36th DPS Meeting, 8-12 November 2004
Session 24 Icy Satellites
Oral, Wednesday, November 10, 2004, 1:30-3:00pm, Lewis

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[24.05] Carbon dioxide in the Surfaces of the Icy Satellites

C. A. Hibbitts (Planet. Sci. Inst.), J. Szanyi (Pacific NW Nat. Lab), T.B. McCord (Planet. Sci. Inst.)

Carbon dioxide has been detected on the surfaces of the Galilean satellites [Carlson et al., 1996; McCord et al., 1998], the Uranian satellite Ariel [Grundy, 2003], the Saturnian satellite Phoebe [NASA Press Release, 2004], and is ubiquitous in comets and the interstellar medium (ISM) [e.g. Vidali et al., 2004]. The physical state and distribution of CO2 on these objects can help us understand its origin and may help us understand the objects' geological histories. For instance, a small amount of CO2 exists in the fine-grained (and thus `recent') ice on the leading hemisphere of Europa. Carlson, [2004] infers an exogenic origin: radiolysis of carbonaceous material. Hibbitts et al., [2000; 2002] infer from spectral characteristics and surface distributions that the CO2 on Ganymede and Callisto is previously outgassed endogenic CO2 now trapped in non-ice material(s). They further argue that distributions of CO2 on Ganymede and Callisto suggest Ganymede's interior is depleted in CO2 relative to Callisto, consistent with its more extensive tectonic past [e.g. Pappalardo et al., 1998]. The CO2 so far identified on all Jovian and Saturnian satellites seems to be molecules bound/trapped to a host material, mostly nonice. IR spectra of the ISM also suggests some CO2 is bound material. Thus, bound CO2 seems to be spectrally, and potentially compositionally, significant on objects' surfaces in the outer solar system and beyond. To explore the physical state and associated mechanisms of CO2 bound to non-ice materials we conducted CO2 adsorption experiments with several candidate outer solar system non-ice materials at relevant temperatures and pressures. We have found that CO2 adsorbs to certain clays and zeolites but not to at least some oxides and oxyhydroxides. The spectral characteristics of adsorbed CO2 are dependent on the exact composition (which cation is present) and there may be temperature dependences.

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