TY - JOUR
T1 - The surface composition of Iapetus
T2 - Mapping results from Cassini VIMS
AU - Clark, Roger N.
AU - Cruikshank, Dale P.
AU - Jaumann, Ralf
AU - Brown, Robert H.
AU - Stephan, Katrin
AU - Dalle Ore, Cristina Morea
AU - Eric Livo, K.
AU - Pearson, Neil
AU - Curchin, John M.
AU - Hoefen, Todd M.
AU - Buratti, Bonnie J.
AU - Filacchione, Gianrico
AU - Baines, Kevin H.
AU - Nicholson, Philip D.
N1 - Funding Information:
Work for this paper was funded by the NASA Cassini project. Some laboratory spectra for this study were obtained with NASA Cassini Data Analysis Program funding, R. Clark, PI.
PY - 2012/4
Y1 - 2012/4
N2 - Cassini VIMS has obtained spatially resolved imaging spectroscopy data on numerous satellites of Saturn. A very close fly-by of Iapetus on September 10, 2007 provided the best data on the spectral signature and spatial extent of dark material on Iapetus. This Cassini Rev 49 Iapetus fly-by provided spatially resolved imaging spectroscopy data of the dark material and the leading/trailing side transition from the dark material to visually bright ice on the trailing side. Compositional mapping and radiative transfer modeling shows that the dark material is composed of metallic iron, nano-size iron oxide (hematite), CO 2, H 2O ice, and possible signatures of ammonia, bound water, H 2 or OH-bearing minerals, trace organics, and as yet unidentified materials. CO 2 indicates a pattern of increasing CO 2 strength from the leading side apex to the transition zone to the icy trailing side. A Rayleigh scattering peak in the visible part of the spectrum indicates the dark material has a large component of fine, sub-0.5-μm diameter particles consistent with nanophase hematite and nanophase iron. Spectral signatures of ice also indicate that sub-0.5-μm diameter particles are present in the icy regions. Multiple lines of evidence point to an external origin for the dark material on Iapetus, including the global spatial pattern of dark material, local patterns including crater and cliff walls shielding implantation on slopes facing away from the leading side, exposing clean ice, and slopes facing the leading direction which show higher abundances of dark material. Multiple spectral features and overall spectral shape of the dark material on Iapetus match those seen on Phoebe, Hyperion, Dione, Epimetheus, Saturn's rings Cassini Division, and the F-ring implying the material has a common composition throughout the Saturn system. The dark material appears to have significant components of nanophase metallic iron and nanophase hematite contributing to the observed UV absorption. The blue scattering peak with a strong UV-visible absorption is observed in spectra of all satellites that contain dark material, again pointing to a common origin of contamination by metallic iron that is partially oxidized.
AB - Cassini VIMS has obtained spatially resolved imaging spectroscopy data on numerous satellites of Saturn. A very close fly-by of Iapetus on September 10, 2007 provided the best data on the spectral signature and spatial extent of dark material on Iapetus. This Cassini Rev 49 Iapetus fly-by provided spatially resolved imaging spectroscopy data of the dark material and the leading/trailing side transition from the dark material to visually bright ice on the trailing side. Compositional mapping and radiative transfer modeling shows that the dark material is composed of metallic iron, nano-size iron oxide (hematite), CO 2, H 2O ice, and possible signatures of ammonia, bound water, H 2 or OH-bearing minerals, trace organics, and as yet unidentified materials. CO 2 indicates a pattern of increasing CO 2 strength from the leading side apex to the transition zone to the icy trailing side. A Rayleigh scattering peak in the visible part of the spectrum indicates the dark material has a large component of fine, sub-0.5-μm diameter particles consistent with nanophase hematite and nanophase iron. Spectral signatures of ice also indicate that sub-0.5-μm diameter particles are present in the icy regions. Multiple lines of evidence point to an external origin for the dark material on Iapetus, including the global spatial pattern of dark material, local patterns including crater and cliff walls shielding implantation on slopes facing away from the leading side, exposing clean ice, and slopes facing the leading direction which show higher abundances of dark material. Multiple spectral features and overall spectral shape of the dark material on Iapetus match those seen on Phoebe, Hyperion, Dione, Epimetheus, Saturn's rings Cassini Division, and the F-ring implying the material has a common composition throughout the Saturn system. The dark material appears to have significant components of nanophase metallic iron and nanophase hematite contributing to the observed UV absorption. The blue scattering peak with a strong UV-visible absorption is observed in spectra of all satellites that contain dark material, again pointing to a common origin of contamination by metallic iron that is partially oxidized.
KW - Iapetus
KW - Ices, IR spectroscopy
KW - Satellites, composition
KW - Saturn, satellites
KW - Spectroscopy
UR - http://www.scopus.com/inward/record.url?scp=84862782798&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84862782798&partnerID=8YFLogxK
U2 - 10.1016/j.icarus.2012.01.008
DO - 10.1016/j.icarus.2012.01.008
M3 - Article
AN - SCOPUS:84862782798
SN - 0019-1035
VL - 218
SP - 831
EP - 860
JO - Icarus
JF - Icarus
IS - 2
ER -