a large white ball with two smaller planets in the background

HST/WFPC2 Image of Jupiter and Ganymede Taken April 9, 2007 Caption NASA's Hubble Space Telescope has caught Jupiter's moon Ganymede playing a game of "peek-a-boo." In this crisp Hubble image, Ganymede is shown just before it ducks behind the giant planet. Credits NASA, ESA, and E. Karkoschka (University of Arizona)