This is a Hubble Space Telescope "family portrait"

DECEMBER 4: This is a Hubble Space Telescope "family portrait" of the four largest moons of Jupiter, released 10 October, first observed by the Italian scientist Galileo Galilei nearly four centuries ago. Located approximately one-half billion miles away, the moons are so small that, in visible light, they appear as fuzzy disks in the largest ground-based telescopes. Over the past year Hubble has charted new volcanic activity on Io's active surface, a faint oxygen atmosphere on the moon Europa, identified ozone on the surface of Ganymede and shown fresh ice on the surface of Callisto that may indicate impacts from micrometeorites and charged particles from Jupiter's magnetosphere. The Galileo probe is due to land on Jupiter 07 December. NASA/AFP PHOTO (Photo credit should read NOL/AFP via Getty Images)