Recent cryovolcanism in Virgil Fossae on Pluto Dale Cruikshank, Orkan Umurhan, Ross Beyer, B Schmitt, James Keane, Kirby Runyon, Dimitra Atri, Oliver White, Isamu Matsuyama, Jeffrey Moore, et al. To cite this version: Dale Cruikshank, Orkan Umurhan, Ross Beyer, B Schmitt, James Keane, et al.. Recent cryovolcanism in Virgil Fossae on Pluto. Icarus, Elsevier, 2019, 330, pp.155-168. 10.1016/j.icarus.2019.04.023. hal- 03098929 HAL Id: hal-03098929 https://hal.archives-ouvertes.fr/hal-03098929 Submitted on 5 Jan 2021 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Cruikshank et al; 201, Icarus, 330, 155-168 - revised Recent Cryovolcanism in Virgil Fossae on Pluto Revised April 19, 2019 Dale P. Cruikshank*a, Orkan M.Umurhana, Ross A. Beyera, Bernard Schmittb, James T. Keanec, Kirby D. Runyond, Dimitra Atrie,f, Oliver L. Whitea, Isamu Matsuyamag, Jeffrey 5 M. Moorea, William B. McKinnonh, Scott A. Sandforda, Kelsi N. Singeri, William M. Grundyj, Cristina M. Dalle Orea,k, Jason C. Cookl, Tanguy Bertranda, S. Alan Sterni, Catherine B. Olkini, Harold A. Weaverd, Leslie A. Youngi, John R. Spenceri, Carey M. Lissed, Richard P. Binzelm, Alissa M. Earlem, Stuart J. Robbinsi, G. Randall Gladstonen, Richard J. Cartwrighta,k, Kimberly Ennicoa, 10 *Corresponding author aNASA Ames Research Center, Moffett Field, CA, United States bUniversité Grenoble Alpes, CNRS, IPAG, Grenoble, France cCalifornia Institute of Technology, Pasadena, CA, United States 15 dApplied Physics Laboratory, Johns Hopkins University, Laurel, MD, United States eNew York University Abu Dhabi, Abu Dhabi, United Arab Emirates fBlue Marble Space Institute, Seattle, WA, United States gLunar and Planetary Laboratory, University of Arizona, Tucson, AZ, United States hWashington University, St. Louis, MO, United States 20 iSouthwest Research Institute, Boulder, CO, United States jLowell Observatory, Flagstaff, AZ, United States kSETI Institute, Mountain View, CA, United States lPinhead Institute, Telluride, CO, United States mMassachusetts Institute of Technology, Cambridge, MA, United States 25 nSouthwest Research Institute, San Antonio, TX, United States Additional author information: Dale P. Cruikshank 30 MS 246-6 NASA Ames Research Center Moffett Field, CA 94035 [email protected] 650-604-1444 35 FAX 650-604-6779 Umurhan, Orkan M. MS 246-3 NASA Ames Research Center 40 Moffett Field, CA 94035 [email protected] 650-604-5000 1 J. M. Moore 45 MS 246-3 NASA Ames Research Center Moffett Field, CA 94035 [email protected] 60-604-5529 50 W. M. Grundy Lowell Observatory 1400 W. Mars Hill Rd. Flagstaff, AZ 86001 55 [email protected] S. A. Stern Southwest Research Institute 1050 Walnut St. Ste. 400 60 Boulder, CO 80302 [email protected] 303-546-9670 C. B. Olkin 65 Southwest Research Institute 1050 Walnut St. Boulder, CO 80302 [email protected] 303-546-9670 70 L. A. Young Southwest Research Institute 1050 Walnut St. Boulder, CO 80302 75 [email protected] 303-546-9670 K. Ennico NASA Ames Research Center 80 Moffett Field, CA 94035 [email protected] 650-604-6067 H. A. Weaver 85 Applied Physics Lab. Johns Hopkins University Laurel, MD [email protected] 443-778-8078 2 90 C. M. Dalle Ore MS 245-6 NASA Ames Research Center Moffett Field, CA 94035 95 650-604-6151 [email protected] 650-604-6151 C. M. Lisse 100 Applied Physics Lab. Johns Hopkins University Laurel, MD [email protected] 240-228-0535 105 K. D. Runyon Applied Physics Lab. Johns Hopkins University Laurel, MD 110 [email protected] 443-778-5000 R. A. Beyer MS 245-3 115 NASA Ames Research Center Moffett Field, CA 94035 [email protected] 650-604-0324 120 B. Schmitt Université Grenoble Alpes CNRS, IPAG Grenoble, France F-38000 [email protected] 125 Richard J. Cartwright SETI Institute 189 N. Bernardo Ave., Ste 200 Mountain View, CA 94043 130 [email protected] Dimitra Atri New York University Abu Dhabi Saadiyat Island, Abu Dhabi 135 United Arab Emirates 3 [email protected] Isamu Matsyuama Lunar and Planetary Lab. 140 University of Arizona Tucson, AZ 85721 [email protected] John Spencer 145 Southwest Research Institute 1050 Walnut St. Boulder, CO 80302 [email protected] 303-546-9670 150 G. Randall Gladstone Southwest Research Institute 6220 Culebra Rd. San Antonio, TX 78238 155 [email protected] James T. Keane California Institute of Technology Pasadena, CA 91125 160 [email protected] 626-395-4241 Oliver L. White MS 245-3 165 NASA Ames Research Institute Moffett Field, CA 94035 [email protected] Scott A. Sandford 170 MS 245-6 NASA Ames Research Institute Moffett Field, CA 94035 [email protected] 175 Wm. B. McKinnon Washington University St. Louis, MO [email protected] 180 Jason C. Cook Pinhead Institute 4 Telluride, CO [email protected] 185 T. Bertrand MS 245-3 NASA Ames Research Institute Moffett Field, CA 94035 [email protected] 190 650-537-5334 Richard P. Binzel Massaschusetts Institute of Technology Cambridge, MA 195 [email protected] Alissa M. Earle Massaschusetts Institute of Technology Cambridge, MA 200 [email protected] Stuart Robbins Southwest Research Institute 1050 Walnut St. 205 Boulder, CO 80302 303-546-9670 [email protected] Kelsi N. Singer 210 Southwest Research Institute 1050 Walnut St. Boulder, CO 80302 303-546-9670 [email protected] 215 Key Words -Pluto, surface -Ices, IR spectroscopy 220 -Interiors -Organic chemistry -Volcanism 225 Highlights 5 •A tectonic structure (Virgil Fossae) on Pluto may be a source of a cryolava that has been erupted onto the planet's surface. 230 •The putative cryolava consists primarily of H2O, but it carries the spectral signature of ammonia (NH3), which may occur as an ammonia hydrate or an ammoniated salt. It also carries a distinctively colored component thought to be complex organic matter (a tholin). •Because NH3 in its various forms is susceptible to destruction by UV photons and 235 charged particles, its presence suggests emplacement on Pluto's surface sometime in the past billion years. •In addition to the debouchment of cryolava along fault lines in Virgil Fossae, fountaining from one or more associated sites appears to have distributed a mantling 240 layer covering a few thousand square kilometers. •The planet-scale geophysical setting of Virgil Fossae in a large region stressed by factors related to the nitrogen glacier Sputnik Planitia is consistent with extensional fracturing. Some fractures appear to have facilitated the emergence of a cryolava from one or more 245 reservoirs in the subsurface. Abstract 250 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 H2O ice in which there is entrained opaque red-colored matter of unknown composition. The H2O ice is also seen to carry spectral signatures at 1.65 and 2.2 μm of NH3 in some 255 form, possibly as a hydrate, an ammoniated salt, or some other compound. Model calculations of NH3 destruction in H2O ice by galactic cosmic rays suggest that the 9 maximum lifetime of NH3 in the uppermost meter of the exposed surface is ~10 years, while considerations of Lyman-α ultraviolet and solar wind charged particles suggest shorter timescales by a factor of 10 or 100. Thus, 109 y is taken as an upper limit to the 260 age of the emplacement event, and it could be substantially younger. The red colorant in the ammoniated H2O 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 265 New Horizons imaging spectrometer and the signal precision of the data, apart from the H2O and NH3 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 270 material it may incorporate organics inherited from the solar nebula, further processed in a warm aqueous environment inside Pluto. 6 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 275 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 H2O ice deposits in and around Virgil Fossae. Models of a cryoflow emerging from sources in Virgil Fossae indicate that the lateral 280 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.