Intrigued by the Voyager findings at Jupiter, planetary scientists once again turned their attention toward that planet in the early 1980s. They designed a mission to orbit Jupiter and monitor the planet and its satellites for at least two years. In addition, a probe was to be deployed from the spacecraft into Jupiter's atmosphere.
The launch was scheduled for May 1986 from a space shuttle, but the Challenger disaster in January of that year put all shuttle missions on indefinite hold. By the time shuttles were flying again, nearly two years later, the launch window that had afforded a direct path to Jupiter had come and gone.
Galileo did not have enough power for a direct flight, so a three-year flight path was designed to "sling" Galileo to Jupiter using gravity assists from Venus and Earth. The flight path also brought it near asteroids Gaspra in 1991 and Ida in 1993. High-resolution images of Gaspra indicated that it was possibly a fragment of a larger body, while those of Ida revealed that it was orbited by a small moon.
The spacecraft finally made it to Jupiter in December 1995. On 7 December 1995, the probe parachuted into the upper cloud decks and returned 57 minutes of data before the signal was lost. Scientists were surprised to discover that, rather than being rich in water, oxygen, carbon, and other materials, Jupiter's mostly hydrogen atmosphere was rather primitive and unprocessed, resembling that of the Sun. Moreover, its atmosphere was dry, even clear in places, with no trace of water vapor or ice. The atmosphere was also denser and windier than expected. It is possible that the probe entered an area that was much drier than the rest of the atmosphere, so its findings are not conclusive.
Meanwhile, the orbiter has returned tantalizing data on the Galilean satellites (so called because they were first seen from Earth by Galileo), discovering, among other things, that Europa may have a relatively thin icy crust covering a mantle of liquid water or slush. This concoction may contain chemicals that could nurture life.