding challenges to orbital and ground-based observations and sample selection. This leads into a short section on how these challenges could influence our strategies and priorities for the astrobiological exploration of Mars. Finally, a listing of urgent needs and future research highlights key elements such as development of instrumentation as well as continued exploration into how Mars may have evolved differently from Earth and what that might mean for biosignature preservation and detection. Key Words: Biosignature preservation-Biosignature detection-Mars analog environments-Conference report-Astrobiological exploration. Astrobiology 17, 363-400.

FIG. 1.

Features that contribute to a habitable environment (Hoehler, 2007).

FIG. 2.

The six types of potential biosignatures identified by the Mars 2020 Science Definition Team (From Mustard et al., 2013).

FIG. 3.

The five types of ancient martian environments that were discussed at the workshop by way of terrestrial analogs (modified from Des Marais et al., 2008a).

FIG. 4.

The ca. 3.4 Ga Dresser Formation is an example of an ancient hydrothermal spring system and its potential biosignatures in the Pilbara Craton, Western Australia. In this schematic cross section, geothermal heat flow and circulating water are indicated by the red and blue arrows, respectively. The chemical sediments, indicated as blue irregular shapes in the figure, include fabrics consistent with geyserite and the former presence of microbial communities (Djokic, ; Djokic et al., unpublished data).

FIG. 5.

Examples of potential biosignatures in hydrothermal spring deposits: palisade textures in terracettes sinter fabrics (Djokic et al., 2017).

FIG. 6.

(a) Schematic cross section of a delta system grading into a lacustrine setting. Blue arrow indicates prograding fining upward sequence of prodelta deposits. (b) An aerial view of the Saskatchewan River delta flowing into a large catchment with onshore embayments as well as visible supra- and subaerial alluvial fans [(a) and (b) credit: NASA/JPL/Imperial College]. (c) A similar system exposed in the Aeolis/Zephyria Plana region of Mars (from Burr et al., 2009).

FIG. 7.

(a) Opaque filamentous structures associated with 0.05–0.1 wt % organic carbon in a 2.76 Ga basaltic paleosol in the Pilbara Craton (modified from Rye and Holland, 2000). (b) Organic carbon in the carbonate-rich 2.6–2.7 Ga Kaapvaal Craton paleosol, part of a unit interpreted as a surface layer containing 0.1–0.36 wt % organic carbon (modified from Watanabe et al., 2000). Both (a) and (b) are interpreted to be organic matter from surface microbial mats. (c) Example of a paleosol sequence, John Day Fossil Beds National Monument, Oregon (credit: B. Horgan). (d) Modern microbialites compared to layered textures consistent with microbialites in 100 ka and Jurassic spring deposits. (e) Modern circumneutral cold spring supporting surface microbial communities near Green River, Utah, compared to outcrop of Jurassic cold spring deposits in the Brushy Basin Member of the Morrison Formation, Colorado ((d) and (e) modified from Potter-McIntyre et al., 2016).

FIG. 8.

Cave skylight on the flank of Pavonis Mons in the Tharsis Region taken by the HiRISE camera on the Mars Reconnaissance Orbiter. Cave entrance is estimated to be 180 m wide. Credit: NASA/JPL/University of Arizona.

FIG. 9.

(a) Example of iron-rich environment on Mars: Hematite Ridge in Gale Crater. Image Credit: NASA/JPL-Caltech/Univ. of Arizona. (b) Biofabric composed of masses of filamentous microbes encrusted by iron oxides from acid mine drainage at Iron Mountain, California (Williams et al., 2016). (c) Jurassic iron and carbonate biofabric from a spring deposit in the Brushy Basin Member of the Morrison Formation. These delicate macroscopic terracette features have undergone 150 million years of diagenetic alteration yet are still recognizable in outcrop (Potter-McIntyre et al., 2016). (d) Iron-encrusted filamentous microbe from Iron Mountain (Williams et al., 2016). (e) Transmission electron microscope image of iron-mineralized spiral stalk from Mariprofundus ferrooxydans (scale bar = 1 μm; Chan et al., 2011). (f) Lipid biomarkers (midchain mono- and dimethylalkanes) isolated from modern and subrecent iron-mineralized microbial mats (Parenteau et al., 2014, 2016).