... This dramatic high resolution picture looking across the edge of the Sun was taken April 24th by a telescope on board the newly launched Transition Region and Coronal Explorer (TRACE) satellite. ... Callisto Enhanced . ... Callisto is half rock and half ice. This moon of Jupiter is approximately the size of the planet Mercury, making it the third largest moon in the Solar System, after Ganymede and Titan. Callisto.. ... Skylab Over Earth . ... Did a gamma-ray burst precede this supernova? ...