The search for a signature of life on Mars: a biogeomorphological approach
Résumé
Geological evidence shows that life on Earth evolved in line with major concomitant changes in Earth surface processes and landforms. Biogeomorphological characteristics, especially those involving microorganisms, are potentially important facets of biosignatures on Mars and are generating increasing interest in Astrobiology. Using Earth as an analog provides reasons to suspect that past or present life on Mars could have resulted in recognizable biogenic landforms. Here, we discuss the potential and limitations of a biogeomorphological approach in identifying the subsets of landforms modulated or created through biological processes, and thus presenting signatures of life on Mars. Subsets especially involving microorganisms that are potentially important facets of biosignatures on Mars are proposed: (i) weathering figures, biocrusts, patinas and varnishes; (ii) microbialites and microbially induced sedimentary structures (MISS); (iii) bioaccumulations of skeletal remains; (iv) degassing landforms; (v) cryoconites; (vi) self-organized patterns; (vii) unclassified non-analog landforms. We propose a biogeomorphological frequency histogram approach to identify anomalies/modulations in landform properties. Such detection of anomalies/modulations will help to track a biotic origin and lead to the development of an integrative multi-proxy and multi-scale approach combining morphological, structural, textural and geochemical expertise. This perspective can help to guide the choice of investigation sites for future missions and the types and scales of observations to be made by orbiters and rovers.