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Recent cryovolcanism in Virgil Fossae on Pluto

Cruikshank, Dale P. and Keane, James T. (2019) Recent cryovolcanism in Virgil Fossae on Pluto. Icarus, 330 . pp. 155-168. ISSN 0019-1035.

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The Virgil Fossae region on Pluto exhibits three spatially coincident properties that are suggestive of recent cryovolcanic activity over an area approximately 300 by 200 km. Situated in the fossae troughs or channels and in the surrounding terrain are exposures of H_2O ice in which there is entrained opaque red-colored matter of unknown composition. The H_2O ice is also seen to carry spectral signatures at 1.65 and 2.2 μm of NH_3 in some form, possibly as a hydrate, an ammoniated salt, or some other compound. Model calculations of NH_3 destruction in H_2O ice by galactic cosmic rays suggest that the maximum lifetime of NH_3 in the uppermost meter of the exposed surface is ~10^9 years, while considerations of Lyman-α ultraviolet and solar wind charged particles suggest shorter timescales by a factor of 10 or 100. Thus, 10^9 y is taken as an upper limit to the age of the emplacement event, and it could be substantially younger. The red colorant in the ammoniated H_2O in Virgil Fossae and surroundings may be a macromolecular organic material (tholin) thought to give color to much of Pluto's surface, but probably different in composition and age. Owing to the limited spectral range of the New Horizons imaging spectrometer and the signal precision of the data, apart from the H_2O and NH_3 signatures there are no direct spectroscopic clues to the chemistry of the strongly colored deposit on Pluto. We suggest that the colored material was a component of the fluid reservoir from which the material now on the surface in this region was erupted. Although other compositions are possible, if it is indeed a complex organic material it may incorporate organics inherited from the solar nebula, further processed in a warm aqueous environment inside Pluto. A planet-scale stress pattern in Pluto's lithosphere induced by true polar wander, freezing of a putative interior ocean, and surface loading has caused fracturing in a broad arc west of Sputnik Planitia, consistent with the structure of Virgil Fossae and similar extensional features. This faulting may have facilitated the ascent of fluid in subsurface reservoirs to reach the surface as flows and as fountains of cryoclastic materials, consistent with the appearance of colored, ammoniated H_2O ice deposits in and around Virgil Fossae. Models of a cryoflow emerging from sources in Virgil Fossae indicate that the lateral extent of the flow can be several km (Umurhan et al., 2019). The deposit over the full length (>200 km) of the main trough in the Virgil Fossae complex and extending through the north rim of Elliot crater and varying in elevation over a range of ~2.5 km, suggests that it debouched from multiple sources, probably along the length of the strike direction of the normal faults defining the graben. The source or sources of the ammoniated H_2O are one or more subsurface reservoirs that may or may not connect to the global ocean postulated for Pluto's interior. Alternatives to cryovolcanism in producing the observed characteristics of the region around Virgil Fossae are explored in the discussion section of the paper.

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Keane, James T.0000-0002-4803-5793
Additional Information:© 2019 Published by Elsevier Inc. Received 21 November 2018, Revised 19 April 2019, Accepted 24 April 2019, Available online 25 April 2019. We thank Drs. Luis Teodoro for helpful discussions about GCR penetration in ices, Francis Nimmo on the dispersal of cryoclastics, and Ted Roush for advice on the spectra of ammoniated salts. We thank two anonymous referees for their careful reading and thoughtful comments that led to improvements in this paper. Spectra of ammoniated salts were found in the Brown University RELAB data base. This work is supported primarily by NASA's New Horizons project.
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Subject Keywords:Pluto; Surface; Ices; IR spectroscopy; Interiors; Organic chemistry; Volcanism
Record Number:CaltechAUTHORS:20190426-080038903
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Official Citation:Dale P. Cruikshank, Orkan M. Umurhan, Ross A. Beyer, Bernard Schmitt, James T. Keane, Kirby D. Runyon, Dimitra Atri, Oliver L. White, Isamu Matsuyama, Jeffrey M. Moore, William B. McKinnon, Scott A. Sandford, Kelsi N. Singer, William M. Grundy, Cristina M. Dalle Ore, Jason C. Cook, Tanguy Bertrand, S. Alan Stern, Catherine B. Olkin, Harold A. Weaver, Leslie A. Young, John R. Spencer, Carey M. Lisse, Richard P. Binzel, Alissa M. Earle, Stuart J. Robbins, G. Randall Gladstone, Richard J. Cartwright, Kimberly Ennico, Recent cryovolcanism in Virgil Fossae on Pluto, Icarus, Volume 330, 2019, Pages 155-168, ISSN 0019-1035, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95005
Deposited By: Tony Diaz
Deposited On:26 Apr 2019 16:48
Last Modified:09 May 2019 17:15

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