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Astrobiology

Title:		Prebiotic Chemistry of Pluto
Author(s):		Cruikshank DP; Materese CK; Pendleton YJ; Boston PJ; Grundy WM; Schmitt B; Lisse CM; Runyon KD; Keane JT; Beyer RA; Summers ME; Scipioni F; Stern SA; Dalle Ore CM; Olkin CB; Young LA; Ennico K; Weaver HA; Bray VJ;
Address:		"1NASA Ames Research Center, Moffett Field, California, USA. 2Goddard Space Flight Center, Greenbelt, Maryland, USA. 3Lowell Observatory, Flagstaff, Arizona, USA. 4Universite Grenoble Alpes, CNRS, IPAG, Grenoble, France. 5Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA. 6California Institute of Technology, Pasadena, California, USA. 7Department of Physics and Astronomy, George Mason University, Fairfax, Virginia, USA. 8Southwest Research Institute, Boulder, Colorado, USA. 9Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA"
Journal Title:		Astrobiology
Year:		2019
Volume:		20190323
Issue:		7
Page Number:		831 - 848
DOI:		10.1089/ast.2018.1927
ISSN/ISBN:		1557-8070 (Electronic) 1557-8070 (Linking)
Abstract:		"We present the case for the presence of complex organic molecules, such as amino acids and nucleobases, formed by abiotic processes on the surface and in near-subsurface regions of Pluto. Pluto's surface is tinted with a range of non-ice substances with colors ranging from light yellow to red to dark brown; the colors match those of laboratory organic residues called tholins. Tholins are broadly characterized as complex, macromolecular organic solids consisting of a network of aromatic structures connected by aliphatic bridging units (e.g., Imanaka et al., 2004; Materese et al., 2014, 2015). The synthesis of tholins in planetary atmospheres and in surface ices has been explored in numerous laboratory experiments, and both gas- and solid-phase varieties are found on Pluto. A third variety of tholins, exposed at a site of tectonic surface fracturing called Virgil Fossae, appears to have come from a reservoir in the subsurface. Eruptions of tholin-laden liquid H(2)O from a subsurface aqueous repository appear to have covered portions of Virgil Fossae and its surroundings with a uniquely colored deposit (D.P. Cruikshank, personal communication) that is geographically correlated with an exposure of H(2)O ice that includes spectroscopically detected NH(3) (C.M. Dalle Ore, personal communication). The subsurface organic material could have been derived from presolar or solar nebula processes, or might have formed in situ. Photolysis and radiolysis of a mixture of ices relevant to Pluto's surface composition (N(2), CH(4), CO) have produced strongly colored, complex organics with a significant aromatic content having a high degree of nitrogen substitution similar to the aromatic heterocycles pyrimidine and purine (Materese et al., 2014, 2015; Cruikshank et al., 2016). Experiments with pyrimidines and purines frozen in H(2)O-NH(3) ice resulted in the formation of numerous nucleobases, including the biologically relevant guanine, cytosine, adenine, uracil, and thymine (Materese et al., 2017). The red material associated with the H(2)O ice may contain nucleobases resulting from energetic processing on Pluto's surface or in the interior. Some other Kuiper Belt objects also exhibit red colors similar to those found on Pluto and may therefore carry similar inventories of complex organic materials. The widespread and ubiquitous nature of similarly complex organic materials observed in a variety of astronomical settings drives the need for additional laboratory and modeling efforts to explain the origin and evolution of organic molecules. Pluto observations reveal complex organics on a small body that remains close to its place of origin in the outermost regions of the Solar System"
Keywords:		"Atmosphere/*analysis/chemistry Extraterrestrial Environment/*chemistry Ice Methane/analysis *Pluto Purines/*analysis Pyrimidines/*analysis Spectrophotometry, Infrared Volatile Organic Compounds/analysis Water/chemistry Nucleobase Pluto Tholin;"
Notes:		"MedlineCruikshank, D P Materese, C K Pendleton, Y J Boston, P J Grundy, W M Schmitt, B Lisse, C M Runyon, K D Keane, J T Beyer, R A Summers, M E Scipioni, F Stern, S A Dalle Ore, C M Olkin, C B Young, L A Ennico, K Weaver, H A Bray, V J eng Research Support, U.S. Gov't, Non-P.H.S. 2019/03/26 Astrobiology. 2019 Jul; 19(7):831-848. doi: 10.1089/ast.2018.1927. Epub 2019 Mar 23"