... This mystery came to light after the robot spacecraft Galileo, in orbit around Jupiter since 1995, swooped past the dark moon in May. ... Uranus is composed mostly of rock and ices, but with a thick hydrogen and helium atmosphere. ... Pioneer 10: The First 7 Billion Miles . ... Shown in this stunning false-color Hubble Space Telescope image, the galaxy's disk - composed of spectacular star clusters in winding spiral arms and dramatic dark lanes of dust - spans some 70,000 light-years. ...