Galileo

Galileo launched from the Space Shuttle Atlantis in October 1989 and took a six-year gravity-assist route to become the first spacecraft to orbit Jupiter. Along the way it made the first asteroid flybys and discovered the first asteroid moon; on arrival in 1995 it dropped a probe into Jupiter’s atmosphere, which survived 58 minutes of crushing descent while relaying the first direct measurements from inside a gas giant.

Over eight years and 34 orbits, Galileo transformed Jupiter’s moons from points of light into worlds — most profoundly Europa, where magnetic and gravity data revealed a global saltwater ocean beneath the ice, now a prime target in the search for life. To protect that ocean from contamination, Galileo was deliberately flown into Jupiter in 2003.