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G. Filacchione,
F. Capaccioni,
T.B. McCord,
A. Coradini,
P. Cerroni,
G. Bellucci,
F. Tosi,
E. D'Aversa,
V. Formisano,
R.H. Brown, [......],
D.L. Matson,
V. Mennella,
R.M. Nelson,
P.D. Nicholson,
B. Sicardy,
C. Sotin,
G. Hansen,
K. Hibbitts, M. Showalter,
S. Newman
[show abstract]
[hide abstract]
ABSTRACT: Abstract:
Saturn's icy satellites are among the main scientific objectives of the Cassini-VIMS (Visual and Infrared Mapping Spectrometer) experiment. This paper contains a first systematic and comparative analysis of the full-disk spectral properties of Dione, Enceladus, Epimetheus, Hyperion, Iapetus, Mimas, Phoebe, Rhea and Tethys as observed by VIMS from July 2004 to June 2005. The disk integrated properties (350–5100 nm reflectance spectra and phase curves at 550–2232 nm) and images of satellites are reported and discussed in detail together with the observed geometry. In general, the spectra in the visible spectral range are almost featureless and can be classified according to the spectral slopes: from the bluish Enceladus and Phoebe to the redder Iapetus, Hyperion and Epimetheus. In the 1000–1300 nm range the spectra of Enceladus, Tethys, Mimas and Rhea are characterized by a negative slope, consistent with a surface largely dominated by water ice, while the spectra of Iapetus, Hyperion and Phoebe show a considerable reddening pointing out the relevant role played by darkening materials present on the surface. In between these two classes are Dione and Epimetheus, which have a flat spectrum in this range. The main absorption bands identified in the infrared are the 1520, 2020, 3000 nm H2O/OH bands (for all satellites), although Iapetus dark terrains show mostly a deep 3000 nm band while the 1520 and 2020 nm bands are very faint. In this spectral range, the Iapetus spectrum is characterized by a strong reddening. The CO2 band at 4260 nm and the Fresnel ice peak around 3100 nm are evident only on Hyperion, Phoebe and Iapetus. The phase curves at 550 and at 2232 nm are reported for all the available observations in the 0°–144° range; Rhea shows an opposition surge at visible wavelengths in the 0.5°–1.17° interval. The improvement on the retrieval of the full-disk reflectance spectra can be appreciated by a direct comparison with ground-based telescopic data available from literature. Finally, data processing strategies and recent upgrades introduced in the VIMS-V calibration pipeline (flat-field and destriping–despiking algorithm) are discussed in appendices.
Icarus: International Journal of Solar System Studies.
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R.H. Brown,
K.H. Baines,
G. Bellucci,
J.-P. Bibring,
B.J. Buratti,
F. Capaccioni,
P. Cerroni,
R.N. Clark,
A. Coradini,
D.P. Cruikshank, [......],
R.M. Nelson,
P.D. Nicholson,
B. Sicardy,
C. Sotin,
S. Amici,
M.C. Chamberlain,
G. Filacchione,
G. Hansen,
K. Hibbitts, M. Showalter
[show abstract]
[hide abstract]
ABSTRACT: The Cassini Visual and Infrared Mapping Spectrometer (VIMS) is an imaging spectrometer covering the wavelength range 0.3-5.2 ¼m in 352 spectral channels, with a nominal instantaneous field of view of 0.5 mrad. The Cassini flyby of Jupiter represented a unique opportunity to accomplish two important goals: scientific observations of the jovian system and functional tests of the VIMS instrument under conditions similar to those expected to obtain during Cassini's 4-year tour of the saturnian system. Results acquired over a complete range of visual to near-infrared wavelengths from 0.3 to 5.2 ¼m are presented. First detections include methane fluorescence on Jupiter, a surprisingly high opposition surge on Europa, the first visual-near-IR spectra of Himalia and Jupiter's optically-thin ring system, and the first near-infrared observations of the rings over an extensive range of phase angles (0-120°). Similarities in the center-to-limb profiles of H+3 and CH4 emissions indicate that the H+3 ionospheric density is solar-controlled outside of the auroral regions. The existence of jovian NH3 absorption at 0.93 ¼m is confirmed. Himalia has a slightly reddish spectrum, an apparent absorption near 3 ¼m, and a geometric albedo of /0.06+/-0.01 at 2.2 ¼m (assuming an 85-km radius). If the 3-¼m feature in Himalia's spectrum is eventually confirmed, it would be suggestive of the presence of water in some form, either free, bound, or incorporated in layer-lattice silicates. Finally, a mean ring-particle radius of 10 ¼m is found to be consistent with Mie-scattering models fit to VIMS near-infrared observations acquired over 0-120° phase angle.
Icarus. 146(2003-2):461-470.
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V. Formisano,
E. D'Aversa,
G. Bellucci,
K.H. Baines,
J.P. Bibring,
R.H. Brown,
B.J. Buratti,
F. Capaccioni,
P. Cerroni,
R.N. Clark, [......],
V. Mennella,
R.M. Nelson,
P.D. Nicholson,
B. Sicardy,
C. Sotin,
M.C. Chamberlain,
G. Hansen,
K. Hibbits, M. Showalter,
G. Filacchione
[show abstract]
[hide abstract]
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.
Icarus. 166(2003):75-84.
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A. Coradini,
F. Tosi,
A.I. Gavrishin,
F. Capaccioni,
P. Cerroni,
G. Filacchione,
A. Adriani,
R.H. Brown,
G. Bellucci,
V. Formisano, [......],
R.M. Nelson,
P.D. Nicholson,
B. Sicardy,
C. Sotin,
M.M. Hedman,
G.B. Hansen,
C.A. Hibbitts, M. Showalter,
C. Griffith,
G. Strazzulla
[show abstract]
[hide abstract]
ABSTRACT: We apply a multivariate statistical method to the Phoebe spectra collected by the VIMS experiment onboard the Cassini spacecraft during the flyby of June 2004. The G-mode clustering method, which permits identification of the most important features in a spectrum, is used on a small subset of data, characterized by medium and high spatial resolution, to perform a raw spectral classification of the surface of Phoebe. The combination of statistics and comparative analysis of the different areas using both the VIMS and ISS data is explored in order to highlight possible correlations with the surface geology. In general, the results by Clark et al. [Clark, R.N., Brown, R.H., Jaumann, R., Cruikshank, D.P., Nelson, R.M., Buratti, B.J., McCord, T.B., Lunine, J., Hoefen, T., Curchin, J.M., Hansen, G., Hibbitts, K., Matz, K.-D., Baines, K.H., Bellucci, G., Bibring, J.-P., Capaccioni, F., Cerroni, P., Coradini, A., Formisano, V., Langevin, Y., Matson, D.L., Mennella, V., Nicholson, P.D., Sicardy, B., Sotin, C., 2005. Nature 435, 66–69] are confirmed; but we also identify new signatures not reported before, such as the aliphatic CH stretch at 3.53 μm and the ∼4.4 μm feature possibly related to cyanide compounds. On the basis of the band strengths computed for several absorption features and for the homogeneous spectral types isolated by the G-mode, a strong correlation of CO2 and aromatic hydrocarbons with exposed water ice, where the uniform layer covering Phoebe has been removed, is established. On the other hand, an anti-correlation of cyanide compounds with CO2 is suggested at a medium resolution scale.
Icarus.
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R.H. Brown,
K.H. Baines,
G. Bellucci,
J.-P. Bibring,
B.J. Buratti,
F. Capaccioni,
P. Cerroni,
R.N. Clark,
A. Coradini,
D.P. Cruikshank, [......],
R.M. Nelson,
P.D. Nicholson,
B. Sicardy,
C. Sotin,
S. Amici,
M.A. Chamberlain,
G. Filacchione,
G. Hansen,
K. Hibbitts, M. Showalter
[show abstract]
[hide abstract]
ABSTRACT: The Cassini Visual and Infrared Mapping Spectrometer (VIMS) is an imaging spectrometer covering the wavelength range 0.3–5.2 μm in 352 spectral channels, with a nominal instantaneous field of view of 0.5 mrad. The Cassini flyby of Jupiter represented a unique opportunity to accomplish two important goals: scientific observations of the jovian system and functional tests of the VIMS instrument under conditions similar to those expected to obtain during Cassini's 4-year tour of the saturnian system. Results acquired over a complete range of visual to near-infrared wavelengths from 0.3 to 5.2 μm are presented. First detections include methane fluorescence on Jupiter, a surprisingly high opposition surge on Europa, the first visual-near-IR spectra of Himalia and Jupiter's optically-thin ring system, and the first near-infrared observations of the rings over an extensive range of phase angles (0–120°). Similarities in the center-to-limb profiles of H+3 and CH4 emissions indicate that the H+3 ionospheric density is solar-controlled outside of the auroral regions. The existence of jovian NH3 absorption at 0.93 μm is confirmed. Himalia has a slightly reddish spectrum, an apparent absorption near 3 μm, and a geometric albedo of 0.06±0.01 at 2.2 μm (assuming an 85-km radius). If the 3-μm feature in Himalia's spectrum is eventually confirmed, it would be suggestive of the presence of water in some form, either free, bound, or incorporated in layer-lattice silicates. Finally, a mean ring-particle radius of 10 μm is found to be consistent with Mie-scattering models fit to VIMS near-infrared observations acquired over 0–120° phase angle.
Icarus.
-
G. Filacchione,
F. Capaccioni,
F. Tosi,
A. Coradini,
P. Cerroni,
R. N. Clark,
P. D. Nicholson,
J.N. Cuzzi,
M.H. Hedman, M. Showalter,
R. Jaumann,
K. Stephan,
D. P. Cruikshank,
R.H. Brown,
K. H. Baines,
R.M. Nelson,
T. B. McCord
Saturn Book Symposium entitled "Saturn After Cassini-Huygens";
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V. Formisano,
E. D'Aversa,
G. Bellucci,
K.H. Baines,
J.P. Bibring,
R.H. Brown,
B.J. Buratti,
F. Capaccioni,
P. Cerroni,
R.N. Clark, [......],
V. Mennella,
R.M. Nelson,
P.D. Nicholson,
B. Sicardy,
C. Sotin,
M.C. Chamberlain,
G. Hansen,
K. Hibbits, M. Showalter,
G. Filacchione
[show abstract]
[hide abstract]
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.
Icarus.
-
G. Filacchione,
F. Capaccioni,
T.B. McCord,
A. Coradini,
P. Cerroni,
G. Bellucci,
F. Tosi,
E. D'Aversa,
V. Formisano,
R.H. Brown, [......],
D.L. Matson,
V. Mennella,
R.M. Nelson,
P.D. Nicholson,
B. Sicardy,
C. Sotin,
G. Hansen,
K. Hibbitts, M. Showalter,
S. Newman
[show abstract]
[hide abstract]
ABSTRACT: Saturn's icy satellites are among the main scientific objectives of the Cassini-VIMS (Visual and Infrared Mapping Spectrometer) experiment. This paper contains a first systematic and comparative analysis of the full-disk spectral properties of Dione, Enceladus, Epimetheus, Hyperion, Iapetus, Mimas, Phoebe, Rhea and Tethys as observed by VIMS from July 2004 to June 2005. The disk integrated properties (350–5100 nm reflectance spectra and phase curves at 550–2232 nm) and images of satellites are reported and discussed in detail together with the observed geometry. In general, the spectra in the visible spectral range are almost featureless and can be classified according to the spectral slopes: from the bluish Enceladus and Phoebe to the redder Iapetus, Hyperion and Epimetheus. In the 1000–1300 nm range the spectra of Enceladus, Tethys, Mimas and Rhea are characterized by a negative slope, consistent with a surface largely dominated by water ice, while the spectra of Iapetus, Hyperion and Phoebe show a considerable reddening pointing out the relevant role played by darkening materials present on the surface. In between these two classes are Dione and Epimetheus, which have a flat spectrum in this range. The main absorption bands identified in the infrared are the 1520, 2020, 3000 nm H2O/OH bands (for all satellites), although Iapetus dark terrains show mostly a deep 3000 nm band while the 1520 and 2020 nm bands are very faint. In this spectral range, the Iapetus spectrum is characterized by a strong reddening. The CO2 band at 4260 nm and the Fresnel ice peak around 3100 nm are evident only on Hyperion, Phoebe and Iapetus. The phase curves at 550 and at 2232 nm are reported for all the available observations in the 0°–144° range; Rhea shows an opposition surge at visible wavelengths in the 0.5°–1.17° interval. The improvement on the retrieval of the full-disk reflectance spectra can be appreciated by a direct comparison with ground-based telescopic data available from literature. Finally, data processing strategies and recent upgrades introduced in the VIMS-V calibration pipeline (flat-field and destriping–despiking algorithm) are discussed in appendices.
Icarus.
