In the end, the Galileo spacecraft tasted Jupiter before taking a final plunge into the planet's crushing atmosphere. The mission team gathered at NASA’s Jet Propulsion Laboratory to watch the final few hours of science data in real time leading up to impact. The mission ended Sunday, Sept. 21, 2003.
"It has been a fabulous mission for planetary science, and it is hard to see it come to an end," Dr. Claudia Alexander, Galileo project manager at NASA's Jet Propulsion Laboratory, said in 2003.
The spacecraft was purposely put on a collision course with Jupiter to eliminate any chance of an unwanted impact between the spacecraft and Jupiter’s moon Europa, which Galileo discovered is likely to have a subsurface ocean. The long-planned impact is necessary now that the onboard propellant is nearly depleted.
Without propellant, the spacecraft would not be able to point its antenna toward Earth nor adjust its trajectory, so controlling the spacecraft would no longer be possible.
Launched in the cargo bay of Space Shuttle Atlantis in 1989, the mission has produced a string of discoveries while circling the solar system's largest planet, Jupiter, 34 times.
Galileo was the first mission to measure Jupiter's atmosphere directly with a descent probe and the first to conduct long-term observations of the jovian system from orbit. It found evidence of subsurface liquid layers of saltwater on Europa, Ganymede and Callisto and it examined a diversity of volcanic activity on Io. Galileo is the first spacecraft to fly by an asteroid and the first to discover a moon of an asteroid.
The prime mission ended six years ago, after two years of orbiting Jupiter. NASA extended the mission three times to continue taking advantage of Galileo's unique capabilities for accomplishing valuable science. The mission was possible because it drew its power from two long-lasting radioisotope thermoelectric generators provided by the Department of Energy.
From launch to impact, the spacecraft has traveled about 2.8 billion miles (4,631,778,000 kilometers).
Its entry point into the giant planet’s atmosphere was about 1/4 degree south of Jupiter's equator. If there were observers floating along at the cloud tops, they would have seen Galileo streaming in from a point about 22 degrees above the local horizon.
Streaming in could also be described as screaming in, as the speed of the craft relative to those observers was about 48.2 kilometers per second (nearly 108,000 miles per hour). That is the equivalent of traveling from Los Angeles to New York City in 82 seconds. In comparison, the Galileo atmospheric probe, aerodynamically designed to slow down when entering, and parachute gently through the clouds, first reached the atmosphere at a slightly more modest 47.6 kilometers per second (106,500 miles per hour).
Several missions have since been slated to follow up on Galileo’s legacy. NASA’s Juno spacecraft arrived at Jupiter in 2015 to study the giant planet’s interior. NASA is currently developing Europa Clipper, an orbiter that will pursue new details about the habitability of the global saltwater ocean Galileo discovered beneath the icy crust of Europa. The European Space Agency also is developing a new Jupiter mission called JUICE.