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Prebiotic Chemistry of Pluto

Cruikshank, D. P. and Materese, C. K. and Pendleton, Y. J. and Boston, P. J. and Grundy, W. M. and Schmitt, B. and Lisse, C. M. and Runyon, K. D. and Keane, J. T. and Beyer, R. A. and Summers, M. E. and Scipioni, F. and Stern, S. A. and Dalle Ore, C. M. and Olkin, C. B. and Young, L. A. and Ennico, K. and Weaver, H. A. and Bray, V. J. (2019) Prebiotic Chemistry of Pluto. Astrobiology, 19 (7). pp. 831-848. ISSN 1557-8070.

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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_2O 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_2O 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_2O-NH_3ice 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_2O 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.

Item Type:Article
Related URLs:
URLURL TypeDescription
Lisse, C. M.0000-0002-9548-1526
Keane, J. T.0000-0002-4803-5793
Olkin, C. B.0000-0002-5846-716X
Ennico, K.0000-0002-8847-8492
Weaver, H. A.0000-0003-0951-7762
Additional Information:© 2019 Mary Ann Liebert, Inc. Submitted 28 June 2018; Accepted 11 January 2019. This work was supported by NASA's New Horizons mission. No competing financial interests exist for any author.
Funding AgencyGrant Number
Subject Keywords:Pluto; Tholin; Ice; Nucleobase
Issue or Number:7
Record Number:CaltechAUTHORS:20190401-100241606
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Official Citation:D.P. Cruikshank, C.K. Materese, Y.J. Pendleton, P.J. Boston, W.M. Grundy, B. Schmitt, C.M. Lisse, K.D. Runyon, J.T. Keane, R.A. Beyer, M.E. Summers, F. Scipioni, S.A. Stern, C.M. Dalle Ore, C.B. Olkin, L.A. Young, K. Ennico, H.A. Weaver, and V.J. Bray. Astrobiology. Jul 2019.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:94312
Deposited By: Tony Diaz
Deposited On:01 Apr 2019 17:16
Last Modified:31 Oct 2019 01:59

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