Preservation of Martian Organic and Environmental Records: Final Report of the Mars Biosignature Working Group

Abstract

International audienceThe Mars Science Laboratory (MSL) has an instrument package capable of making measurements of past and present environmental conditions. The data generated may tell us if Mars is, or ever was, able to support life. However, the knowledge of Mars' past history and the geological processes most likely to preserve a record of that history remain sparse and, in some instances, ambiguous. Physical, chemical, and geological processes relevant to biosignature preservation on Earth, especially under conditions early in its history when microbial life predominated, are also imperfectly known. Here, we present the report of a working group chartered by the Co-Chairs of NASA's MSL Project Science Group, John P. Grotzinger and Michael A. Meyer, to review and evaluate potential for biosignature formation and preservation on Mars. Orbital images confirm that layered rocks achieved kilometer-scale thicknesses in some regions of ancient Mars. Clearly, interplays of sedimentation and erosional processes govern present-day exposures, and our understanding of these processes is incomplete. MSL can document and evaluate patterns of stratigraphic development as well as the sources of layered materials and their subsequent diagenesis. It can also document other potential biosignature repositories such as hydrothermal environments. These capabilities offer an unprecedented opportunity to decipher key aspects of the environmental evolution of Mars' early surface and aspects of the diagenetic processes that have operated since that time. Considering the MSL instrument payload package, we identified the following classes of biosignatures as within the MSL detection window: organism morphologies (cells, body fossils, casts), biofabrics (including microbial mats), diagnostic organic molecules, isotopic signatures, evidence of biomineralization and bioalteration, spatial patterns in chemistry, and biogenic gases. Of these, biogenic organic molecules and biogenic atmospheric gases are considered the most definitive and most readily detectable by MSL

Curiosity’s Mars Hand Lens Imager (MAHLI) Investigation

“…MAHLI images could certainly resolve macroscopic groupings of micro-organisms (e.g., patches of crustose lichen on a rock) if they occur, but no such features have been found in MER MI or Phoenix Robotic Arm Camera (RAC) images already acquired on Mars. In order to be readily resolved by MAHLI, biosignatures, such as body fossils or evidence of sediment bioturbation, would have to occur at a scales > 100 µm (Summons et al 2011). Certain biofabrics-such as microbial laminae and composite microbial structures (e.g.…”

“…Certain biofabrics-such as microbial laminae and composite microbial structures (e.g. stromatolites)-would certainly be detectable (Summons et al 2011;Williams and Sumner 2012), although these are not without controversy, as abiogenic structures can mimic biofabric (e.g., McLoughlin et al 2008).…”

MAHLI on Mars: lessons learned operating a geoscience camera on a landed payload robotic arm

“…More typically for Mars, where differences between materials are more subtle, MAHLI images can permit distinction of very fine sand from silt (silt grain sizes as defined by Wentworth, 1922, > 62.5 µm diameter) from unresolvable coarse silt-sized or smaller. This is particularly important to the MSL goal of detecting environments that may once have been habitable (Grotzinger et al, 2012), as mudstone is a great preserver of biosignatures (e.g., Summons et al, 2011).…”

The persistence of a chlorophyll spectral biosignature from Martian evaporite and spring analogues under Mars-like conditions

“…It is unlikely that there is near-surface extant life presently on Mars due to high levels of ultraviolet (UV) irradiation, low temperatures and pressures, as well as oxidative and desiccating conditions (Kminek & Bada 2006;Dartnell et al 2007;Johnson et al 2011;Gómez et al 2012), however, in its history it may have possessed more habitable conditions (Farmer & Des Marais 1999;Cockell et al 2000;Summons et al 2011). The Noachian era of Mars' history was warmer and wetter than present day, as evidenced by accumulations of phyllosilicates, carbonates and sulphates (Squyres et al 2004(Squyres et al , 2012Gendrin et al 2005;Mustard et al 2008;Murchie et al 2009;Rice et al 2010;Elhmann & Mustard 2012), implying the past presence of water, which is essential to carbon-based life as it is currently understood.…”

“…Proposed environments for the last vestiges of life on Mars include Noachian evaporite and spring deposits (Rothschild 1990;Grasby et al 2003;Manicelli et al 2004;Grasby & Londry 2007;Summons et al 2011). Both types of deposits imply the presence of saline waters that may have been present on or near the surface for extended periods of time.…”