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Reggie L. Hudson - One of the best experts on this subject based on the ideXlab platform.
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Thermal Reactions of H2O2 on Icy Satellites and Small Bodies: Descent with Modification?
2012Co-Authors: Reggie L. Hudson, Mark J. LoefflerAbstract:Abstract for DPS Meeting - 2012 Thermal Reactions of H20 2 on Icy Satellites and Small Bodies: Descent with Modification? Reggie L. Hudson and Mark J. Loeffler Astrochemistry Laboratory NASA Goddard Space Flight Center Greenbelt, MD 20771 Magnetospheric radiation drives surface and near-surface chemistry on Europa, but below a few meters Europa's chemistry is hidden from direct observation. As an example, surface radiation chemistry converts H20 and S02 into H20 2 and (S04t, respectively, and these species will be transported downward (Greenberg, Astrobiology, 2010, 10,275) for possible thermally-driven reactions. However, while the infrared spectra and radiation chemistry of H202-containing ices are well documented, this molecule's thermally-induced solid-phase chemistry has seldom been studied. Here we report new results on thermal reactions in H20 + H20 2 + S02 ices at 50 -130 K. As an example of our results, we find that warming H20 + H20 2 + S02 ices promotes S02 oxidation to (S04)2-. These results have implications for the survival of H20 2 as it descends, with modification, towards a subsurface ocean on Europa. We suspect that such redox chemistry may explain some of the observations related to the presence and distribution of H20 2 across Europa's surface as well as the lack of H20 2 on Ganymede and Callisto. [This work was supported by NASA's Exobiology, Outer Planets, and Planetary Geology and Geophysics programs, and The Goddard Center for Astrobiology.]
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Thermal Reactions Between Sulfur Dioxide and H202 and Their Relevance to the Jovian Icy Satellites and Other Small Bodies
2011Co-Authors: Mark J. Loefler, Reggie L. HudsonAbstract:Laboratory experiments have demonstrated that magnetospheric radiation in the Jovian system drives reaction chemistry in ices at temperatures relevant to Europa and other Icy Satellites. Here we present new results on thermally-induced reactions occurring between 50 and 130 K in solid H2O + H2O2 + SO2 samples. In our studies, we find that warming our three component mixtures induces a thermal reaction that produces SO4(2-), and this reaction appears to consume equal amounts of H2O2 and SO2. We suspect that the results may explain some of the observations related to the presence and distribution H2O2 across Europa's surface as well as the lack of H2O2 on Ganymede and Callisto. If other molecules prove to be reactive with H2O2 at these or at even lower temperatures, then it may also explain why H2O2 has been absent from surfaces of many of the small Icy bodies that are known to be exposed to ionizing radiation.
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The Other Chemistry of the Jovian Icy Satellites - Low Energy and Sulfurous
2010Co-Authors: Reggie L. Hudson, Mark J. Loeffler, M. H. MooreAbstract:Spectra of Jupiter's Icy Satellites reveal surfaces dominated by H2O-ice with minor amounts of SO2 and other materials. The co-existence of H2O and SO2 in surfaces exposed to jovian magnetospheric radiation suggests that sulfuric acid (H2SO4) also could be present. This was noted by Carlson et al. (1999), who supported this suggestion with assignments of near-IR bands in Europa spectra to hydrated H2SO4. Laboratory experiments since have demonstrated radiolytically-driven syntheses in S- and SO2-containing H2O-Ices (Carlson et al., 2002; Moore et al., 2006). In the Cosmic Ice Laboratory, we recently have investigated the thermal chemistry of SO2 trapped in H2O-ice. IR spectra of H2O + SO2 mixtures recorded at 10 to 230 K were used to follow low-temperature reactions in the absence of radiation effects. No SO2 reactions were found at 10 K, but warming to more-relevant Europa temperatures produced both HSO3(-) and S2O5(2-). Added NH3 shifted the product composition toward SO3(2-) and away from the other ions. We find that H2O and SO2 react to produce sulfur oxyanions, such as bisulfite, that as much as 30% of the SO2 can be consumed through this reaction, and that the products remain in the ice when the temperature is lowered, indicating that these reactions are irreversible. Our results suggest that thermally-induced reactions can alter the chemistry at and below the surfaces of the Icy Satellites in the jovian system.
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Thermally‐induced chemistry and the Jovian Icy Satellites: A laboratory study of the formation of sulfur oxyanions
Geophysical Research Letters, 2010Co-Authors: Mark J. Loeffler, Reggie L. HudsonAbstract:[1] Laboratory experiments have demonstrated that magnetospheric radiation in the Jovian system drives reaction chemistry in ices at temperatures relevant to Europa and other Icy Satellites. Here we present new results on thermally-induced reactions at 50–100 K in solid H2O-SO2 mixtures, reactions that take place without the need for a high-radiation environment. We find that H2O and SO2 react to produce sulfur oxyanions, such as bisulfite, that as much as 30% of the SO2 can be consumed through this reaction, and that the products remain in the ice when the temperature is lowered, indicating that these reactions are irreversible. Our results suggest that thermally-induced reactions can alter the chemistry at temperatures relevant to the Icy Satellites in the Jovian system.
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thermally induced chemistry and the jovian Icy Satellites a laboratory study of the formation of sulfur oxyanions
Geophysical Research Letters, 2010Co-Authors: M J Loeffler, Reggie L. HudsonAbstract:[1] Laboratory experiments have demonstrated that magnetospheric radiation in the Jovian system drives reaction chemistry in ices at temperatures relevant to Europa and other Icy Satellites. Here we present new results on thermally-induced reactions at 50–100 K in solid H2O-SO2 mixtures, reactions that take place without the need for a high-radiation environment. We find that H2O and SO2 react to produce sulfur oxyanions, such as bisulfite, that as much as 30% of the SO2 can be consumed through this reaction, and that the products remain in the ice when the temperature is lowered, indicating that these reactions are irreversible. Our results suggest that thermally-induced reactions can alter the chemistry at temperatures relevant to the Icy Satellites in the Jovian system.
G Filacchione - One of the best experts on this subject based on the ideXlab platform.
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saturn s Icy Satellites investigated by cassini vims iv daytime temperature maps
Icarus, 2016Co-Authors: G Filacchione, Roger N. Clark, R. H. Brown, F Capaccioni, M Ciarniello, D P Cruikshank, P Cerroni, E Daversa, G Bellucci, Bonnie J. BurattiAbstract:Abstract The spectral position of the 3.6 µm continuum peak measured on Cassini-VIMS I/F spectra is used as a marker to infer the temperature of the regolith particles covering the surfaces of Saturn’s Icy Satellites. This feature is characterizing the crystalline water ice spectrum which is the dominant compositional endmember of the Satellites’ surfaces. Laboratory measurements indicate that the position of the 3.6 μ m peak of pure water ice is temperature-dependent, shifting towards shorter wavelengths when the sample is cooled, from about 3.65 μ m at T =123 K to about 3.55 μ m at T =88 K. A similar method was already applied to VIMS Saturn’s rings mosaics to retrieve ring particles temperature (Filacchione, G., Ciarniello, M., Capaccioni, F., et al., 2014. Icarus , 241, 45-65). We report here about the daytime temperature variations observed on the Icy Satellites as derived from three different VIMS observation types: (a) a sample of 240 disk-integrated I/F observations of Saturn’s regular Satellites collected by VIMS during years 2004–2011 with solar phase in the 20°–40° range, corresponding to late morning-early afternoon local times. This dataset is suitable to exploit the temperature variations at hemispherical scale, resulting in average temperature T T ≪88 K for Enceladus, T T =98–118 K for Dione, T =108–128 K for Rhea, T =118–128 K for Hyperion, T =128–148 and T > 168 K for Iapetus’ trailing and leading hemispheres, respectively. A typical ±5 K uncertainty is associated to the temperature retrieval. On Tethys and Dione, for which observations on both leading and trailing hemispheres are available, in average daytime temperatures higher of about 10 K on the trailing than on the leading hemisphere are inferred. (b) Satellites disk-resolved observations taken at 20–40 km pixel − 1 resolution are suitable to map daytime temperature variations across surfaces’ features, such as Enceladus’ tiger stripes and Tethys’ equatorial dark lens. These datasets allow to disentangle solar illumination conditions from temperature distribution when observing surface’s features with strong thermal contrast. (c) Daytime average maps covering large regions of the surfaces are used to compare the inferred temperature with geomorphological features (impact craters, chasmatae, equatorial radiation lenses and active areas) and albedo variations. Temperature maps are built by mining the complete VIMS dataset collected in years 2004–2009 (pre-equinox) and in 2009–2012 (post equinox) by selecting pixels with max 150 km pixel − 1 resolution. VIMS-derived temperature maps allow to identify thermal anomalies across the equatorial lens of Mimas and Tethys. A temperature T > 115K is measured above Enceladus’ Damascus and Alexandria sulci in the south pole region. VIMS has the sensitivity to follow seasonal temperature changes: on Tethys, Dione and Rhea higher temperature are measured above the south hemisphere during pre-equinox and above the north hemisphere during post-equinox epochs. The measured temperature distribution appears correlated with surface albedo features: in fact temperature increases on low albedo units located on Tethys, Dione and Rhea trailing hemispheres. The thermal anomaly region on Rhea’s Inktomi crater detected by CIRS (Howett, C. J. A., Spencer, J. R., Hurford, T., et al., 2014. Icarus , 241, 239–247) is confirmed by VIMS: this area appears colder with respect to surrounding terrains when observed at the same local solar time.
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spectroscopic classification of Icy Satellites of saturn ii identification of terrain units on rhea
Icarus, 2013Co-Authors: F. Scipioni, G Filacchione, F Capaccioni, M Ciarniello, F Tosi, K Stephan, P CerroniAbstract:Abstract Dione is one of the largest and densest Icy Satellites of Saturn. Its surface shows a marked asymmetry between its leading and trailing hemispheres, the leading side being brighter than the trailing side, which shows regions mantled by a dark veneer whose origin is likely exogenic. In order to identify different terrain units we applied the Spectral Angle Mapper (SAM) classification technique to Dione’s hyperspectral images acquired by the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini Orbiter in the infrared range (0.88–5.12 μm). On a relatively limited portion of the surface of Dione we first identified nine spectral endmembers, corresponding to as many terrain units, which mostly distinguish for water ice abundance and ice grain size. We then used these endmembers in SAM to achieve a comprehensive classification of the entire surface. The analysis of the infrared spectra returned by VIMS shows that different regions of Dione have variations in water ice bands depths, in average ice grain size, and in the concentration of contaminants, such as CO 2 and hydrocarbons, which are clearly connected to morphological and geological structures. Generally, the spectral units that classify optically dark terrains are those showing suppressed water ice bands, a finer ice grain size and a higher concentration of carbon dioxide. Conversely, spectral units labeling brighter regions have deeper water ice absorption bands, higher albedo and a smaller concentration of contaminants. We also considered VIMS cubes of the small satellite Helene (one of the two Dione’s trojan moons) and we compared its infrared spectra to those of the spectral units found on Dione. We observe that the closest match between the spectra of the two Satellites occurs for one of the youngest and freshest terrain units on Dione: the Creusa crater region.
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saturn s Icy Satellites and rings investigated by cassini vims iii radial compositional variability
Icarus, 2012Co-Authors: G Filacchione, Bonnie J. Buratti, Roger N. Clark, Jeffrey N. Cuzzi, Philip D. Nicholson, Dale P. Cruikshank, Matthew M. Hedman, F Capaccioni, M Ciarniello, Jonathan I. LunineAbstract:In the last few years Cassini–VIMS, the Visible and Infrared Mapping Spectrometer, returned to us a comprehensive view of the Saturn’s Icy Satellites and rings. After having analyzed the Satellites’ spectral properties (Filacchione, G., Capaccioni, F., McCord, T.B., Coradini, A., Cerroni, P., Bellucci, G., Tosi, F., D’Aversa, E., Formisano, V., Brown, R.H., Baines, K.H., Bibring, J.P., Buratti, B.J., Clark, R.N., Combes, M., Cruikshank, D.P., Drossart, P., Jaumann, R., Langevin, Y., Matson, D.L., Mennella, V., Nelson, R.M., Nicholson, P.D., Sicardy, B., Sotin, C., Hansen, G., Hibbitts, K., Showalter, M., Newman, S. [2007]. Icarus 186, 259–290, paper I) and their distribution across the Satellites’ hemispheres (Filacchione, G., Capaccioni, F., Clark, R.N., Cuzzi, J.N., Cruikshank, D.P., Coradini, A., Cerroni, P., Nicholson, P.D., McCord, T.B., Brown, R.H., Buratti, B.J., Tosi, F., Nelson, R.M., Jaumann, R., Stephan, K. [2010]. Icarus 206, 507–523, paper II), we proceed in this paper to investigate the radial variability of Icy Satellites (principal and minor) and main rings average spectral properties. This analysis is done by using 2264 disk-integrated observations of the Satellites and a 12 × 700 pixels-wide rings radial mosaic acquired with a spatial resolution of about 125 km/pixel. Using different VIS and IR spectral indicators, e.g. spectral slopes and band depths, we perform a comparative analysis of these data aimed to measure the distribution of water ice and red contaminant materials across Saturn’s system. The average surface regolith grain sizes are estimated with different indicators through comparison with laboratory and synthetic spectra. These measurements highlight very striking differences in the population here analyzed, which vary from the almost uncontaminated and water ice-rich surfaces of Enceladus and Calypso to the metal/organic-rich and red surfaces of Iapetus’ leading hemisphere and Phoebe. Rings spectra appear more red than the Icy Satellites in the visible range but show more intense 1.5–2.0 μm band depths. Although their orbits are close to the F-ring, Prometheus and Pandora are different in surface composition: Prometheus in fact appears very water ice-rich but at the same time very red at VIS wavelengths. These properties make it very similar to A–B ring particles while Pandora is bluer. Moving outwards, we see the effects of E ring particles, generated by Enceladus plumes, which contaminate Satellites surfaces from Mimas out to Rhea. We found some differences between Tethys lagrangian moons, Calypso being much more water ice-rich and bluer than Telesto. Among outer Satellites (Hyperion, Iapetus and Phoebe) we observe a linear trend in both water ice decrease and in reddening, Hyperion being the reddest object of the population. The correlations among spectral slopes, band depths, visual albedo and phase permit us to cluster the saturnian population in different spectral classes which are detected not only among the principal Satellites and rings but among co-orbital minor moons as well. These bodies are effectively the “connection” elements, both in term of composition and evolution, between the principal Satellites and main rings. Finally, we have applied Hapke’s theory to retrieve the best spectral fits to Saturn’s inner regular Satellites (from Mimas to Dione) using the same methodology applied previously for Rhea data discussed in Ciarniello et al. (Ciarniello, M., Capaccioni, F., Filacchione, G., Clark, R.N., Cruikshank, D.P., Cerroni, P., Coradini, A., Brown, R.H., Buratti, B.J., Tosi, F., Stephan, K. [2011]. Icarus 214, 541–555).
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saturn s Icy Satellites investigated by cassini vims ii results at the end of nominal mission
Icarus, 2010Co-Authors: G Filacchione, Roger N. Clark, Jeffrey N. Cuzzi, F Capaccioni, T. B. Mccord, D P Cruikshank, A Coradini, P Cerroni, P D Nicholson, R. H. BrownAbstract:Abstract We report the detailed analysis of the spectrophotometric properties of Saturn’s Icy Satellites as derived by full-disk observations obtained by visual and infrared mapping spectrometer (VIMS) experiment aboard Cassini. In this paper, we have extended the coverage until the end of the Cassini’s nominal mission (June 1st 2008), while a previous paper ( Filacchione, G., and 28 colleagues [2007]. Icarus 186, 259–290 , hereby referred to as Paper I) reported the preliminary results of this study. During the four years of nominal mission, VIMS has observed the entire population of Saturn’s Icy Satellites allowing us to make a comparative analysis of the VIS–NIR spectral properties of the major Satellites (Mimas, Enceladus, Tethys, Dione, Rhea, Hyperion, Iapetus) and irregular moons (Atlas, Prometheus, Pandora, Janus, Epimetheus, Telesto, Calypso, Phoebe). The results we discuss here are derived from the entire dataset available at June 2008 which consists of 1417 full-disk observations acquired from a variety of distances and inclinations from the equatorial plane, with different phase angles and hemispheric coverage. The most important spectrophotometric indicators (as defined in Paper I: I / F continua at 0.55 μm, 1.822 μm and 3.547 μm, visible spectral slopes, water and carbon dioxide bands depths and positions) are calculated for each observation in order to investigate the disk-integrated composition of the Satellites, the distribution of water ice respect to “contaminants” abundances and typical regolith grain properties. These quantities vary from the almost pure water ice surfaces of Enceladus and Calypso to the organic and carbon dioxide rich Hyperion, Iapetus and Phoebe. Janus visible colors are intermediate between these two classes having a slightly positive spectral slope. These results could help to decipher the origins and evolutionary history of the minor moons of the Saturn’s system. We introduce a polar representation of the spectrophotometric parameters as function of the solar phase angle (along radial distance) and of the effective longitude interval illuminated by the Sun and covered by VIMS during the observation (in azimuth) to better investigate the spatial distribution of the spectrophotometric quantities across the regular Satellites hemispheres. Finally, we report the observed spectral positions of the 4.26 μm band of the carbon dioxide present in the surface material of three outermost moons Hyperion, Iapetus and Phoebe.
Roger N. Clark - One of the best experts on this subject based on the ideXlab platform.
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saturn s Icy Satellites investigated by cassini vims iv daytime temperature maps
Icarus, 2016Co-Authors: G Filacchione, Roger N. Clark, R. H. Brown, F Capaccioni, M Ciarniello, D P Cruikshank, P Cerroni, E Daversa, G Bellucci, Bonnie J. BurattiAbstract:Abstract The spectral position of the 3.6 µm continuum peak measured on Cassini-VIMS I/F spectra is used as a marker to infer the temperature of the regolith particles covering the surfaces of Saturn’s Icy Satellites. This feature is characterizing the crystalline water ice spectrum which is the dominant compositional endmember of the Satellites’ surfaces. Laboratory measurements indicate that the position of the 3.6 μ m peak of pure water ice is temperature-dependent, shifting towards shorter wavelengths when the sample is cooled, from about 3.65 μ m at T =123 K to about 3.55 μ m at T =88 K. A similar method was already applied to VIMS Saturn’s rings mosaics to retrieve ring particles temperature (Filacchione, G., Ciarniello, M., Capaccioni, F., et al., 2014. Icarus , 241, 45-65). We report here about the daytime temperature variations observed on the Icy Satellites as derived from three different VIMS observation types: (a) a sample of 240 disk-integrated I/F observations of Saturn’s regular Satellites collected by VIMS during years 2004–2011 with solar phase in the 20°–40° range, corresponding to late morning-early afternoon local times. This dataset is suitable to exploit the temperature variations at hemispherical scale, resulting in average temperature T T ≪88 K for Enceladus, T T =98–118 K for Dione, T =108–128 K for Rhea, T =118–128 K for Hyperion, T =128–148 and T > 168 K for Iapetus’ trailing and leading hemispheres, respectively. A typical ±5 K uncertainty is associated to the temperature retrieval. On Tethys and Dione, for which observations on both leading and trailing hemispheres are available, in average daytime temperatures higher of about 10 K on the trailing than on the leading hemisphere are inferred. (b) Satellites disk-resolved observations taken at 20–40 km pixel − 1 resolution are suitable to map daytime temperature variations across surfaces’ features, such as Enceladus’ tiger stripes and Tethys’ equatorial dark lens. These datasets allow to disentangle solar illumination conditions from temperature distribution when observing surface’s features with strong thermal contrast. (c) Daytime average maps covering large regions of the surfaces are used to compare the inferred temperature with geomorphological features (impact craters, chasmatae, equatorial radiation lenses and active areas) and albedo variations. Temperature maps are built by mining the complete VIMS dataset collected in years 2004–2009 (pre-equinox) and in 2009–2012 (post equinox) by selecting pixels with max 150 km pixel − 1 resolution. VIMS-derived temperature maps allow to identify thermal anomalies across the equatorial lens of Mimas and Tethys. A temperature T > 115K is measured above Enceladus’ Damascus and Alexandria sulci in the south pole region. VIMS has the sensitivity to follow seasonal temperature changes: on Tethys, Dione and Rhea higher temperature are measured above the south hemisphere during pre-equinox and above the north hemisphere during post-equinox epochs. The measured temperature distribution appears correlated with surface albedo features: in fact temperature increases on low albedo units located on Tethys, Dione and Rhea trailing hemispheres. The thermal anomaly region on Rhea’s Inktomi crater detected by CIRS (Howett, C. J. A., Spencer, J. R., Hurford, T., et al., 2014. Icarus , 241, 239–247) is confirmed by VIMS: this area appears colder with respect to surrounding terrains when observed at the same local solar time.
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saturn s Icy Satellites and rings investigated by cassini vims iii radial compositional variability
Icarus, 2012Co-Authors: G Filacchione, Bonnie J. Buratti, Roger N. Clark, Jeffrey N. Cuzzi, Philip D. Nicholson, Dale P. Cruikshank, Matthew M. Hedman, F Capaccioni, M Ciarniello, Jonathan I. LunineAbstract:In the last few years Cassini–VIMS, the Visible and Infrared Mapping Spectrometer, returned to us a comprehensive view of the Saturn’s Icy Satellites and rings. After having analyzed the Satellites’ spectral properties (Filacchione, G., Capaccioni, F., McCord, T.B., Coradini, A., Cerroni, P., Bellucci, G., Tosi, F., D’Aversa, E., Formisano, V., Brown, R.H., Baines, K.H., Bibring, J.P., Buratti, B.J., Clark, R.N., Combes, M., Cruikshank, D.P., Drossart, P., Jaumann, R., Langevin, Y., Matson, D.L., Mennella, V., Nelson, R.M., Nicholson, P.D., Sicardy, B., Sotin, C., Hansen, G., Hibbitts, K., Showalter, M., Newman, S. [2007]. Icarus 186, 259–290, paper I) and their distribution across the Satellites’ hemispheres (Filacchione, G., Capaccioni, F., Clark, R.N., Cuzzi, J.N., Cruikshank, D.P., Coradini, A., Cerroni, P., Nicholson, P.D., McCord, T.B., Brown, R.H., Buratti, B.J., Tosi, F., Nelson, R.M., Jaumann, R., Stephan, K. [2010]. Icarus 206, 507–523, paper II), we proceed in this paper to investigate the radial variability of Icy Satellites (principal and minor) and main rings average spectral properties. This analysis is done by using 2264 disk-integrated observations of the Satellites and a 12 × 700 pixels-wide rings radial mosaic acquired with a spatial resolution of about 125 km/pixel. Using different VIS and IR spectral indicators, e.g. spectral slopes and band depths, we perform a comparative analysis of these data aimed to measure the distribution of water ice and red contaminant materials across Saturn’s system. The average surface regolith grain sizes are estimated with different indicators through comparison with laboratory and synthetic spectra. These measurements highlight very striking differences in the population here analyzed, which vary from the almost uncontaminated and water ice-rich surfaces of Enceladus and Calypso to the metal/organic-rich and red surfaces of Iapetus’ leading hemisphere and Phoebe. Rings spectra appear more red than the Icy Satellites in the visible range but show more intense 1.5–2.0 μm band depths. Although their orbits are close to the F-ring, Prometheus and Pandora are different in surface composition: Prometheus in fact appears very water ice-rich but at the same time very red at VIS wavelengths. These properties make it very similar to A–B ring particles while Pandora is bluer. Moving outwards, we see the effects of E ring particles, generated by Enceladus plumes, which contaminate Satellites surfaces from Mimas out to Rhea. We found some differences between Tethys lagrangian moons, Calypso being much more water ice-rich and bluer than Telesto. Among outer Satellites (Hyperion, Iapetus and Phoebe) we observe a linear trend in both water ice decrease and in reddening, Hyperion being the reddest object of the population. The correlations among spectral slopes, band depths, visual albedo and phase permit us to cluster the saturnian population in different spectral classes which are detected not only among the principal Satellites and rings but among co-orbital minor moons as well. These bodies are effectively the “connection” elements, both in term of composition and evolution, between the principal Satellites and main rings. Finally, we have applied Hapke’s theory to retrieve the best spectral fits to Saturn’s inner regular Satellites (from Mimas to Dione) using the same methodology applied previously for Rhea data discussed in Ciarniello et al. (Ciarniello, M., Capaccioni, F., Filacchione, G., Clark, R.N., Cruikshank, D.P., Cerroni, P., Coradini, A., Brown, R.H., Buratti, B.J., Tosi, F., Stephan, K. [2011]. Icarus 214, 541–555).
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Saturn’s Icy Satellites and rings investigated by Cassini–VIMS: III – Radial compositional variability
Icarus, 2012Co-Authors: Gianrico Filacchione, Bonnie J. Buratti, F. Capaccioni, Roger N. Clark, Mauro Ciarniello, Jeffrey N. Cuzzi, Philip D. Nicholson, Dale P. Cruikshank, Matthew M. Hedman, Jonathan I. LunineAbstract:In the last few years Cassini–VIMS, the Visible and Infrared Mapping Spectrometer, returned to us a comprehensive view of the Saturn’s Icy Satellites and rings. After having analyzed the Satellites’ spectral properties (Filacchione, G., Capaccioni, F., McCord, T.B., Coradini, A., Cerroni, P., Bellucci, G., Tosi, F., D’Aversa, E., Formisano, V., Brown, R.H., Baines, K.H., Bibring, J.P., Buratti, B.J., Clark, R.N., Combes, M., Cruikshank, D.P., Drossart, P., Jaumann, R., Langevin, Y., Matson, D.L., Mennella, V., Nelson, R.M., Nicholson, P.D., Sicardy, B., Sotin, C., Hansen, G., Hibbitts, K., Showalter, M., Newman, S. [2007]. Icarus 186, 259–290, paper I) and their distribution across the Satellites’ hemispheres (Filacchione, G., Capaccioni, F., Clark, R.N., Cuzzi, J.N., Cruikshank, D.P., Coradini, A., Cerroni, P., Nicholson, P.D., McCord, T.B., Brown, R.H., Buratti, B.J., Tosi, F., Nelson, R.M., Jaumann, R., Stephan, K. [2010]. Icarus 206, 507–523, paper II), we proceed in this paper to investigate the radial variability of Icy Satellites (principal and minor) and main rings average spectral properties. This analysis is done by using 2264 disk-integrated observations of the Satellites and a 12 × 700 pixels-wide rings radial mosaic acquired with a spatial resolution of about 125 km/pixel. Using different VIS and IR spectral indicators, e.g. spectral slopes and band depths, we perform a comparative analysis of these data aimed to measure the distribution of water ice and red contaminant materials across Saturn’s system. The average surface regolith grain sizes are estimated with different indicators through comparison with laboratory and synthetic spectra. These measurements highlight very striking differences in the population here analyzed, which vary from the almost uncontaminated and water ice-rich surfaces of Enceladus and Calypso to the metal/organic-rich and red surfaces of Iapetus’ leading hemisphere and Phoebe. Rings spectra appear more red than the Icy Satellites in the visible range but show more intense 1.5–2.0 μm band depths. Although their orbits are close to the F-ring, Prometheus and Pandora are different in surface composition: Prometheus in fact appears very water ice-rich but at the same time very red at VIS wavelengths. These properties make it very similar to A–B ring particles while Pandora is bluer. Moving outwards, we see the effects of E ring particles, generated by Enceladus plumes, which contaminate Satellites surfaces from Mimas out to Rhea. We found some differences between Tethys lagrangian moons, Calypso being much more water ice-rich and bluer than Telesto. Among outer Satellites (Hyperion, Iapetus and Phoebe) we observe a linear trend in both water ice decrease and in reddening, Hyperion being the reddest object of the population. The correlations among spectral slopes, band depths, visual albedo and phase permit us to cluster the saturnian population in different spectral classes which are detected not only among the principal Satellites and rings but among co-orbital minor moons as well. These bodies are effectively the “connection” elements, both in term of composition and evolution, between the principal Satellites and main rings. Finally, we have applied Hapke’s theory to retrieve the best spectral fits to Saturn’s inner regular Satellites (from Mimas to Dione) using the same methodology applied previously for Rhea data discussed in Ciarniello et al. (Ciarniello, M., Capaccioni, F., Filacchione, G., Clark, R.N., Cruikshank, D.P., Cerroni, P., Coradini, A., Brown, R.H., Buratti, B.J., Tosi, F., Stephan, K. [2011]. Icarus 214, 541–555).
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saturn s Icy Satellites investigated by cassini vims ii results at the end of nominal mission
Icarus, 2010Co-Authors: G Filacchione, Roger N. Clark, Jeffrey N. Cuzzi, F Capaccioni, T. B. Mccord, D P Cruikshank, A Coradini, P Cerroni, P D Nicholson, R. H. BrownAbstract:Abstract We report the detailed analysis of the spectrophotometric properties of Saturn’s Icy Satellites as derived by full-disk observations obtained by visual and infrared mapping spectrometer (VIMS) experiment aboard Cassini. In this paper, we have extended the coverage until the end of the Cassini’s nominal mission (June 1st 2008), while a previous paper ( Filacchione, G., and 28 colleagues [2007]. Icarus 186, 259–290 , hereby referred to as Paper I) reported the preliminary results of this study. During the four years of nominal mission, VIMS has observed the entire population of Saturn’s Icy Satellites allowing us to make a comparative analysis of the VIS–NIR spectral properties of the major Satellites (Mimas, Enceladus, Tethys, Dione, Rhea, Hyperion, Iapetus) and irregular moons (Atlas, Prometheus, Pandora, Janus, Epimetheus, Telesto, Calypso, Phoebe). The results we discuss here are derived from the entire dataset available at June 2008 which consists of 1417 full-disk observations acquired from a variety of distances and inclinations from the equatorial plane, with different phase angles and hemispheric coverage. The most important spectrophotometric indicators (as defined in Paper I: I / F continua at 0.55 μm, 1.822 μm and 3.547 μm, visible spectral slopes, water and carbon dioxide bands depths and positions) are calculated for each observation in order to investigate the disk-integrated composition of the Satellites, the distribution of water ice respect to “contaminants” abundances and typical regolith grain properties. These quantities vary from the almost pure water ice surfaces of Enceladus and Calypso to the organic and carbon dioxide rich Hyperion, Iapetus and Phoebe. Janus visible colors are intermediate between these two classes having a slightly positive spectral slope. These results could help to decipher the origins and evolutionary history of the minor moons of the Saturn’s system. We introduce a polar representation of the spectrophotometric parameters as function of the solar phase angle (along radial distance) and of the effective longitude interval illuminated by the Sun and covered by VIMS during the observation (in azimuth) to better investigate the spatial distribution of the spectrophotometric quantities across the regular Satellites hemispheres. Finally, we report the observed spectral positions of the 4.26 μm band of the carbon dioxide present in the surface material of three outermost moons Hyperion, Iapetus and Phoebe.
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Saturn’s Icy Satellites investigated by Cassini–VIMS: II. Results at the end of nominal mission
Icarus, 2010Co-Authors: Gianrico Filacchione, Angioletta Coradini, F. Capaccioni, Priscilla Cerroni, Roger N. Clark, Jeffrey N. Cuzzi, Philip D. Nicholson, Dale P. Cruikshank, T. B. Mccord, Robert H. BrownAbstract:Abstract We report the detailed analysis of the spectrophotometric properties of Saturn’s Icy Satellites as derived by full-disk observations obtained by visual and infrared mapping spectrometer (VIMS) experiment aboard Cassini. In this paper, we have extended the coverage until the end of the Cassini’s nominal mission (June 1st 2008), while a previous paper ( Filacchione, G., and 28 colleagues [2007]. Icarus 186, 259–290 , hereby referred to as Paper I) reported the preliminary results of this study. During the four years of nominal mission, VIMS has observed the entire population of Saturn’s Icy Satellites allowing us to make a comparative analysis of the VIS–NIR spectral properties of the major Satellites (Mimas, Enceladus, Tethys, Dione, Rhea, Hyperion, Iapetus) and irregular moons (Atlas, Prometheus, Pandora, Janus, Epimetheus, Telesto, Calypso, Phoebe). The results we discuss here are derived from the entire dataset available at June 2008 which consists of 1417 full-disk observations acquired from a variety of distances and inclinations from the equatorial plane, with different phase angles and hemispheric coverage. The most important spectrophotometric indicators (as defined in Paper I: I / F continua at 0.55 μm, 1.822 μm and 3.547 μm, visible spectral slopes, water and carbon dioxide bands depths and positions) are calculated for each observation in order to investigate the disk-integrated composition of the Satellites, the distribution of water ice respect to “contaminants” abundances and typical regolith grain properties. These quantities vary from the almost pure water ice surfaces of Enceladus and Calypso to the organic and carbon dioxide rich Hyperion, Iapetus and Phoebe. Janus visible colors are intermediate between these two classes having a slightly positive spectral slope. These results could help to decipher the origins and evolutionary history of the minor moons of the Saturn’s system. We introduce a polar representation of the spectrophotometric parameters as function of the solar phase angle (along radial distance) and of the effective longitude interval illuminated by the Sun and covered by VIMS during the observation (in azimuth) to better investigate the spatial distribution of the spectrophotometric quantities across the regular Satellites hemispheres. Finally, we report the observed spectral positions of the 4.26 μm band of the carbon dioxide present in the surface material of three outermost moons Hyperion, Iapetus and Phoebe.
Jacek Leliwa-kopystynski - One of the best experts on this subject based on the ideXlab platform.
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Longitudinal asymmetry of craters' density distributions on the Icy Satellites
Planetary and Space Science, 2012Co-Authors: Jacek Leliwa-kopystynski, Marcin Banaszek, Ireneusz WłodarczykAbstract:Abstract Crater's density distribution versus satellitographical longitude was searched for seven Icy Satellites: two of Jupiter (Ganymede and Callisto) and five of Saturn (Mimas, Tethys, Dione, Rhea and Iapetus). Craters were classified according to their size. Four bins of the craters' diameter were used. Density distributions were found in the longitudinal sectors of the near-equatorial stripes that circumscribe the Satellites. The size distributions (R-plots) were done independently for each of the eight longitudinal sectors of the Satellites. Searching for the leading/trailing (apex/antapex) and the near-side/far-side asymmetry was done. It was found that the crater density is longitudinally asymmetric for all seven Satellites being studied. However, the apex–antapex asymmetry is much less pronounced than predicted by theory of Zahnle et al. (2003) , for impacts on the Satellites by ecliptic comets. We conclude that the impact craters observed on the considered Satellites are mostly originated from planetocentric swarm of debris. In that case longitudinal asymmetry is not expected, as stated by Horedt and Neukum, 1984a , Horedt and Neukum, 1984b . However, cratering longitudinal asymmetry that we observe for Mimas perfectly agrees with calculations of Alvarellos et al. (2005) . It is very likely that important part of craters on Mimas were formed due to impacts of ejecta originated from crater Herschel.
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Density distribution in medium-sized Icy Satellites of giant planets
Earth Planets and Space, 2007Co-Authors: Leszek Czechowski, Jacek Leliwa-kopystynskiAbstract:We discuss processes that determine the distribution of density in the medium-sized Icy Satellites (MIS). Gravitational differentiation, porosity and phase transitions lead to a spherical distribution, while thermal convection, large impacts and tidal deformation can result in a non-spherical distribution. According to our previous research, convective patterns in MIS can consist of one or two convective cells for radiogenic and tidal heating. The shift of the center of mass ΔrCM and the ratio of moments of inertia IZ/IXY are calculated using a numerical model of convection. A new dimensionless number C is introduced to describe the deformation of the surface. We found that ΔrCM can reach ≈0.5% of the satellite radius for the one-cell pattern. With the two-cell pattern the moment of inertia, IZ, can be reduced by ≈0.4%. The impact cratering could be one cause of significant changes in ΔrCM and IZ /IXY but only for the smallest of the MIS. Tidal deformation could result in the enhancement of mass redistribution caused by other mechanisms.
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Convection driven by tidal and radiogenic heating in medium size Icy Satellites
Planetary and Space Science, 2005Co-Authors: Leszek Czechowski, Jacek Leliwa-kopystynskiAbstract:Abstract Convection is one of the most important processes responsible for the formation of the surface features on many planetary bodies. Observations of some Icy Satellites indicate that the Satellites’ surfaces are modified due to the internally driven tectonic activity. The tidal heating could be an important source of energy responsible for such internal activity. This suggestion is supported by the correlation of the tidal parameter ψ and tectonic features. Consequently, the tidal and the radiogenic heat sources seem to be of primary importance for the medium size Icy Satellites. Our research deals with convection in a non-differentiated body. The convection is a results of both uniform radiogenic heating and non-uniform and non-spherically symmetric tidal heating. To investigate the problem a 3D model of convection is developed based on the Navier–Stokes equation, the equation of thermal conductivity, the equation of continuity, and the equation of state. The 3D formulae for the tidal heat generation based on the results of Peale and Cassen [1978. Icarus 36, 245–269] and others are used in the model. To measure the relative importance of radiogenic heating versus tidal heating a dimensionless number C t is introduced. The systematic investigation of a steady-state convection is performed for different values of the Rayleigh number and for the full range of C t . The results indicate that for low and moderate value of the Rayleigh number, convection pattern driven by the tidal heating and by the radioactivity in the medium size Icy Satellites consists of one cell or of two cells. For C t > 0 the critical value of Rayleigh number Ra cr = 0 . The one-cell pattern is specific for low Rayleigh numbers but it could be observed for the full range of number C t . It means that the pattern of convection does not fully follow the pattern of heating. This rather unexpected result could be of great importance for the final stage of convection. All patterns of tidally driven convection are oriented with respect to the direction to the planet. For two-cell patterns the regions of downward motion are situated in the centers of the near and far sides of the satellite, respectively.
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Solid state convection in the Icy Satellites: numerical results
Advances in Space Research, 2002Co-Authors: Leszek Czechowski, Jacek Leliwa-kopystynskiAbstract:Abstract Solid state convection in the mantle of Icy Satellites of giant planets is investigated using numerical models. We consider differentiated and non-differentiated Satellites with both free (that is no horizontal stresses) and rigid (that is zero velocity) boundary conditions at the body surface. Internal heating originates from long lived radioactive elements uniformly distributed within rocky component of Satellites (with initial chondritic concentration). Two modes of internal heating by radioactive sources are considered: uniform distribution of radioactive elements within undifferentiated bodies and heating of the Icy mantle by heat flux from the rocky core. The calculations were performed for the range of Rayleigh number from 10 000 to 300 000. It corresponds to the medium size Icy Satellites in radii from the range 200 – 800 km. We found that convection velocity of the order of 1 mm yr −1 is typical for considered bodies. This is at least one order of magnitude less than the velocity in the Earth's mantle but even such slow convection could be an important factor changing global tectonic activity, asymmetry of hemispheres, gravitational field and shape of the Satellites.
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Solid state convection in the Icy Satellites: discussion of its possibility
Advances in Space Research, 2002Co-Authors: Leszek Czechowski, Jacek Leliwa-kopystynskiAbstract:Abstract Surface features of Enceladus, Tethys, Dione, Iapetus, Miranda, Ariel, and Titania indicate that these Satellites, with radii from the range 252–879 km, are highly or at least moderately modified due to internal tectonic activity. Detailed studies of known surfaces show that Enceladus is probably still geologically active at present while Tethys, Dione, Miranda, Ariel, and Titania were active in the recent past. Convection is one of the processes responsible for the evolution of the bodies of Solar System, including the evolution of Icy Satellites. We focus on studying the possibility of convection within the medium sized Icy Satellites. Thermally driven convection of solid satellite material as potential cause of surface evolution is considered for two cases: non-differentiated Icy-mineral Satellites and differentiated Satellites with Icy mantle and rocky core. Discussion of the parameters of Icy/rocky mixture indicates that the Rayleigh number is higher than critical value for onset of convection.
Bonnie J. Buratti - One of the best experts on this subject based on the ideXlab platform.
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saturn s Icy Satellites investigated by cassini vims iv daytime temperature maps
Icarus, 2016Co-Authors: G Filacchione, Roger N. Clark, R. H. Brown, F Capaccioni, M Ciarniello, D P Cruikshank, P Cerroni, E Daversa, G Bellucci, Bonnie J. BurattiAbstract:Abstract The spectral position of the 3.6 µm continuum peak measured on Cassini-VIMS I/F spectra is used as a marker to infer the temperature of the regolith particles covering the surfaces of Saturn’s Icy Satellites. This feature is characterizing the crystalline water ice spectrum which is the dominant compositional endmember of the Satellites’ surfaces. Laboratory measurements indicate that the position of the 3.6 μ m peak of pure water ice is temperature-dependent, shifting towards shorter wavelengths when the sample is cooled, from about 3.65 μ m at T =123 K to about 3.55 μ m at T =88 K. A similar method was already applied to VIMS Saturn’s rings mosaics to retrieve ring particles temperature (Filacchione, G., Ciarniello, M., Capaccioni, F., et al., 2014. Icarus , 241, 45-65). We report here about the daytime temperature variations observed on the Icy Satellites as derived from three different VIMS observation types: (a) a sample of 240 disk-integrated I/F observations of Saturn’s regular Satellites collected by VIMS during years 2004–2011 with solar phase in the 20°–40° range, corresponding to late morning-early afternoon local times. This dataset is suitable to exploit the temperature variations at hemispherical scale, resulting in average temperature T T ≪88 K for Enceladus, T T =98–118 K for Dione, T =108–128 K for Rhea, T =118–128 K for Hyperion, T =128–148 and T > 168 K for Iapetus’ trailing and leading hemispheres, respectively. A typical ±5 K uncertainty is associated to the temperature retrieval. On Tethys and Dione, for which observations on both leading and trailing hemispheres are available, in average daytime temperatures higher of about 10 K on the trailing than on the leading hemisphere are inferred. (b) Satellites disk-resolved observations taken at 20–40 km pixel − 1 resolution are suitable to map daytime temperature variations across surfaces’ features, such as Enceladus’ tiger stripes and Tethys’ equatorial dark lens. These datasets allow to disentangle solar illumination conditions from temperature distribution when observing surface’s features with strong thermal contrast. (c) Daytime average maps covering large regions of the surfaces are used to compare the inferred temperature with geomorphological features (impact craters, chasmatae, equatorial radiation lenses and active areas) and albedo variations. Temperature maps are built by mining the complete VIMS dataset collected in years 2004–2009 (pre-equinox) and in 2009–2012 (post equinox) by selecting pixels with max 150 km pixel − 1 resolution. VIMS-derived temperature maps allow to identify thermal anomalies across the equatorial lens of Mimas and Tethys. A temperature T > 115K is measured above Enceladus’ Damascus and Alexandria sulci in the south pole region. VIMS has the sensitivity to follow seasonal temperature changes: on Tethys, Dione and Rhea higher temperature are measured above the south hemisphere during pre-equinox and above the north hemisphere during post-equinox epochs. The measured temperature distribution appears correlated with surface albedo features: in fact temperature increases on low albedo units located on Tethys, Dione and Rhea trailing hemispheres. The thermal anomaly region on Rhea’s Inktomi crater detected by CIRS (Howett, C. J. A., Spencer, J. R., Hurford, T., et al., 2014. Icarus , 241, 239–247) is confirmed by VIMS: this area appears colder with respect to surrounding terrains when observed at the same local solar time.
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saturn s Icy Satellites and rings investigated by cassini vims iii radial compositional variability
Icarus, 2012Co-Authors: G Filacchione, Bonnie J. Buratti, Roger N. Clark, Jeffrey N. Cuzzi, Philip D. Nicholson, Dale P. Cruikshank, Matthew M. Hedman, F Capaccioni, M Ciarniello, Jonathan I. LunineAbstract:In the last few years Cassini–VIMS, the Visible and Infrared Mapping Spectrometer, returned to us a comprehensive view of the Saturn’s Icy Satellites and rings. After having analyzed the Satellites’ spectral properties (Filacchione, G., Capaccioni, F., McCord, T.B., Coradini, A., Cerroni, P., Bellucci, G., Tosi, F., D’Aversa, E., Formisano, V., Brown, R.H., Baines, K.H., Bibring, J.P., Buratti, B.J., Clark, R.N., Combes, M., Cruikshank, D.P., Drossart, P., Jaumann, R., Langevin, Y., Matson, D.L., Mennella, V., Nelson, R.M., Nicholson, P.D., Sicardy, B., Sotin, C., Hansen, G., Hibbitts, K., Showalter, M., Newman, S. [2007]. Icarus 186, 259–290, paper I) and their distribution across the Satellites’ hemispheres (Filacchione, G., Capaccioni, F., Clark, R.N., Cuzzi, J.N., Cruikshank, D.P., Coradini, A., Cerroni, P., Nicholson, P.D., McCord, T.B., Brown, R.H., Buratti, B.J., Tosi, F., Nelson, R.M., Jaumann, R., Stephan, K. [2010]. Icarus 206, 507–523, paper II), we proceed in this paper to investigate the radial variability of Icy Satellites (principal and minor) and main rings average spectral properties. This analysis is done by using 2264 disk-integrated observations of the Satellites and a 12 × 700 pixels-wide rings radial mosaic acquired with a spatial resolution of about 125 km/pixel. Using different VIS and IR spectral indicators, e.g. spectral slopes and band depths, we perform a comparative analysis of these data aimed to measure the distribution of water ice and red contaminant materials across Saturn’s system. The average surface regolith grain sizes are estimated with different indicators through comparison with laboratory and synthetic spectra. These measurements highlight very striking differences in the population here analyzed, which vary from the almost uncontaminated and water ice-rich surfaces of Enceladus and Calypso to the metal/organic-rich and red surfaces of Iapetus’ leading hemisphere and Phoebe. Rings spectra appear more red than the Icy Satellites in the visible range but show more intense 1.5–2.0 μm band depths. Although their orbits are close to the F-ring, Prometheus and Pandora are different in surface composition: Prometheus in fact appears very water ice-rich but at the same time very red at VIS wavelengths. These properties make it very similar to A–B ring particles while Pandora is bluer. Moving outwards, we see the effects of E ring particles, generated by Enceladus plumes, which contaminate Satellites surfaces from Mimas out to Rhea. We found some differences between Tethys lagrangian moons, Calypso being much more water ice-rich and bluer than Telesto. Among outer Satellites (Hyperion, Iapetus and Phoebe) we observe a linear trend in both water ice decrease and in reddening, Hyperion being the reddest object of the population. The correlations among spectral slopes, band depths, visual albedo and phase permit us to cluster the saturnian population in different spectral classes which are detected not only among the principal Satellites and rings but among co-orbital minor moons as well. These bodies are effectively the “connection” elements, both in term of composition and evolution, between the principal Satellites and main rings. Finally, we have applied Hapke’s theory to retrieve the best spectral fits to Saturn’s inner regular Satellites (from Mimas to Dione) using the same methodology applied previously for Rhea data discussed in Ciarniello et al. (Ciarniello, M., Capaccioni, F., Filacchione, G., Clark, R.N., Cruikshank, D.P., Cerroni, P., Coradini, A., Brown, R.H., Buratti, B.J., Tosi, F., Stephan, K. [2011]. Icarus 214, 541–555).
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Saturn’s Icy Satellites and rings investigated by Cassini–VIMS: III – Radial compositional variability
Icarus, 2012Co-Authors: Gianrico Filacchione, Bonnie J. Buratti, F. Capaccioni, Roger N. Clark, Mauro Ciarniello, Jeffrey N. Cuzzi, Philip D. Nicholson, Dale P. Cruikshank, Matthew M. Hedman, Jonathan I. LunineAbstract:In the last few years Cassini–VIMS, the Visible and Infrared Mapping Spectrometer, returned to us a comprehensive view of the Saturn’s Icy Satellites and rings. After having analyzed the Satellites’ spectral properties (Filacchione, G., Capaccioni, F., McCord, T.B., Coradini, A., Cerroni, P., Bellucci, G., Tosi, F., D’Aversa, E., Formisano, V., Brown, R.H., Baines, K.H., Bibring, J.P., Buratti, B.J., Clark, R.N., Combes, M., Cruikshank, D.P., Drossart, P., Jaumann, R., Langevin, Y., Matson, D.L., Mennella, V., Nelson, R.M., Nicholson, P.D., Sicardy, B., Sotin, C., Hansen, G., Hibbitts, K., Showalter, M., Newman, S. [2007]. Icarus 186, 259–290, paper I) and their distribution across the Satellites’ hemispheres (Filacchione, G., Capaccioni, F., Clark, R.N., Cuzzi, J.N., Cruikshank, D.P., Coradini, A., Cerroni, P., Nicholson, P.D., McCord, T.B., Brown, R.H., Buratti, B.J., Tosi, F., Nelson, R.M., Jaumann, R., Stephan, K. [2010]. Icarus 206, 507–523, paper II), we proceed in this paper to investigate the radial variability of Icy Satellites (principal and minor) and main rings average spectral properties. This analysis is done by using 2264 disk-integrated observations of the Satellites and a 12 × 700 pixels-wide rings radial mosaic acquired with a spatial resolution of about 125 km/pixel. Using different VIS and IR spectral indicators, e.g. spectral slopes and band depths, we perform a comparative analysis of these data aimed to measure the distribution of water ice and red contaminant materials across Saturn’s system. The average surface regolith grain sizes are estimated with different indicators through comparison with laboratory and synthetic spectra. These measurements highlight very striking differences in the population here analyzed, which vary from the almost uncontaminated and water ice-rich surfaces of Enceladus and Calypso to the metal/organic-rich and red surfaces of Iapetus’ leading hemisphere and Phoebe. Rings spectra appear more red than the Icy Satellites in the visible range but show more intense 1.5–2.0 μm band depths. Although their orbits are close to the F-ring, Prometheus and Pandora are different in surface composition: Prometheus in fact appears very water ice-rich but at the same time very red at VIS wavelengths. These properties make it very similar to A–B ring particles while Pandora is bluer. Moving outwards, we see the effects of E ring particles, generated by Enceladus plumes, which contaminate Satellites surfaces from Mimas out to Rhea. We found some differences between Tethys lagrangian moons, Calypso being much more water ice-rich and bluer than Telesto. Among outer Satellites (Hyperion, Iapetus and Phoebe) we observe a linear trend in both water ice decrease and in reddening, Hyperion being the reddest object of the population. The correlations among spectral slopes, band depths, visual albedo and phase permit us to cluster the saturnian population in different spectral classes which are detected not only among the principal Satellites and rings but among co-orbital minor moons as well. These bodies are effectively the “connection” elements, both in term of composition and evolution, between the principal Satellites and main rings. Finally, we have applied Hapke’s theory to retrieve the best spectral fits to Saturn’s inner regular Satellites (from Mimas to Dione) using the same methodology applied previously for Rhea data discussed in Ciarniello et al. (Ciarniello, M., Capaccioni, F., Filacchione, G., Clark, R.N., Cruikshank, D.P., Cerroni, P., Coradini, A., Brown, R.H., Buratti, B.J., Tosi, F., Stephan, K. [2011]. Icarus 214, 541–555).
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Icy Satellites: Geological Evolution and Surface Processes
Saturn from Cassini-Huygens, 2009Co-Authors: Ralf Jaumann, Paul M. Schenk, Francis Nimmo, Bonnie J. Buratti, Amanda R. Hendrix, Roger N. Clark, Tilmann Denk, Jeffrey M. Moore, Steve J. Ostro, Ralf SramaAbstract:The sizes of the Saturnian Icy Satellites range from ~ 1;500 km in diameter (Rhea) to ~20km (Calypso), and even smaller ‘rocks’ of only a kilometer in diameter are common in the system. All these bodies exhibit remarkable, unique features and unexpected diversity. In this chapter, we will mostly focus on the ‘medium-sized Icy objects’ Mimas, Tethys, Dione, Rhea, Iapetus, Phoebe and Hyperion, and consider small objects only where appropriate, whereas Titan and Enceladus will be described in separate chapters. Mimas and Tethys show impact craters caused by bodies that were almost large enough to break them apart. Iapetus is unique in the Saturnian system because of its extreme global brightness dichotomy. Tectonic activity varies widely — from inactive Mimas through extensional terrains on Rhea and Dione to the current cryovolcanic eruptions on Enceladus — and is not necessarily correlated with predicted tidal stresses. Likely sources of stress include impacts, despinning, reorientation and volume changes. Accretion of dark material originating from outside the Saturnian system may explain the surface contamination that prevails in the whole satellite system, while coating by Saturn's E-ring particles brightens the inner Satellites.
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The Saturn system's Icy Satellites: New results from Cassini
Icarus, 2008Co-Authors: Rosaly M. C. Lopes, Bonnie J. Buratti, Amanda R. HendrixAbstract:Cassini-Huygens is a multidisciplinary, international planetary mission consisting of an orbiting spacecraft and a probe. The Huygens probe successfully landed on Titan's surface on January 14, 2005, while the orbiter has performed observations of Saturn, its rings, Satellites, and magnetosphere since it entered orbit around Saturn on July 1, 2004. The Cassini mission has been prolific in its scientific discoveries about the Saturn system. In this special section, we present new mission results with a focus on the 'Icy Satellites,' which we define as all Saturn's moons with the exception of Titan. The results included in this section have come out of the Cassini SOST--Satellites Orbiter Science Team--a multi-instrument and multidiscipline group that works together to better understand the Icy Satellites and their interactions with Saturn and its rings. Other papers included in this issue present ground-based observations and interior modeling of these Icy moons.
