Percorrer por autor "Filacchione, G."
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- Characterization of Titan’s Ontario Lacus region from Cassini/VIMS observationsPublication . Moriconi, M. L.; Lunine, J. I.; Adriani, A.; D’Aversa, E.; Negrão, A.; Filacchione, G.; Coradini, A.Liquid hydrocarbons were long predicted on Titan's surface before the RADAR instrument onboard Cassini detected lakes poleward of 70°N in July 2006. Before that the Cassini Imaging Science Subsystem (ISS) observed a lake-like feature in the South Pole, named Ontario Lacus, in July 2004. Here we analyze one observation of Ontario Lacus taken by the Visual and Infrared Mapping Spectrometer (VIMS) on 2007 December 5, during the T 38 flyby. This is the best spatially resolved image of a Titan lake to date by an imaging spectrometer, and has been previously reported in Brown et al. (Brown, R.H., Soderblom, L.A., Soderblom, J.M., Clark, R.N., Jaumann, R., Barnes, J.W., Sotin, C., Buratti, B., Baines, K.H., Nicholson, P.D. [2008]. Nature 454, 607-610) and in Barnes et al. (Barnes, J.W. et al. [2009]. Icarus 201, 217-225). The observing geometry and our data processing will be explained, followed by a discussion of the main characteristics of the image. The analyzed image covers a small portion of Ontario Lacus and shows what appears from RADAR data to be a region of modest slope (" ramp" ) adjacent to the dark lake itself. Our analysis of 5.0 μm spectral data suggests that the previously reported absorption feature of ethane seen at shorter wavelengths may be produced by damp sediments adjacent to the main liquid basin. The latter appears to be absorbing all of the photons incident upon it in the 5 μm spectral region and shows no discernible absorption features. A characterization of the basin composition and morphology is developed with the help of ISS and RADAR observations. The simplest model consistent with the data is an optically deep lake surrounded by a region in which ethane, propane, possibly methane, and other, less volatile hydrocarbons and nitriles are present mixed into spectroscopically neutral sediments. The dominance of relatively low vapor pressure organics outside the lake itself suggests a retreat of Ontario Lacus associated with evaporation on seasonal or longer timescales, consistent with analysis of RADAR and ISS images.
- Correlations between VIMS and RADAR data over the surface of Titan: Implications for Titan’s surface propertiesPublication . Tosi, F.; Orosei, R.; Seu, R.; Coradini, A.; Lunine, J. I.; Filacchione, G.; Gavrishin, A. I.; Capaccioni, F.; Cerroni, P.; Adriani, A.; Moriconi, M. L.; Negrão, A.; Flamini, E.; Brown, R. H.; Wye, L. C.; Janssen, M.; West, R. D.; Barnes, J. W.; Wall, S. D.; Clark, R. N.; Cruikshank, D. P.; McCord, T. B.; Nicholson, P. D.; Soderblom, J. M.We apply a multivariate statistical method to Titan data acquired by different instruments onboard the Cassini spacecraft. We have searched through Cassini/VIMS hyperspectral cubes, selecting those data with convenient viewing geometry and that overlap with Cassini/RADAR scatterometry footprints with a comparable spatial resolution. We look for correlations between the infrared and microwave ranges the two instruments cover. Where found, the normalized backscatter cross-section obtained from the scatterometer measurement, corrected for incidence angle, and the calibrated antenna temperature measured along with the scatterometry echoes, are combined with the infrared reflectances, with estimated errors, to produce an aggregate data set, that we process using a multivariate classification method to identify homogeneous taxonomic units in the multivariate space of the samples.In medium resolution data (from 20 to 100. km/pixel), sampling relatively large portions of the satellite's surface, we find regional geophysical units matching both the major dark and bright features seen in the optical mosaic. Given the VIMS cubes and RADAR scatterometer passes considered in this work, the largest homogeneous type is associated with the dark equatorial basins, showing similar characteristics as each other on the basis of all the considered parameters.On the other hand, the major bright features seen in these data generally do not show the same characteristics as each other. Xanadu, the largest continental feature, is as bright as the other equatorial bright features, while showing the highest backscattering coefficient of the entire satellite. Tsegihi is very bright at 5 μm but it shows a low backscattering coefficient, so it could have a low roughness on a regional scale and/or a different composition. Another well-defined region, located southwest of Xanadu beyond the Tui Regio, seems to be detached from the surrounding terrains, being bright at 2.69, 2.78 and 5 μm but having a low radar brightness. In this way, other units can be found that show correlations or anti-correlations between the scatterometric response and the spectrophotometric behavior, not evident from the optical remote sensing data.