Physics
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.p11b0107p&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #P11B-0107
Physics
6020 Ices, 6280 Saturnian Satellites
Scientific paper
Cassini VIMS detected CO2 on the surface of Iapetus during the New Year 2005 flyby (Buratti et al., 2005). We are analyzing the effects of sublimation and transport if the CO2 is present as ice. Previous work (Lebofsky, 1975)
analyzed the stability of CO2 in the solar system and showed that CO2 would be quickly lost from a body at Saturn distances. However, large body effects such as gravity or particle accumulation into cold traps at the body's poles were not considered as Lebofsky's analysis focused on comets.
The amount of CO2 that will sublimate is determined by the surface temperature. Our model calculates temperature using thermal conduction, black body radiation and the
cooling effect due to latent heat. We use an extremely small thermal inertia of 30 watts m-2 K-1 sec-1/2 suggested by Cassini CIRS (Spencer et al., 2005). We use an albedo of 0.04 for the dark side and 0.5 for the bright side.
The sublimation rate outside of the polar region is between 2.5 and 7 cm/year. Once it sublimates we assume CO2 leaves the surface with no preference in azimuth or elevation and has an initial velocity described by a Maxwell-Boltzmann
distribution.
Material with less than escape velocity (591 m/s) will move around the surface until caught in Iapetus's polar region. Once inside the polar region, the CO2 will stay for extended period of time, up to thousands of years. The small portion of CO2 that reaches escape velocity will be lost to the system. The hotter temperatures near the equator cause not only more CO2 to sublimate, but also a higher fraction to reach escape velocity. The rate
of loss can be as high as 0.25 cm/year. However, once the ice moves near the poles, the rate of material lost drops several orders of magnitude.
We will be reporting the results of computer simulation of the transport of CO2 on Iapetus.
References: Buratti, B. J. et al. (2005). Cassini VIMS Observations of Iapetus: Detection of CO2, ApJ, 622 p.p. L149-L152. Lebofsky, L. A (1975). Stability of Frosts in the Solar System. Icarus, 25. Spencer, J. R., Pearl, J. C., and Segura, M. (2005). Cassini CIRS observations of Iapetus' thermal emission. LPSC XXVI, 2305.
Brown Harvey R.
Palmer Eric Edward
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