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Spectrophotometry and organic matter on Iapetus. 1. Composition models
1Laboratory for Planetary Studies, Cornell University, Ithaca, New York, USA.
Journal of Geophysical Research
|April 25, 1995
Summary
The dark material on Saturn's moon Iapetus is likely a mixture of poly-hydrogen cyanide (poly-HCN), Murchison organic residue, and water ice. This composition best explains Iapetus's unique hemispheric albedo asymmetry.
Area of Science:
- Planetary Science
- Astrochemistry
- Surface Physics
Background:
- Iapetus exhibits extreme hemispheric albedo asymmetry, unique among solar system bodies.
- The leading hemisphere is significantly darker than the trailing hemisphere, prompting investigation into its composition.
Purpose of the Study:
- To identify the composition of the dark material on Iapetus's leading hemisphere.
- To model potential mixtures that explain the observed spectral and albedo properties.
Main Methods:
- Application of Hapke scattering theory to model light interaction with surface materials.
- Laboratory measurement of optical constants for candidate materials.
- Extensive computer grid search of three-component mixtures (intraparticle, particle, areal).
Main Results:
- An intraparticle mixture of 25% poly-HCN, 10% Murchison residue, and 65% water ice provided the best fit to Iapetus's dark material spectrum, albedo, and phase behavior.
- Alternative models involving kerogen, ice tholin, and Titan tholin also yielded good fits.
- Poly-hydrogen cyanide (poly-HCN) was identified as a crucial component in most successful models.
Conclusions:
- The dark material on Iapetus is likely an intraparticle mixture dominated by water ice, with significant contributions from poly-HCN and Murchison organic residue.
- Further high-resolution observations near 4.5 micrometers could confirm the presence of poly-HCN.