UVolution, a Photochemistry Experiment in Low Earth Orbit: Investigation of the Photostability of Carboxylic Acids Exposed to Mars Surface UV Radiation Conditions

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 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 [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.

Earth as a Tool for Astrobiology—A European Perspective

“…Initially, these experiments were focused on the impact of UV radiation and oxidation processes. Table 1 highlights some key parameters of some laboratory simulations submitting pure or mixed organic molecules to simulated Martian UV sources (Hintze et al 2010;Johnson and Pratt 2010;Oro and Holzer 1979;Poch et al 2013Poch et al , 2014Poch et al , 2015Schuerger et al 2008;Stalport et al 2008Stalport et al , 2009Stalport et al , 2010Stoker and Bullock 1997;ten Kate et al 2005ten Kate et al , 2006. Among these parameters, the use of a Xenon arc lamp as the radiation source has proven to better reproduce the energy and relative abundance of the UV photons (190 to 400 nm) supposed to reach the surface of Mars (Schuerger et al 2003).…”

The PROCESS Experiment: Amino and Carboxylic Acids Under Mars-Like Surface UV Radiation Conditions in Low-Earth Orbit

“…Indeed, the interplanetary medium is still an active exogenous source of organic matter (Cottin et al, 1999;Botta and Bada, 2002;Elsila et al, 2009;SchmittKopplin et al, 2010), and if follows that this exogenous organic matter should have been detected by the Viking instruments. Today, two main hypotheses attempt to explain the Viking results: (i) the gas chromatograph-mass spectrometer (GC-MS) instrument would not have been ideally suited to detect low levels of organics in the samples collected by Viking (Navarro-González et al, 2006 and (ii) organics were effectively absent from the samples collected because of chemical processes that occur at the surface of the planet and lead to the degradation of these molecules (Stoker and Bullock, 1997;Benner et al, 2000;Ten Kate et al, 2006;Stalport et al, 2009Stalport et al, , 2010a. Furthermore, it is also important to note that the Viking landers sampled martian soils from two very localized locations.…”

“…On board these two space probes instruments such as Sample Analysis at Mars (SAM) have the capacity to detect very low levels of organics (Cabane et al, 2004). Also, a new set of laboratory studies, developed within the Mars Organic Molecules Irradiation and Evolution (MOMIE) program, that support these ambitious space programs is devoted to evaluation of the behavior of organic compounds under simulated martian surface environmental conditions (Stalport et al, , 2009(Stalport et al, , 2010a. The major goals of these studies are (i) the identification of the nature of organic molecules that could be stable or metastable at the surface of Mars, (ii) the assessment of the ability to detect them by in situ instrumentation, and (iii) the quantification of their abundance at the surface of the planet.…”

“…This work has been initiated with the UVolution experiment. This experiment was contained in an ESA Biopan facility outside a Foton automated capsule in 2007 (Guan et al, 2010;Stalport et al, 2010aStalport et al, , 2010b (ESA and CNES). The PROCESS samples consist of a set of organic compounds related to cometary or martian environments.…”

Space as a Tool for Astrobiology: Review and Recommendations for Experimentations in Earth Orbit and Beyond

“…The case of Martian simulations is more favorable since the lamps simulating the UV flux reaching the surface of Mars (λ > 190 nm) are quite acceptable sources. However, there is still a factor of 2 to 13 difference between space and laboratory results, depending on the molecule remains (Stalport et al 2010a). Interestingly, UVolution results have shown that, contrary to previous measurements of shielding effects due to organic compounds embedded in minerals, photolysis of organic molecules can be activated by the presence of a mineral analogue of Martian soil.…”