The PROCESS experiment: an astrochemistry laboratory for solid and gaseous organic samples in low-earth orbit.

The PROCESS (PRebiotic Organic ChEmistry on the Space Station) experiment was part of the EXPOSE-E payload outside the European Columbus module of the International Space Station from February 2008 to August 2009. During this interval, organic samples were exposed to space conditions to simulate their evolution in various astrophysical environments. The samples used represent organic species related to the evolution of organic matter on the small bodies of the Solar System (carbonaceous asteroids and comets), the photolysis of methane in the atmosphere of Titan, and the search for organic matter at the surface of Mars. This paper describes the hardware developed for this experiment as well as the results for the glycine solid-phase samples and the gas-phase samples that were used with regard to the atmosphere of Titan. Lessons learned from this experiment are also presented for future low-Earth orbit astrochemistry investigations.

The PROCESS experiment: amino and carboxylic acids under Mars-like surface UV radiation conditions in low-earth orbit.

The search for organic molecules at the surface of Mars is a top priority of the next Mars exploration space missions: Mars Science Laboratory (NASA) and ExoMars (ESA). The detection of organic matter could provide information about the presence of a prebiotic chemistry or even biological activity on this planet. Therefore, a key step in interpretation of future data collected by these missions is to understand the preservation of organic matter in the martian environment. Several laboratory experiments have been devoted to quantifying and qualifying the evolution of organic molecules under simulated environmental conditions of Mars. However, these laboratory simulations are limited, and one major constraint is the reproduction of the UV spectrum that reaches the surface of Mars. As part of the PROCESS experiment of the European EXPOSE-E mission on board the International Space Station, a study was performed on the photodegradation of organics under filtered extraterrestrial solar electromagnetic radiation that mimics Mars-like surface UV radiation conditions. Glycine, serine, phthalic acid, phthalic acid in the presence of a mineral phase, and mellitic acid were exposed to these conditions for 1.5 years, and their evolution was determined by Fourier transform infrared spectroscopy after their retrieval. The results were compared with data from laboratory experiments. A 1.5-year exposure to Mars-like surface UV radiation conditions in space resulted in complete degradation of the organic compounds. Half-lives between 50 and 150 h for martian surface conditions were calculated from both laboratory and low-Earth orbit experiments. The results highlight that none of those organics are stable under low-Earth orbit solar UV radiation conditions.

UVolution, a photochemistry experiment in low earth orbit: investigation of the photostability of carboxylic acids exposed to mars surface UV radiation conditions.

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 commonly 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 environmental 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 [alpha-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.