UVolution, a Photochemistry Experiment in Low Earth Orbit: Investigation of the Photostability of Carboxylic Acids Exposed to Mars Surface UV Radiation Conditions Fabien Stalport, 1,2 Yuan Yong Guan, 1 Patrice Coll, 1 Cyril Szopa, 3 Fre ´ de ´ rique Macari, 1 Franc ¸ ois Raulin, 1 Didier Chaput, 4 and Herve ´ Cottin 1 Abstract The detection and identification of organic molecules on Mars are of prime importance to establish the existence of a possible ancient prebiotic chemistry or even a biological activity. To date, however, no complex organic compounds have been detected on Mars. The harsh environmental conditions at the surface of Mars are com- monly advocated to explain this nondetection, but few studies have been implemented to test this hypothesis. To investigate the nature, abundance, and stability of organic molecules that could survive under such environ- mental conditions, we exposed, in low Earth orbit, organic molecules of martian astrobiological relevance to solar UV radiation (>200 nm). The experiment, called UVolution, was flown on board the Biopan ESA module, which was situated outside a Russian Foton automated capsule and exposed to space conditions for 12 days in September 2007. The targeted organic molecules [a-aminoisobutyric acid (AIB), mellitic acid, phthalic acid, and trimesic acid] were exposed with, and without, an analogous martian soil. Here, we present experimental results of the impact of solar UV radiation on the targeted molecules. Our results show that none of the organic molecules studied seemed to be radiotolerant to the solar UV radiation when directly exposed to it. Moreover, the presence of a mineral matrix seemed to increase the photodestruction rate. AIB, mellitic acid, phthalic acid, and trimesic acid should not be considered as primary targets for in situ molecular analyses during future surface missions if samples are only collected from the first centimeters of the top surface layer. Key Words: Space mission—Mars—Astrobiology—UV radiation—Organic matter. Astrobiology 10, 449–461. 1. Introduction M ars is a primary target of astrobiological interest: its past environmental conditions may have been favor- able to the emergence of a prebiotic chemistry and, possibly, biological activity. Since 2004, several space missions (Mars Exploration Rovers, Mars Express, Phoenix, and Mars Re- connaissance Orbiter) have provided data that suggest liquid water, an essential ingredient for life as we know it, was present on Mars throughout its first 500 million years of existence (Squyres et al., 2004; Bibring et al., 2006). In situ exploration is currently underway at the surface of Mars, and specific studies have been implemented to determine whether life is, or has been, present. In this context, the detection of organic molecules is of critical importance in that they are known to be among the best biosignatures, that is, indicators of past or present biological activity. To date, the only hy- drocarbon tentatively detected on Mars is methane, which, according to recent studies, occurs at an extremely low con- centration (Formisano et al., 2004; Krasnopolsky et al., 2004). The presence of methane on Mars can be attributed to biotic or abiotic processes. More-complex organic material, which would be a signature of a prebiotic chemistry or even a bio- logical activity, typically has lower volatilities and may be present in the regolith where its detection requires in situ measurements at the Mars surface. To date, the only in situ space experiment devoted to the detection of organic molecules has been the gas 1 Laboratoire Interuniversitaire des Syste `mes Atmosphe ´riques (LISA), UMR 7583 CNRS, Universities of Paris 7 and Paris 12, Cre ´teil, France. 2 NASA Goddard Space Flight Center (GSFC), Greenbelt, Maryland. 3 UPMC University of Paris 6; Universite ´ Versailles St-Quentin; CNRS=INSU, LATMOS-IPSL, Paris, France. 4 Centre National d’Etudes Spatiales, Toulouse, France. ASTROBIOLOGY Volume 10, Number 4, 2010 ª Mary Ann Liebert, Inc. DOI: 10.1089=ast.2009.0413 449