Cassini skimmed closer than any previous spacecraft to the sixth planet from the Sun, and lived to tell the tale, sending back a signal that arrived early Thursday at 0656 GMT, about 20 hours after the crossing took place.
"No spacecraft has ever been this close to Saturn before. We could only rely on predictions, based on our experience with Saturn's other rings, of what we thought this gap between the rings and Saturn would be like," said Cassini project manager Earl Maize of NASA's Jet Propulsion Laboratory in Pasadena, California.
The gap between the rings and the top of Saturn's atmosphere is about 1,500 miles (2,400 kilometers) wide.
The rings are made of fast-moving particles of ice and space debris that could strike and disable the spacecraft.
Its next pass is scheduled for May 2.
The spacecraft is a joint mission of NASA, the European Space Agency and the Italian Space Agency. It launched in 1997 and has been orbiting Saturn since 2004.
Cassini is now running low on fuel and scientists have decided to end its mission rather than risk damaging one of Saturn's moons, whose subsurface oceans may be explored for signs of life in the future.