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Correlations between Cassini VIMS spectra and RADAR SAR images: Implications for Titan’s surface composition and the character of the Huygens Probe Landing Site

Soderblom, Laurence A. and Baines, Kevin H. and Buratti, Bonnie J. and Elachi, Charles and Janssen, Michael A. and Lopes, Rosaly M. and Wall, Stephen D. (2007) Correlations between Cassini VIMS spectra and RADAR SAR images: Implications for Titan’s surface composition and the character of the Huygens Probe Landing Site. Planetary and Space Science, 55 (13). pp. 2025-2036. ISSN 0032-0633. https://resolver.caltech.edu/CaltechAUTHORS:20121121-090254426

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Abstract

Titan's vast equatorial fields of RADAR-dark longitudinal dunes seen in Cassini RADAR synthetic aperture images correlate with one of two dark surface units discriminated as “brown” and “blue” in Visible and Infrared Mapping Spectrometer (VIMS) color composites of short-wavelength infrared spectral cubes (RGB as 2.0, 1.6, 1.3 μm). In such composites bluer materials exhibit higher reflectance at 1.3 μm and lower at 1.6 and 2.0 μm. The dark brown unit is highly correlated with the RADAR-dark dunes. The dark brown unit shows less evidence of water ice suggesting that the saltating grains of the dunes are largely composed of hydrocarbons and/or nitriles. In general, the bright units also show less evidence of absorption due to water ice and are inferred to consist of deposits of bright fine precipitating tholin aerosol dust. Some set of chemical/mechanical processes may be converting the bright fine-grained aerosol deposits into the dark saltating hydrocarbon and/or nitrile grains. Alternatively the dark dune materials may be derived from a different type of air aerosol photochemical product than are the bright materials. In our model, both the bright aerosol and dark hydrocarbon dune deposits mantle the VIMS dark blue water ice-rich substrate. We postulate that the bright mantles are effectively invisible (transparent) in RADAR synthetic aperture radar (SAR) images leading to lack of correlation in the RADAR images with optically bright mantling units. RADAR images mostly show only dark dunes and the water ice substrate that varies in roughness, fracturing, and porosity. If the rate of deposition of bright aerosol is 0.001–0.01 μm/yr, the surface would be coated (to optical instruments) in hundreds-to-thousands of years unless cleansing processes are active. The dark dunes must be mobile on this very short timescale to prevent the accumulation of bright coatings. Huygens landed in a region of the VIMS bright and dark blue materials and about 30 km south of the nearest occurrence of dunes visible in the RADAR SAR images. Fluvial/pluvial processes, every few centuries or millennia, must be cleansing the dark floors of the incised channels and scouring the dark plains at the Huygens landing site both imaged by Descent Imager/Spectral Radiometer (DISR).


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1016/j.pss.2007.04.014DOIArticle
http://www.sciencedirect.com/science/article/pii/S0032063307001304PublisherArticle
ORCID:
AuthorORCID
Soderblom, Laurence A.0000-0002-0917-853X
Janssen, Michael A.0000-0001-5476-731X
Additional Information:© 2007 Elsevier Ltd. Accepted 13 April 2007. Available online 27 April 2007. This work was funded by the Cassini Project conducted for NASA by the Jet Propulsion Laboratory, California Institute of Technology. The authors wish to thank Athena Coustenis, Jeffery Johnson, Christopher McKay, Timothy Titus, and an unnamed reviewer for insightful and constructive criticism.
Funders:
Funding AgencyGrant Number
NASA/JPL/CaltechUNSPECIFIED
Subject Keywords: Titan; VIMS; Radar; SAR; DISR; Dunes; Mantles; Coatings; Substrate; Water ice; Hydrocarbons; Titriles; Tholin; Aerosols
Issue or Number:13
Record Number:CaltechAUTHORS:20121121-090254426
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20121121-090254426
Official Citation:Laurence A. Soderblom, Randolph L. Kirk, Jonathan I. Lunine, Jeffrey A. Anderson, Kevin H. Baines, Jason W. Barnes, Janet M. Barrett, Robert H. Brown, Bonnie J. Buratti, Roger N. Clark, Dale P. Cruikshank, Charles Elachi, Michael A. Janssen, Ralf Jaumann, Erich Karkoschka, Stéphane Le Mouélic, Rosaly M. Lopes, Ralph D. Lorenz, Thomas B. McCord, Philip D. Nicholson, Jani Radebaugh, Bashar Rizk, Christophe Sotin, Ellen R. Stofan, Tracie L. Sucharski, Martin G. Tomasko, Stephen D. Wall, Correlations between Cassini VIMS spectra and RADAR SAR images: Implications for Titan's surface composition and the character of the Huygens Probe Landing Site, Planetary and Space Science, Volume 55, Issue 13, November 2007, Pages 2025-2036, ISSN 0032-0633, 10.1016/j.pss.2007.04.014. (http://www.sciencedirect.com/science/article/pii/S0032063307001304)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35596
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:21 Nov 2012 17:25
Last Modified:03 Oct 2019 04:29

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