37th DPS Meeting, 4-9 September 2005
Session 58 Galilean Satellites

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[58.05] Radiolytic Production of Carbonic Acid and Applications to Jupiter's Icy Satellites

R. W. Carlson (Jet Propulsion Laboratory, California Institute of Technology), K. P. Hand (Stanford University), P. A. Gerakines (University of Alabama), M. H. Moore (Goddard Space Flight Center), R. L. Hudson (Eckerd College)

Europa, Ganymede, and Callisto all exhibit surficial CO2 and these satellites are heavily bombarded by energetic magnetospheric particles and solar ultraviolet radiation. Irradiation of CO2 in water ice produces carbonic acid, H2CO3 and it has been suggested that the 3.8-micron features in NIMS spectra of Ganymede and Callisto arise from H2CO3 (Hage et al., Science 279, 1332-1335, 1998). We combine results from proton- and ultraviolet-irradiated H2O:CO2 ices with recent electron irradiation results to investigate this possibility.

Carbonic acid production efficiencies, per 100 eV and at the same experimental conditions (H2O:CO2 = 1:1, 20 K), are G = 0.028 ± 0.024 and 0.030 ± 0.016 for proton and ultraviolet irradiation, respectively, whereas our provisional value for 10-keV electron irradiation is G = 0.011. Additionally, we provided sufficient electron dose to form equilibrium concentrations, where the rate of H2CO3 destruction equals the formation rate. The effective destruction cross section is about 4 x 10-17 cm2 and the equilibrium molar concentration ratio is [H2CO3]/[CO2] = 0.01. At equilibrium, the ratio of the equivalent widths of the H2CO3 3.8-micron and CO2 4.3-micron bands is about 0.07 and consistent with the observed ratio of 0.11 in Callisto spectra. The band positions of this feature in laboratory and Callisto spectra, 3.86 and 3.87 microns, respectively, are also in good agreement. Carbonic acid is a plausible candidate on the surfaces of Jupiter's icy satellites.

This work was supported by NASA's Planetary Geology and Geophysics and Exobiology Programs.

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Bulletin of the American Astronomical Society, 37 #3
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