NASA's $3.9 billion Cassini spacecraft completed its death plunge into Saturn,  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 (12.55pm Irish time), NASA said.

Cassini was launched in 1997 and took seven years to travel two billion miles to Saturn, before embarking on a 13-year journey of discovery that delivered a wealth of scientific data on the planet and its moons.

Scientists lost contact as Cassini started to feel the effects of drag from Saturn's atmosphere and began to tumble, causing its dish antenna to lose sight of Earth.

It then burned like a meteor and tore apart and was completely consumed within minutes of the signal loss.

Its plunge to destruction marks the end of a series of 22 orbits that allowed the probe to slip between Saturn and its rings.

Because Saturn is so far away, the spacecraft's last gasp transmissions took 83 minutes to reach Earth.

Right up until it beamed its final signals to Earth eight of the spacecraft's 12 scientific instruments were gathering data from the top of Saturn's atmosphere and transmitting information about its structure and composition.

A high point of the mission came in January 2005 when a small European Space Agency lander called Huygens detached from Cassini and descended to the surface of Saturn's largest moon Titan.

The probe touched down on a pebble-strewn surface with the consistency of wet sand. It was the first successful landing on a world in the outer solar system.

Another key discovery made by Cassini was a global ocean under the icy surface of another moon, Enceladus, that may sustain life.

The decision to send Cassini to its fiery grave was taken in order to avoid any chance of the spacecraft crashing onto Titan or Enceladus and possibly contaminating the potentially life-hosting worlds with Earth bugs.