The Significance of Microbe-Mineral-Biomarker Interactions in the Detection of Life on Mars and Beyond

Abstract

The detection of biomarkers plays a central role in our effort to establish whether there is, or was, life beyond Earth. In this review, we address the importance of considering mineralogy in relation to the selection of locations and biomarker detection methodologies with characteristics most promising for exploration. We review relevant mineral-biomarker and mineral-microbe interactions. The local mineralogy on a particular planet reflects its past and current environmental conditions and allows a habitability assessment by comparison with life under extreme conditions on Earth. The type of mineral significantly influences the potential abundances and types of biomarkers and microorganisms containing these biomarkers. The strong adsorptive power of some minerals aids in the preservation of biomarkers and may have been important in the origin of life. On the other hand, this strong adsorption as well as oxidizing properties of minerals can interfere with efficient extraction and detection of biomarkers. Differences in mechanisms of adsorption and in properties of minerals and biomarkers suggest that it will be difficult to design a single extraction procedure for a wide range of biomarkers. While on Mars samples can be used for direct detection of biomarkers such as nucleic acids, amino acids, and lipids, on other planetary bodies remote spectrometric detection of biosignatures has to be relied upon. The interpretation of spectral signatures of photosynthesis can also be affected by local mineralogy. We identify current gaps in our knowledge and indicate how they may be filled to improve the chances of detecting biomarkers on Mars and beyond.

Quantifying bioalbedo: a new physically based model and discussion of empirical methods for characterising biological influence on ice and snow albedo

“…4c) that is commonly used to remotely de-tect terrestrial vegetation and ocean plankton blooms (e.g. Roling et al, 2015;Joint and Groom, 2000). Therefore, the red-edge biomarker can only be used to remotely sense ice algae if dust can be accurately accounted for; otherwise there is a high risk of a biomarker false positive.…”

“…Wientjes et al, 2011) and the similarity of spectral signatures resulting from biotic and abiotic impurities make abiotic impurities a crucial component of bioalbedo investigations, especially those aiming to detect biological impurities remotely or quantifying biological albedo reduction empirically. The reflectance of some minerals is difficult to distinguish from that of microbes (Seager et al, 2005) and interactions of microbes with minerals can obscure or modify biological reflectance spectra (Roling et al, 2015). Therefore, if a chlorophyll-or carotenoid-based biomarker is designed to be universally applicable (e.g.…”

A short comment

“…For an isotropically scattering (Lambertian) surface, incoming solar radiation is scattered equally in all directions in the overlying hemisphere such that reflected radiance in any one direction is equal to that in all other directions. However, all natural surfaces exhibit some degree of anisotropy (Schaepman-Strub et al, 2006). Snow and ice preferentially scatter light in the forward direction, although the angular distribution depends on lighting geometry, ice optical properties, surface roughness and wavelength (Aoki et al, 2000;Dumont et al, 2010;Hudson et al, 2006).…”

“…Technically, the BRDF is also a conceptual quantity, because it is defined by infinitesimal illumination and viewing angles. However, the BRDF can be well approximated using measurements or simulations at fine angular resolution (Schaepman-Strub et al, 2006), although this is difficult under natural illumination, because even in clear-sky conditions a large fraction of the UV and blue light is diffuse. Snow and ice albedo is also sensitive to the direction of incoming solar irradiance.…”

“…4.10). In this case, the spectral distribution of incoming solar irradiance is best measured using a white reference panel (Schaepman-Strub et al, 2006;McCoy, 2005;Milton et al, 2009). Because the panel is as close as possible to an isotropic scattering surface, light reflected from it approximates the spectral characteristics of incoming solar irradiance.…”