This artist's rendering shows Galileo arriving at Jupiter on Dec. 7, 1995. Io is seen as a crescent moon to the left. Sent into space on Oct. 18, 1989, by the Space Shuttle Atlantis, Galileo launched the first probe into Jupiter's atmosphere. It then orbited the planet, taking observations until 2003, when NASA sent it plunging into the Jovian atmosphere. This was to avoid any chance contamination of Jupiter's moons with bacteria from Earth.