Distributions of CO₂ and SO₂ on the surface of Callisto

Abstract

Abstract. Absorption bands in the infrared reflectance spectra from the Galileo Near-Infrared Mapping Spectrometer (NIMS) which are attributed to the presence of CO 2 and SO 2 on the surface of Callisto have been analyzed and mapped in detail. CO 2 of varying concentrations appears to exist everywhere on Callisto, except at higher latitudes, where it may be masked by frost. The CO 2 concentration on the trailing hemisphere has a longitudinal distribution largely consistent with a sinusoid centered on the equator near 270 ø longitude. The approximately sinusoidal pattern suggests that exogenic effects related to Jupiter's corotating magnetic field are involved. Closer inspection of both hemispheres reveals that in many cases, visibly bright and ice-rich impact craters have high CO 2 concentrations within or near them. The CO 2 sometimes appears to be associated more with dark material near the craters than with the water ice. These correlations suggest impact processes may also affect the distribution of CO 2 on the surface of Callisto. The center of the absorption band has been refined to be at 4.258 +_ 0.004 pm. The presence of a single band shape and band minimum wavelength position in all data sets for the CO 2 absorption implies the physical state of CO 2 is similar over the surface of Callisto. The distribution of SO 2 on the surface is less well defined owing to characteristically shallower band depths, but it appears generally mottled, with some areas of high concentrations correlated with ice-rich impact craters. Large-scale patterns include the depletion of SO 2 in the polar regions and a depletion of SO 2 on the trailing side relative to the leading side. There is no sinusoidal pattern to this depletion. The center of the SO 2 band is determined to be between 4.01 and 4.02 pm.

Callisto: New Insights fromGalileoDisk‐resolved UV Measurements

“…Candidates for the non-water ice components include phyllosilicates (Roush et al 1990;Calvin & Clark 1991), and small features due to organics were suggested to be present at NIR wavelengths (McCord et al 1997). Carbon dioxide is present at the surface, particularly in dark regions, possibly adsorbed or trapped in grains of non-ice material, based on the presence of an absorption feature at 4.25 m (Hibbitts et al 2000), and this surface CO 2 feature is distinct from the absorption expected from crystalline CO 2 .…”

Laboratory spectra of CO2 vibrational modes in planetary ice analogs

“…Observed temperatures of some jovian and saturnian satellites and positions of the CO 2 stretch mode in IR absorption spectra compared with positions and temperatures of CO 2 stretch mode profiles in laboratory data from this study. Asymmetric stretch mode band positions are from the following: the saturnian satellite surfaces are from Cruikshank et al (2010), the surface of Ganymede is from Hibbitts et al (2003), and the surface of Callisto is from Hibbitts et al (2000). Surface temperatures of Dione, Iapetus, and the jovian satellites are from Grundy et al (1999), of Phoebe is from Ostro et al (2006), and of Hyperion is from Cruikshank et al (2007).…”

“…11. Observations were taken from published data from ground-based telescopes, NIMS aboard the Galileo spacecraft, and VIMS aboard the Cassini probe (Grundy et al, 1999;Hibbitts et al, 2000Hibbitts et al, , 2003Ostro et al, 2006;Cruikshank et al, 2007Cruikshank et al, , 2010. Temperatures for the surfaces of the jovian satellites, Dione, and Iapetus were derived from an average disk temperature and the IR absorption features of H 2 O-ice from the surfaces (Grundy et al, 1999).…”

“…As in ISM ices, additional compounds are often present in these H 2 O-dominated ices (e.g., Grundy et al, 1999;Cruikshank et al, 2010). For example, spectroscopic data from the Near-infrared mapping spectrometer (NIMS) aboard the Galileo spacecraft that explored satellites such as Ganymede and Callisto indicated the presence of CO 2 within the host ice (Carlson et al, 1996;McCord et al, 1998;Hibbitts et al, 2000Hibbitts et al, , 2002Hibbitts et al, , 2003Cruikshank et al, 2010). Temperatures of H 2 O-dominated ice mixtures typically found on outer Solar System surfaces typically range from 50 to 160 K. These temperatures can vary with time and location, depending on sunlight exposure, local geological activity, etc.…”

Geology and Composition of the Icy Galilean Satellites

“…Absorption near 4.25 /im is interpreted as CO2, and its spectral character suggests that it is trapped within or bound to dark surface materials. The CO2 absorption shows correlation to the trailing side of the satellite, suggesting a link to bombardment by corotating plasma; moreover, it is correlated with some bright impact craters (Hibbitts, McCord, & Hansen 2000a). CO2 is a possible component of Callisto's icy subsurface, and its sublimation may contribute to generation of the satellite's dark 620 Pappalardo surface materials as a refractory lag (Moore et al 1999).…”