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Cassini-VIMS at Jupiter: solar occultation measurements using Io |
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| Authors: | V Formisano E D'Aversa KH Baines RH Brown F Capaccioni RN Clark DP Cruikshank R Jaumann DL Matson V Mennella PD Nicholson C Sotin G Hansen M Showalter |
| Institution: | a Istituto di Fisica dello Spazio Interplanetario, CNR, Rome, Italy b Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA c Institut d'Astrophysique Spatiale, Université de Paris, France d Lunar and Planetary Lab and Stewart Observatory , University of Arizona, Tucson, AZ, USA e Istituto di Astrofisica Spaziale e Fisica Cosmica, CNR, Rome, Italy f US Geological Survey, Denver, CO, USA g NASA Ames Research Center, Moffett Field, CA, USA h Observatoire de Paris, Meudon, France i Institute for Planetary Exploration, DLR, Germany j Department of Earth and Space Sciences, University of Washington, Seattle, WA, USA k INAF-Osservatorio Astronomico di Capodimonte, Italy l Cornell University, Astronomy Department, Ithaca, NY, USA m Laboratoire de Planetologie et Geodinamique, Université de Nantes, France |
| Abstract: | We report unusual and somewhat unexpected observations of the jovian satellite Io, showing strong methane absorption bands. These observations were made by the Cassini VIMS experiment during the Jupiter flyby of December/January 2000/2001. The explanation is straightforward: Entering or exiting from Jupiter's shadow during an eclipse, Io is illuminated by solar light which has transited the atmosphere of Jupiter. This light, therefore becomes imprinted with the spectral signature of Jupiter's upper atmosphere, which includes strong atmospheric methane absorption bands. Intercepting solar light refracted by the jovian atmosphere, Io essentially becomes a “mirror” for solar occultation events of Jupiter. The thickness of the layer where refracted solar light is observed is so large (more than 3000 km at Io's orbit), that we can foresee a nearly continuous multi-year period of similar events at Saturn, utilizing the large and bright ring system. During Cassini's 4-year nominal mission, this probing technique should reveal information of Saturn's atmosphere over a large range of southern latitudes and times. |
| Keywords: | Occultations Jupiter Infrared observations |
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