Opposite the Valhalla impact on Callisto

Opposite the Valhalla impact on Callisto

Fig. 9.24 . This close-up image was purposely taken on the opposite point, or antipode, of Callisto’s huge Valhalla impact basin, created when an exceptionally large meteorite must have sent shocks into the moon’s interior and waves rippling across the surface. The internal shocks ought to focus at the antipode, as they did for the Callisto impact on Mercury, creating a grooved and hilly terrain. The absence of such terrain at the Valhalla antipode suggests that Callisto has liquid water in its interior, which dispersed the seismic shocks. Magnetic field measurements also suggest that Callisto has a layer of liquid water deep below its surface. This image was taken from the Galileo spacecraft on 25 May 2001. (Courtesy of NASA/JPL/U. Arizona.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University