Searching for Life on Mars: Selection of Molecular Targets for ESA's Aurora ExoMars Mission

Abstract

The European Space Agency's ExoMars mission will seek evidence of organic compounds of biological and non-biological origin at the martian surface. One of the instruments in the Pasteur payload may be a Life Marker Chip that utilizes an immunoassay approach to detect specific organic molecules or classes of molecules. Therefore, it is necessary to define and prioritize specific molecular targets for antibody development. Target compounds have been selected to represent meteoritic input, fossil organic matter, extant (living, recently dead) organic matter, and contamination. Once organic molecules are detected on Mars, further information is likely to derive from the detailed distribution of compounds rather than from single molecular identification. This will include concentration gradients beneath the surface and gradients from generic to specific compounds. The choice of biomarkers is informed by terrestrial biology but is wide ranging, and nonterrestrial biology may be evident from unexpected molecular distributions. One of the most important requirements is to sample where irradiation and oxidation are minimized, either by drilling or by using naturally excavated exposures. Analyzing regolith samples will allow for the search of both extant and fossil biomarkers, but sequential extraction would be required to optimize the analysis of each of these in turn.

PCR-based analysis of microbial communities during the EuroGeoMars campaign at Mars Desert Research Station, Utah

“…Another advantage would be the integration of a sequencer into this automated process, so that after DNA extraction and PCR amplification with the oligonucleotide primers of choice, the microorganisms could be immediately identified by their sequence. This combination of automated processes will also be highly interesting for unmanned Mars lander missions and could represent a useful additional tool alongside the Life Marker Chip (LMC), one of the key instruments to detect signs of past and present life on Mars during ESA's ExoMars mission on board the ExoMars rover (Parnell et al 2007) or during follow-up missions. In contrast to the PCR-based detection of life, the LMC utilizes immunoassays with a fluorescent readout in a microarray format to detect specific organic molecules or classes of molecules (Parnell et al 2007;Wilson 2007).…”

“…This combination of automated processes will also be highly interesting for unmanned Mars lander missions and could represent a useful additional tool alongside the Life Marker Chip (LMC), one of the key instruments to detect signs of past and present life on Mars during ESA's ExoMars mission on board the ExoMars rover (Parnell et al 2007) or during follow-up missions. In contrast to the PCR-based detection of life, the LMC utilizes immunoassays with a fluorescent readout in a microarray format to detect specific organic molecules or classes of molecules (Parnell et al 2007;Wilson 2007). It would be desirable to develop two independent analytical methods side-by-side to compare, evaluate and confirm the research results.…”

Correlation Between the Extent of Catalytic Activity and Charge Density of Montmorillonites

“…It is our hope, given the demonstrated correlation between the charge density and catalytic activity of montmorillonites, that our results will serve as a kind of ''pathfinder'' for the selection of target sites for future Mars missions in search of organic molecules (Parnell et al, 2007).…”

Searching for Life on Mars: Degradation of Surfactant Solutions Used in Organic Extraction Experiments

“…While the potential for solar heating to generate liquid brines in the shallow subsurface should be noted (Martinez and Renno, 2013, and references therein), the cold, dry environment offered by parts of the martian subsurface is otherwise ideal for the preservation of organic matter. At a depth of about 2 m, the GCR flux has been attenuated sufficiently to favor the survival of organic species over geological timescales (e.g., Kminek and Bada, 2006;Pavlov et al, 2012;Hassler et al, 2014), particularly if the presentday surface has been exposed rather more recently (e.g., Farley et al, 2014), while surface oxidants are expected to be able to penetrate into the regolith to a broadly similar depth (Zent, 1998;Kolb et al, 2002;Parnell et al, 2007). Hope therefore exists that Noachian rocks, deposited in the warmer, wetter climate around 4 Ga (e.g., Carr and Head, 2010), may retain the chemical evidence of martian life.…”