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Galileo to Jupiter (included NASA Ames partnership)
Launched in 1989 aboard space shuttle Atlantis, Galileo explored Jupiter and its moons. Upon arrival at Jupiter in December 1995, the Galileo spacecraft delivered a probe that descended into the giant planet's atmosphere. The orbiter completed many flybys of Jupiter's major moons, reaping a variety of science discoveries. The mission ended on Sept. 21, 2003, when the spacecraft plunged into Jupiter's atmosphere.


Galileo was launched Oct. 18, 1989, from Kennedy Space Center, Florida, carried into Earth orbit in the cargo bay of space shuttle Atlantis. A two-stage solid-fuel motor called an inertial upper stage then propelled Galileo onto its interplanetary flight path. Although earlier plans called for Galileo to use a more powerful upper stage so that it could fly directly to Jupiter, the final flight took the spacecraft by other planets first so that it could gain energy from the gravity of each. Galileo flew past Venus on Feb. 10, 1990, and then twice past Earth -- once on Dec. 8, 1990, and again on Dec. 8, 1992.

Also en route to Jupiter, Galileo flew close to two asteroids, the first such visits by any spacecraft. It encountered the asteroid Gaspra on Oct. 29, 1991, and the asteroid Ida on Aug. 28, 1993. During the latter part of its interplanetary cruise, Galileo was used to observe the collisions of fragments of Comet Shoemaker-Levy with Jupiter in July 1994.

Galileo arrived at Jupiter on Dec. 7, 1995, entering orbit and dropping its instrumented probe into the giant planet's atmosphere. The Galileo atmospheric probe was managed by NASA Ames Research Center, Moffett Field, Calif. Measurements of temperature, pressure and vertical winds revealed several discoveries as the Galileo Probe plunged into Jupiter's atmosphere. The Atmosphere Structure Instrument (ASI) measured temperature, pressure and density.

The probe also included a mass spectrometer that measured the chemical composition of Jupiter's atmosphere.

"Measuring the composition of Jupiter's atmosphere was a primary scientific objective of the probe, because we knew it could change our understanding of Jupiter's formation and evolution," said Galileo probe project scientist Dr. Richard Young of NASA Ames Research Center, Moffett Field, Calif. "These latest probe results have done exactly that, and the measurements are the sort that could only have been obtained by in-situ measurements from an entry probe."

The spectrometer detected in Jupiter's atmosphere higher than expected concentrations of argon, krypton and xenon, three chemical elements called noble gases because they are very independent and do not combine with other chemicals. Tiny traces of these gases are found in Earth's atmosphere, and argon is sometimes used like neon in advertising signs.

When it dropped 156 kilometers (97 miles) through Jupiter's atmosphere, the Galileo probe relayed data back to the main Galileo spacecraft more than 209,215 kilometers (130,000 miles) overhead for storage and transmission to Earth. The probe descended deeper into the atmosphere than expected, but was finally overcome by Jupiter's high temperatures and pressures.

The Galileo spacecraft, meanwhile, orbited Jupiter and its moons for nearly four years, beaming back to Earth thousands of pictures and a wealth of scientific data. Its two-year, primary mission ended in December 1997, but the mission was continued with an initial two-year extension.

Galileo discovered strong evidence that Jupiter's moon Europa has a melted saltwater ocean under an ice layer on its surface. The spacecraft also found indications that two other moons, Ganymede and Callisto, have layers of liquid saltwater as well. Other major science results from the mission include details of varied and extensive volcanic processes on the moon Io, measurements of conditions within Jupiter's atmosphere, and discovery of a magnetic field generated by Ganymede.

The mission finally ended on Sept. 21, 2003, when the spacecraft plunged into Jupiter's atmosphere. This planned maneuver prevented the risk of Galileo drifting to an unwanted impact with the moon Europa, which may harbor a subsurface ocean.

Key Mission People
Galileo probe project scientist Dr. Richard Young of NASA Ames Research Center, Moffett Field, Calif.

Related links:

Galileo Probe Results Suggest Jupiter had an Ancient, Chilly Past

Solar System Exploration - Galileo Legacy Site

Past Missions - Galileo

Galileo - Journey to Jupiter

Online from Jupter Update