HR: 15:30h
AN: P14A-01    [Abstracts]
TI: Cassini VIMS Photometric Investigation of Selected Features on the Surface of Titan: Relevance to Widespread Precipitation.
AU: * Nelson, R M
EM: robert.m.nelson@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: Brown, R H
EM: rhb@lpl.arizona.edu
AF: U of Arizona, Lunar and Planetary Laboratory,, Tucson, AZ 85721 United States
AU: Hapke, B W
EM: hapke@pitt.edu
AF: U of Pittsburgh, Dept of Geology and Planetary Science, Pittsburgh, PA 15260 United States
AU: Smythe, W D
EM: william.d.smythe@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: Kamp, L
EM: lucas.kamp@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: Boryta, M
EM: mboryta@oco.net
AF: Mount San Antonio College, Dept of Geology, Walnut, CA 95641
AU: Baines, K H
EM: Kevin.h.baines@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: Bellucci, G
EM: giancarlo.bellucci@ifsi.rm.cnr.it
AF: Istituto di Astrofisica Spaziale, Rome, Rome, Italy
AU: Biebring, J
EM: bibring@ias.fr
AF: Universite de Paris Sud-Orsay, Paris Sud-Orsay, Paris, France
AU: Buratti, B J
EM: bonnie.j.buratti@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: Capaccioni, F
EM: capaccio@ias.rm.cnr.it
AF: Istituto di Astrofisica Spaziale, Rome, Rome, Italy
AU: Cerroni, P
EM: priscio@ias.rm.cnr.it
AF: Istituto di Astrofisica Spaziale, Rome, Rome, Italy
AU: Clark, R N
EM: rclark@speclab.cr.usgs.gov
AF: United States Geological Survey, Denver Field Office, Denver, CO United States
AU: Coradini, A
EM: coradini@ias.rm.cnr.it
AF: Istituto di Astrofisica Spaziale, Rome, Rome, Italy
AU: Cruikshank, D P
EM: dcruikshank@mail.arc.nasa.gov
AF: NASA AMES Research Center, Mountain View, Mountain View, CA 94035
AU: Drossart, P
EM: Pierre.Drossart@obspm.fr
AF: Observatoire de Paris-Meudon, Paris-Meudon, Paris-Meudon, France
AU: Formisano, V
EM: formisan@nike.ifsi.rm.cnr.it
AF: Istituto di Astrofisica Spaziale, Rome, Rome, Italy
AU: Jaumann, R
EM: ralf.jaumann@dlr.de
AF: Institute for Planetary Exploration, DLR,, Berlin, Berlin, Germany
AU: Langevin, Y
EM: langevin@ias.fr
AF: Universite de Paris Sud-Orsay, Paris Sud-Orsay, Paris, France
AU: Matson, D L
EM: dennis.l.matson@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: McCord, T B
EM: mccordtb@aol.com
AF: University of Washington,, Seattle, Seattle, WA 85703 United States
AU: Mennella, V
EM: mennella@astrna.na.astro.it
AF: Osservatorio Astronomico di Capodimonte, Napoli, Naples, Italy
AU: Nicholson, P D
EM: nicholson@astrosun.astro.cornell.edu
AF: Cornell University, Ithaca Campus, Ithaca, NY 14853 United States
AU: Sicardy, B
EM: sicardy@mesiob.obspm.fr
AF: NASA AMES Research Center, Mountain View, Mountain View, CA 94035
AU: Sotin, C
EM: sotin@chimie.univ-nantes.fr
AF: University of Nantes, Nantes Campus, Nantes, France
AB: Photometric analysis of Cassini VIMS images of Titan suggests a hemispheric albedo dichotomy and that palimpsests are present. This implies long term surface albedo stability, inconsistent with widespread precipitation on Titan. We calculate linear phase coefficients for Titan's surface and find that it behaves like most planetary regoliths. Photometric anlaysis of Titan's approximately opposite hemispheres finds the most reflective regions (r=20%) are between longitude 50-130°. The lowest albedo regions (A~6%) are found near zero deg, consistent with previous observations (1,2,4,5,6). The most reflective units on Titan's leading side have higher reflectance than the most reflective units on the approximately opposite hemisphere. This is also true for the most absorbing units. VIMS finds features on Titan which are similar to circular features exhibiting topographic relief caused by impact events on a wide range of solar system objects. For two circular regions we searched for vertical relief by comparing photometric profiles with the profiles expected from model craters using the bi-directional reflectance equations developed by Hapke (1993). Despite our best effort to adjust the depression parameters to fit our data, no model is consistent with a craterlike depression. We suggest that these are albedo features and are not caused by topographic relief. They are consistent with palimpsests - impact events where the vertical relief has been lost to lithospheric plastic flow over time and remain only as expressions of darker reflectance on the surface. If so, their persistence on the surface suggests that widespread weathering processes, such as a planet-wide precipitation of aerosols, on Titan are severely limited. 1Campbell et al, Science, 302, 431-434, 2003 2Combes et al., Icarus, 129, 482-497, 1997 3Gibbard et al., Icarus, 139, 189-201, 1999. 4Hapke 1993, Theory of Reflectance and Emittance Spectroscopy, Cambridge. 5Meier et al., Icarus, 145, 463-473, 2000. 6Smith et al., 119, 336-349, 1996
DE: 6008 Composition
DE: 6055 Surfaces and interiors
DE: 6062 Satellites
DE: 6207 Comparative planetology
DE: 6280 Saturnian satellites
SC: Planetary Sciences [P]
MN: 2005 Joint Assembly