AT A GLANCE

TIMELINE: Cassini rocketed from Cape Canaveral, Florida, on Oct. 15, 1997, carrying with it the European Huygens lander. The spacecraft arrived at Saturn in 2004. Six months later, Huygens detached from Cassini and parachuted onto the giant moon Titan.

Cassini remained in orbit around Saturn, the only spacecraft to ever circle the planet. Last April, NASA put Cassini on an ever-descending series of final orbits, leading to Friday’s swan dive. Better that, they figured, than Cassini accidentally colliding with a moon that might harbor life and contaminating it.

SPACECRAFT: Traveling too far from the sun to reap its energy, Cassini used plutonium for electrical power to feed its science instruments. Its separate main fuel tank, however, was getting low when NASA put the spacecraft on the no-turning-back Grand Finale.

RINGS: Cassini discovered swarms of moonlets in Saturn’s rings, including one called Peggy that made the short list for final picture-taking. Scientists wanted one last look to see if Peggy had broken free of its ring. Data from the spacecraft indicate Saturn’s rings—which consist of icy bits ranging in size from dust to mountains—may be on the less massive side. That would make them relatively young compared with Saturn; perhaps a moon or comet came too close to Saturn and broke apart, forming the rings 100 million years ago.

MOONS: Saturn has 62 known moons, including six discovered by Cassini. The biggest, by far, is the first one discovered way back in the 1655: Titan, which slightly outdoes Mercury. Its lakes hold liquid methane, which could hold some new, exotic form of life. Little moon Enceladus is believed to have a global underground ocean that could be sloshing with life more as we know it.