NASA's $3.9 billion Cassini spacecraft completed its death plunge into Saturn on Friday, ending a fruitful 20-year mission to explore one of the solar system's most intriguing outer planets.

"The signal from the spacecraft is gone," said Earl Maize, Cassini mission manager, as the unmanned orbiter ran out of fuel and disintegrated in Saturn's atmosphere, as planned, in order to avoid damaging the planet's moons.

The end of the mission came at 7:55 am (1155 GMT), NASA said.