Cassini was deliberately flown into Saturn in September 2017 while still working perfectly, because the alternative was letting a dying spacecraft carrying Earth bacteria eventually drift into Enceladus, a moon with a liquid ocean and hydrothermal vents on its floor.

Cassini was deliberately flown into Saturn in September 2017 while still working perfectly, because the alternative was letting a dying spacecraft carrying Earth bacteria eventually drift into Enceladus, a moon with a liquid ocean and hydrothermal vents on its floor.

On 15 September 2017, Cassini entered Saturn’s atmosphere while eight of its instruments were still returning data. The spacecraft had not suffered a terminal failure. NASA sent it into the planet on purpose. The reason was not simply that a long mission needed a dramatic ending. Cassini was running low on the propellant required to control its trajectory. Once that control disappeared, the agency could no longer guarantee that the spacecraft wo…