Habitability on Early Mars and the Search for Biosignatures with the ExoMars Rover

The second ExoMars mission will be launched in 2020 to target an ancient location interpreted to have strong potential for past habitability and for preserving physical and chemical biosignatures (as well as abiotic/prebiotic organics). The mission will deliver a lander with instruments for atmospheric and geophysical investigations and a rover tasked with searching for signs of extinct life. The ExoMars rover will be equipped with a drill to collect material from outcrops and at depth down to 2 m. This subsurface sampling capability will provide the best chance yet to gain access to chemical biosignatures. Using the powerful Pasteur payload instruments, the ExoMars science team will conduct a holistic search for traces of life and seek corroborating geological context information. Key Words: Biosignatures—ExoMars—Landing sites—Mars rover—Search for life. Astrobiology 17, 471–510. Table of Contents 1. Article Organization 2. Introduction 2.1. ExoMars origin 2.2. A difficult adolescence 2.3. Joint program 3. Early Mars as an Exobiology Target 3.1. A first window of opportunity for life 3.2. Separate ways 3.2.1. Young Earth 3.2.2. Young Mars 3.2.3. Young Venus 3.3. Lessons for ExoMars: when and where? 4. Biosignatures: Which and How Reliable? 4.1. Morphological biosignatures 4.2. Chemical biosignatures 4.2.1. Isomerism selectivity 4.2.2. Molecular weight fingerprints 4.2.3. Bulk isotopic fractionation 4.3. Importance of geological context for boosting biosignature confidence 4.4. Life’s decision points 4.5. Examples using the ExoMars biosignature score 4.5.1. Kitty’s Gap, N.W. Australia 4.5.2. Josefsdal Chert, Barberton, South Africa 4.5.3. Martian Meteorite ALH84001 4.5.4. Yellowknife Bay, Mars 5. The Martian Environment and the Need for Subsurface Exploration 5.1. Results from previous missions 5.2. Degradation of organic matter 5.3. Access to molecular biosignatures 6. The ExoMars Rover and Its Pasteur Payload 6.1. From panoramic to molecular scale through nested investigations 6.2. Pasteur payload instruments 6.2.1. Panoramic camera system 6.2.2. IR spectrometer 6.2.3. Shallow ground-penetrating radar 6.2.4. Subsurface neutron detector 6.2.5. Close-up imager 6.2.6. Drill IR spectrometer 6.2.7. Subsurface drill 6.2.8. Sample preparation and distribution system 6.2.9. MicrOmega 6.2.10. Raman laser spectrometer 6.2.11. Mars organic molecule analyzer 6.3. The reference surface mission 7. A Suitable Landing Site 7.1. Scientific constraints 7.2. Engineering constraints 7.3. Planetary protection constraints 7.4. Possible locations for landing 7.4.1. Oxia Planum (18.159°N, 335.666°E; −3 km MOLA) 7.4.2. Mawrth Vallis (22.160°N, 342.050°E; −2 km MOLA) 8. Conclusions Acknowledgments Author Disclosure Statement References Abbreviations Used