By studying Jupiter we learn about how our solar system formed and evolved, and how countless others in the galaxy and beyond do as well. Jupiter's four planet-like moons have features like volcanoes and subsurface oceans, making Jupiter a miniature Solar System of its own.
Jupiter is not only an interesting scientific destination but also an important waypoint for spacecraft heading further into the Solar System. The gas giant's immense gravity field can provide a boost and trajectory change for spacecraft heading to even further destinations.
Launch: October 18, 1989
Jupiter probe descent: December 7, 1995
Jupiter orbit insertion: December 8, 1995
Plunge into Jupiter: September 22, 2003
NASA's Galileo was the first spacecraft to orbit Jupiter. It revealed the structure of the planet's magnetic filed and intense radiation belts, made the first detailed maps of Jupiter's major moons, hinted at a possible underground ocean on Europa, sent the first probe to sample a gas planet's atmosphere, and more.