Paper No. 211-4
Presentation Time: 2:30 PM
GEOPHYSICS OF THE PLUTO SYSTEM
NIMMO, Francis1, MCKINNON, William B.
2, MOORE, Jeffrey M.
3, SCHENK, Paul M.
4, ROBERTS, James H.
5, BEYER, Ross
6, BIERSON, Carver J.
1, STERN, S. Alan
7, OLKIN, Cathy
8, LISSE, Carey M.
9 and UMURHAN, Orkan
10, (1)Department of Earth and Planetary Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, (2)Washington University, Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, One Brookings Drive, Saint Louis, MO 63130, (3)NASA Ames Research Center, Space Science Division, MS-245-3, Moffett Field, CA 95129, (4)Lunar and Planetary Institute, Universities Space Research Association, 3600 Bay Area Boulevard, Houston, TX 77058, (5)Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, (6)NASA, Ames Research Center, Moffet Field, CA 94035, (7)Southwest Research Institute, 1050 Walnut Street, Boulder, CO 80302, (8)Department of Space Studies, Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80302, (9)Applied Physics Laboratory, Johns Hopkins University, 11100 Johns Hopkins Rd, Laurel, MD 20723, (10)NASA Ames Research Center, Space Science Division, MS-245-3, Moffett Field, CA 94035, fnimmo@es.ucsc.edu
What are the internal structures of Pluto and Charon? How did they form and evolve? New Horizons data [1] provide the answer to some of these questions. Pluto and Charon have bulk densities differing by 9% and neither show fossil rotational bulges [2]. The different densities cannot be due simply to differential pore closure [3], and instead imply a different bulk composition, providing a constraint on how Pluto and Charon formed [4-5]. On both bodies the absence of a bulge and predominantly extensional tectonics [6] suggest an ancient ocean which re-froze [7,8]. A present-day ocean on Pluto implies that the shell is cold and conductive [7], perhaps because of the presence of ammonia. On Charon, an ocean would survive only if significant ammonia is present. Refreezing of an ice shell pressurizes the ocean [9], which may help explain apparently cryovolcanic features on both bodies [6].
The Sputnik Planum basin on Pluto may be an ancient impact feature. It is now buried with several km of solid N2 ice. This ice has a young surface age and appears to be convecting [10,11], driven by heat leaking out of the silicate interior. Sputnik Planum’s location close to the tidal axis may be a result of loading-driven reorientation [12-14]. Such reorientation likely requires a subsurface ocean and is also consistent with a thick elastic ice shell at present [13].
[1] Stern et al. Science 2015 [2] Nimmo et al., Icarus in press [3] Bierson et al., LPSC 2016 [4] Canup, Science 2005 [5] Desch et al., Icarus 2015 [6] Moore et al., Science 2016 [7] Robuchon & Nimmo, Icarus 2011 [8] Hammond et al., GRL 2016 [9] Manga & Wang, GRL 2007 [10] McKinnon et al., Nature 2016 [11] Trowbridge et al., Nature 2016 [12] Hamilton, Fall AGU 2015 [13] Nimmo et al., LPSC 2016 [14] Keane et al., LPSC 2016
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