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Hydrocarbons on Saturn's satellites Iapetus and Phoebe |
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| Authors: | Dale P Cruikshank Eric Wegryn RH Brown BJ Buratti TB McCord YJ Pendleton G Filacchione P Cerroni R Jaumann KH Baines G Bellucci Y Langevin DL Matson P Drossart |
| Institution: | a NASA Ames Research Center, Moffett Field, CA 94035, USA b SETI Institute, 515 N. Whisman Road, Mountain View, CA 94043, USA c Lunar and Planetary Laboratory and Steward Observatory, University of Arizona, Tucson, AZ 85721, USA d Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, USA e Institut d'Astrophysique Spatiale, Université de Paris-Sud, Bâtiment 121, F-91405 Orsay, France f US Geological Survey, Mail Stop 964, Box 25046, Denver Federal Center, Denver, CO 80225, USA g Space Science Institute NW, 22 Fiddler's Road, Winthrop, WA 98862, USA h Cornell University, 418 Space Sciences Building, Ithaca, NY 14853, USA i Institute for Astronomy, University of Hawaii, 2680 Woodlawn Dr., Honolulu, HI 96822, USA j INAF-IASF, Istituto di Astrofisica Spaziale e Fisica Cosmica, Via Fosso del Cavaliere 100, I-00133 Roma, Italy k DLR, Institute for Planetary Exploration, Rutherfordstrasse 2, D-12489 Berlin, Germany l University of Nantes, B.P. 92208, 2 rue de la Houssinière, 44072 Nantes Cedex 3, France m INAF-IASF Istituto dello Spazio Interplanetario, Via del Fosso del Cavaliere 100, 00133 Roma, Italy n Observatoire de Paris-Meudon, Département Recherche Spatial, 5 Place Jules Jannsen, 95129 Meudon Cedex, France o INAF-OAC, Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, I-80131 Napoli, Italy |
| Abstract: | Material of low geometric albedo (pV?0.1) is found on many objects in the outer Solar System, but its distribution in the saturnian satellite system is of special interest because of its juxtaposition with high-albedo ice. In the absence of clear, diagnostic spectral features, the composition of this low-albedo (or “dark”) material is generally inferred to be carbon-rich, but the form(s) of the carbon is unknown. Near-infrared spectra of the low-albedo hemisphere of Saturn's satellite Iapetus were obtained with the Visible-Infrared Mapping Spectrometer (VIMS) on the Cassini spacecraft at the fly-by of that satellite of 31 December 2004, yielding a maximum spatial resolution on the satellite's surface of ∼65 km. The spectral region 3-3.6 μm reveals a broad absorption band, centered at 3.29 μm, and concentrated in a region comprising about 15% of the low-albedo surface area. This is identified as the C H stretching mode vibration in polycyclic aromatic hydrocarbon (PAH) molecules. Two weaker bands attributed to CH2 stretching modes in aliphatic hydrocarbons are found in association with the aromatic band. The bands most likely arise from aromatic and aliphatic units in complex macromolecular carbonaceous material with a kerogen- or coal-like structure, similar to that in carbonaceous meteorites. VIMS spectra of Phoebe, encountered by Cassini on 11 June 2004, also show the aromatic hydrocarbon band, although somewhat weaker than on Iapetus. The origin of the PAH molecular material on these two satellites is unknown, but PAHs are found in carbonaceous meteorites, cometary dust particles, circumstellar dust, and interstellar dust. |
| Keywords: | Iapetus Organic chemistry Satellites composition Spectroscopy |
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