Callisto from JWST: CO 2 -rich Terrain on the Leading Hemisphere and Global Patterns of H 2 O Ice

We present maps of H 2 O, CO 2 , and a 4.57 µ m spectral feature across Callisto’s surface observed using the James Webb Space Telescope (JWST). H 2 O ice was mapped by measuring band parameters of the 3.1 µ m Fresnel peak across the leading and trailing hemispheres under a simplified assumption of crystalline ice. We update the CO 2 solid-phase, CO 2 gas, and 4.57 µ m feature band depth maps originally presented in R. J. Cartwright et al. with a new JWST observation of Callisto centered on Valhalla, the largest multi-ring impact basin in the solar system. Our H 2 O ice map shows that the Fresnel peak on the trailing hemisphere exhibits a bullseye pattern that is weaker at low latitudes, and on the leading hemisphere its strength is associated with impacts. This dichotomy is possibly related to the Jovian magnetospheric plasma impinging on the trailing hemisphere. Our solid-phase CO 2 map reveals an enhancement in the vicinity of the Lofn/Heimdall impact craters, a region that may be the largest reservoir of nonradiolytic CO 2 on Callisto’s surface. The gas-phase CO 2 exhibits a patchy spatial distribution and does not clearly correlate with solid CO 2 .