Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.0307p&link_type=abstract
American Astronomical Society, DPS meeting #41, #3.07
Astronomy and Astrophysics
Astronomy
Scientific paper
Carbon dioxide has been detected on Iapetus (Buratti et al., 2005) and is correlated with the dark material, mostly at mid-latitudes on the leading face of Iapetus (Palmer and Brown, in preparation). The average absorption feature of CO2 in the dark region is 24.7%; if it were a thin veneer of CO2 ice, it would be 14 um thick. Estimating the surface area of dark material and extrapolating gives a total CO2 budget of 8 x 107 kg on the surface of Iapetus.
Volatile studies indicate that the surface of Iapetus is too hot to have CO2 ice remain on the surface for more than a few hundred years (Palmer and Brown, 2008). It has been suggested that complexing of volatiles, such as in clathrates, fluid or gas inclusions, or adsorption, would increase the stability on the Jovian and Saturnian satellites, increasing their residence times (McCord; et al., 1998; Hibbitts et al., 2001, 2002, 2007).
While complexing would increase carbon dioxide's thermal stability, the resident time of CO2 on Iapetus would remain short due to the effect of UV radiation. We calculated the photodissociation rate for CO2 and found that the entire budget of CO2 on Iapetus would be destroyed in less than one Earth year.
If we assume a steady-state system on Iapetus (photodissociation equal to photo-generation) approx. 108 kg will be destroyed and produced every Earth year. Unless the complexing mechanism provides some shielding from UV radiation while still allowing the detection of the 4.26-micron CO2 band, then a source of CO2 is required. We suggest that the source of CO2 is photolytic production from water ice and carbonaceous material.
Brown Harvey R.
Palmer Eric Edward
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