Potential for irradiation of methane to form complex organic molecules in impact craters: Implications for Mars, Titan and Europa John Parnell ⁎ , Martin Baron, Paula Lindgren Department of Geology and Petroleum Geology, University of Aberdeen, Aberdeen AB24 3UE, UK Received 16 August 2005; accepted 7 November 2005 Available online 24 March 2006 Abstract The release of methane from crater sites following meteorite impact is a possible consequence of the thermal alteration of organic matter, or tapping of reservoired gas of biogenic or abiogenic origin. At least the latter is feasible on Mars. Methane and higher hydrocarbons are susceptible to polymerization and precipitation by radioactive minerals. Where such minerals are present in impact target rocks, the craters can be a preferred site for carbon concentration, and the formation of complex organic molecules. On icy bodies, such as Titan and Europa, methane released by impact could be a fuel for prebiotic chemistry involving other forms of irradiation. © 2006 Elsevier B.V. All rights reserved. Keywords: Methane; Irradiation; Mars; Europa 1. Introduction The occurrence of methane on Mars (Formisano et al., 2004) and Titan (Barth and Toon, 2004) emphasizes the possibility that these solar system bodies could have supported prebiotic chemistry. Methane can be of abiogenic or biogenic origin. If there is any buried organic matter on Mars, methane may be generated due to the thermal effect of impacts which would yield methane into subsequent hydrothermal systems (Oehler et al., 2005). We discuss here the potential for the irradiation of methane to complex organic molecules by radioactive minerals in impact craters. 2. Methane release from impact craters The fluid inclusion record in terrestrial craters shows that fluids are predominantly aqueous (Parnell et al., 2006). However, traces of methane have been recorded in a few craters, such as in the impact-related Sudbury Igneous Complex (Hanley et al., 2005), and the Lockne and Gardnos craters in the Scandinavian Caledonides. At Lockne, Sweden, methane is interpreted to have been formed from organic-rich sediment by impact-related hydrothermal heating (Sturkell et al., 1998), while at Gardnos, Norway, the methane is attributed to later metamorphism of impact-generated hydrocarbons (Andersen and Burke, 1996). The ambient conditions of methane entrapment are constrained by the density of methane inclusions, inferred from their homogenization temperatures. Journal of Geochemical Exploration 89 (2006) 322 – 325 www.elsevier.com/locate/jgeoexp ⁎ Corresponding author. E-mail address: j.parnell@abdn.ac.uk (J. Parnell). 0375-6742/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.gexplo.2005.11.024