On Sept. 21, 2003, NASA's Galileo mission to Jupiter and its moons came to an end.
After 14 years of exploration, the Galileo spacecraft intentionally fell into Jupiter and disintegrated in the planet's dense atmosphere. Galileo launched in 1989 from the payload bay of the space shuttle Atlantis and arrived at Jupiter in 1995.
It was the first spacecraft to orbit Jupiter and the first to send a probe into its atmosphere. It discovered evidence of saltwater below the surfaces of three of Jupiter's moons — Europa, Ganymede and Callisto. It was purposely put on a collision course with Jupiter because it was running out of fuel, and NASA wanted to make sure that it wouldn't impact any of Jupiter's moons that could harbor life in their subsurface oceans.
Why it mattered
NASA's Galileo mission to Jupiter was a first-of-its-kind mission, a dedicated orbiter designed to survive the extreme harsh radiation environment around the largest planet in our solar system in an attempt to uncover its secrets.
Named in honor of Galileo Galilei, the Italian Renaissance scientist who discovered Jupiter's major moons in 1610, the Galileo spacecraft carried nine primary instruments to study the giant planet. It also carried a small "Atmospheric Probe," a module just 50 inches (127 centimeters) wide that weighed 750 pounds (339 kilograms) and carried its own instrument suite to measure Jupiter's atmosphere as the probe plunged into the planet.
Galileo made a host of Jupiter discoveries during its storied 14-year mission (which NASA extended three times before the end). The probe discovered that Ganymede, the largest moon in the solar system, has its own magnetic field. It revealed that Jupiter's volcanic moon Io has 100 times more volcanic activity that the Earth, made the first observations of ammonia clouds on Jupiter. And then there is Jupiter's moon Europa, where Galileo found evidence of a subsurface ocean buried beneath an icy crust. That's just a tiny bit of the many Jupiter revelations made by Galileo's science team.
Galileo completed its primary mission in December 1997, with its mission extensions stretching its flight through 2003. In all, Galileo made 35 flybys of Jupiter's moons including 11 of Europa, eight each of Callisto and Ganymede, seven of Io and one of Amalthea.
The Galileo spacecraft set the stage for dedicated orbiters to the outer planets, including NASA's Cassini spacecraft to Saturn and the Juno spacecraft at Jupiter today. Galileo's demise also demonstrated a bit of planetary protection for NASA, which would later recreate the death dive at Saturn with Cassini's Grand Finale as way to protect that planet's icy moons from contamination as well.
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