Organic degradation under simulated Martian conditions

Abstract

Abstract. We report on laboratory experiments which simulate the breakdown of organic compounds under Martian surface conditions. Chambers containing Mars-analog soil mixed with the amino acid glycine were evacuated and filled to 100 mbar pressure with a Martian atmosphere gas mixture and then irradiated with a broad spectrum Xe lamp. Headspace gases were periodically withdrawn and analyzed via gas chromatography for the presence of organic gases expected to be decomposition products of the glycine. The quantum efficiency for the decomposition of glycine by light at wavelengths from 2000 to 2400 A was measured to be 1.46 + 1.0 x 10 -6 molecules/photon. Scaled to Mars, this represents an organic destruction rate of 2.24 _+ 1.2 x 10 -4 g of C m -2 yr-1. We compare this degradation rate with the rate that organic compounds are brought to Mars as a result of meteoritic infall to show that organic compounds are destroyed on Mars at rates far exceeding the rate that they are deposited by meteorites. Thus the fact that no organic compounds were found on Mars by the Viking Lander Gas Chromatograph Mass Spectrometer experiment can be explained without invoking the presence of strong oxidants in the surface soils. The organic destruction rate may be considered as an upper bound for the globally averaged biomass production rate of extant organisms at the surface of Mars. This upper bound is comparable to the slow growing cryptoendolithic microbial communities found in dry Antarctica deserts. Finally, comparing these organic destruction rates to recently reported experiments on the stability of carbonate on the surface of Mars, we t'ind that organic compounds may currently be more stable than calcite.

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).…”

Gale crater: the Mars Science Laboratory/Curiosity Rover Landing Site

“…Steele et al 2012) at the Martian surface include Solar ultraviolet radiation (e.g. Stoker & Bullock 1997) and oxidizing compounds (e.g. Benner et al 2000).…”

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

“…The harsh martian environment could also explain the lack of organics if conditions are such that they are destroyed. In this context, several experimental and numerical modeling studies were performed to evaluate the possibility for the destruction and=or evolution of the organics under martian surface environmental conditions (Oro and Holzer, 1979;Stoker and Bullock, 1997;ten Kate et al, 2005ten Kate et al, , 2006Stalport et al, 2008Stalport et al, , 2009. Solar UV radiation is a major source of energy that can initiate chemical evolution of organics and has been proposed as an explanation for the lack of organics at the surface of Mars.…”