The Grand Finale of Cassini: Saturn, 2017
2017 · event
On 15 September 2017 the spacecraft Cassini turned its antenna toward the Earth, entered the upper atmosphere of Saturn and burned up while still transmitting. The end had been chosen deliberately. The spacecraft was running out of fuel, and mission planners refused to risk an uncontrolled crash onto Enceladus or Titan, moons that Cassini itself had shown might be capable of supporting life. The last signal took eighty three minutes to cross the distance and arrived after the spacecraft had already ceased to exist.
Cassini had launched in 1997 and reached Saturn in 2004, a joint undertaking of the American, European and Italian space agencies. In January 2005 it released the European probe Huygens, which parachuted through the orange haze of Titan and landed on a plain of rounded pebbles, the first landing ever made in the outer solar system.
Over thirteen years in orbit the spacecraft rewrote the textbook. It found geysers of water erupting through cracks at the south pole of Enceladus, evidence of a global ocean beneath its ice, with salts and organic molecules in the plume. On Titan it mapped lakes and rivers of liquid methane, the only stable surface liquid known outside the Earth. It watched a giant storm circle Saturn, tracked the seasons on the rings and discovered new moons.
The final months were designed as a last experiment. Cassini flew twenty two times through the narrow gap between Saturn and its rings, a region no spacecraft had entered, measuring the planet's gravity and magnetic field and the mass of the rings themselves. The mission is remembered as much for its ending as for its findings, a machine sent into a planet in order to protect the places it had found.