Dimerization of Uracil in a Simulated Mars-like UV Radiation Environment.

The search for organic molecules at the surface of Mars is a key objective in astrobiology, given that many organic compounds are possible biosignatures and their presence is of interest with regard to the habitability of Mars. Current environmental conditions at the martian surface are harsh and affect the stability of organic molecules. For this reason, and because current and future Mars rovers collect samples from the upper surface layer, it is important to assess the fate of organic molecules under the conditions at the martian surface. Here, we present an experimental study of the evolution of uracil when exposed to UV radiation, pressure, and temperature conditions representative of the surface of Mars. Uracil was selected because it is a nucleobase that composes RNA, and it has been detected in interplanetary bodies that could be the exogenous source of this molecule by meteoritic delivery to the surface of Mars. Our results show that the experimental quantum efficiency of photodecomposition of uracil is 0.16 ± 0.14 molecule/photon. Although these results suggest that uracil is quickly photodegraded when directly exposed to UV light on Mars, such exposure produces dimers that are more stable over time than the monomer. The identified dimers could be targets of interest for current and future Mars space missions.

High-resolution mass spectrometry for future space missions: Comparative analysis of complex organic matter with LAb-CosmOrbitrap and laser desorption/ionization Fourier transform ion cyclotron resonance.

RATIONALE: Mass spectrometers are regularly boarded on spacecraft for the exploration of the Solar System. A better understanding of the origin, distribution and evolution of organic matter and its relationships with inorganic matter in different extra-terrestrial environments requires the development of innovative space tools, described as Ultra-High-Resolution Mass Spectrometry (UHRMS) instruments. METHODS: Analyses of a complex organic material simulating extraterrestrial matter (Titan's tholins) are performed with a homemade space-designed Orbitrap™ equipped with a laser ablation ionization source at 266 nm: the LAb-CosmOrbitrap. Mass spectra are obtained using only one laser shot and transient duration of 838 ms. A comparison is made on the same sample with a laboratory benchmark mass spectrometer: a Fourier Transform Ion Cyclotron Resonance equipped with a laser desorption ionization source at 355 nm (LDI-FTICR) allowing accumulation of 20,000 laser shots. RESULTS: Mass spectra and attributions of molecular formulae based on the peaks detected by both techniques show significant similarities. Detection and identification of the same species are validated. The formation of clusters ions with the LAb-CosmOrbitrap is also presented. This specific feature brings informative and unusual indirect detections about the chemical compounds constituting Titan's tholins. In particular, the detection of HCN confirms previous results obtained with laboratory Electrospray Ionization (ESI)-UHRMS studies about the understanding of polymeric patterns for the formation of tholins. CONCLUSIONS: The capabilities of the LAb-CosmOrbitrap to decipher complex organic mixtures using single laser shot and a short transient are highlighted. In agreement with results provided by a commercial FTICR instrument in the laboratory, we demonstrate in this work the relevance of a space laser-CosmOrbitrap instrument for future planetary exploration.

An Orbitrap-based laser desorption/ablation mass spectrometer designed for spaceflight.

RATIONALE: The investigation of cryogenic planetary environments as potential harbors for extant life and/or contemporary sites of organic synthesis represents an emerging focal point in planetary exploration. Next generation instruments need to be capable of unambiguously determining elemental and/or molecular stoichiometry via highly accurate mass measurements and the separation of isobaric interferences. METHODS: An Orbitrap™ analyzer adapted for spaceflight (referred to as the CosmOrbitrap), coupled with a commercial pulsed UV laser source (266 nm), was used to successfully characterize a variety of planetary analog samples via ultrahigh resolution laser desorption/ablation mass spectrometry. The materials analyzed in this study include: jarosite (a hydrous sulfate detected on Mars); magnesium sulfate (a potential component of the subsurface ocean on Europa); uracil (a nucleobase of RNA); and a variety of amino acids. RESULTS: The instrument configuration tested here enables: measurement of major elements and organic molecules with ultrahigh mass resolution (m/Δm ≥ 120,000, FWHM); quantification of isotopic abundances with <1.0% (2σ) precision; and identification of highly accurate masses within 3.2 ppm of absolute values. The analysis of a residue of a dilute solution of amino acids demonstrates the capacity to detect twelve amino acids in positive ion mode at concentrations as low as ≤1 pmol/mm2 while maintaining mass resolution and accuracy requirements. CONCLUSIONS: The CosmOrbitrap mass analyzer is highly sensitive and delivers mass resolution/accuracy unmatched by any instrument sent into orbit or launched into deep space. This prototype instrument, which maps to a spaceflight implementation, represents a mission-enabling technology capable of advancing planetary exploration for decades to come.