In mid-October of 1989 the Space Shuttle Atlantis (STS-34) took off to deliver into space a unique craft set to explore Jupiter and its moons. The Galileo orbiter had a long mission ahead of it — six years — and spent a further eight in orbit, launching the first ever probe into the gas giant’s atmosphere, studying its magnetic field, its rings and its moons. Jupiter was known to be a rather inhospitable place, but its moons — Europa in particular — were found to possibly contain liquid water under the icy surface. That discovery prompted NASA to send the Galileo on a suicide mission into Jupiter.

On this day, September 21, in 2003, the Galileo mission came to a plunging end, as the orbiter used up what little fuel it had left to dip lower into Jupiter, from where the planets’ gravity will pull it relentlessly and powerfully to the surface.

While the Galileo could have remained in orbit for a great deal longer, it was running out of fuel, and would have no way to maneuver if a slight shift in Jupiter’s magnetic field would send the craft careening through the Jovian system out of control. The fear for NASA would be that Galileo might crash and contaminate one of the moons — either through the nuclear reactor on board, or through the terrestrial microbes that have been found to sometimes survive space voyages. While some fuel was still left, NASA decided to sacrifice Galileo rather than risk contamination.