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Title: SILICATES ON IAPETUS FROM CASSINI’S COMPOSITE INFRARED SPECTROMETER

We present the first spectral features obtained from Cassini’s Composite Infrared Spectrometer (CIRS) for any icy moon. The spectral region covered by CIRS focal planes (FP) 3 and 4 is rich in emissivity features, but previous studies at these wavelengths have been limited by low signal-to-noise ratios (S/Ns) for individual spectra. Our approach is to average CIRS FP3 spectra to increase the S/N and use emissivity spectra to constrain the composition of the dark material on Iapetus. We find an emissivity feature at ∼855 cm{sup −1} and a possible doublet at 660 and 690 cm{sup −1} that do not correspond to any known instrument artifacts. We attribute the 855 cm{sup −1} feature to fine-grained silicates, similar to those found in dust on Mars and in meteorites, which are nearly featureless at shorter wavelengths. Silicates on the dark terrains of Saturn’s icy moons have been suspected for decades, but there have been no definitive detections until now. Serpentines reported in the literature at ambient temperature and pressure have features near 855 and 660 cm{sup −1}. However, peaks can shift depending on temperature and pressure, so measurements at Iapetus-like conditions are necessary for more positive feature identifications. As a first investigation, wemore » measured muscovite at 125 K in a vacuum and found that this spectrum does match the emissivity feature near 855 cm{sup −1} and the location of the doublet. Further measurements are needed to robustly identify a specific silicate, which would provide clues regarding the origin and implications of the dark material.« less
Authors:
;  [1] ;  [2] ;  [3] ;  [4] ; ;  [5] ;  [6]
  1. School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA (United States)
  2. Planetary Science Institute, Tucson, AZ (United States)
  3. Southwest Research Institute, Boulder, CO (United States)
  4. NASA Goddard Space Flight Center, Greenbelt, MD (United States)
  5. Jet Propulsion Laboratory, Pasadena, CA (United States)
  6. Caltech, Pasadena, CA (United States)
Publication Date:
OSTI Identifier:
22518874
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 811; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; AMBIENT TEMPERATURE; EMISSIVITY; INFRARED SPECTRA; MARS PLANET; METEORITES; MOON; MUSCOVITE; PRESSURE DEPENDENCE; SATURN PLANET; SIGNAL-TO-NOISE RATIO; SILICATES; SURFACES; TEMPERATURE DEPENDENCE