Space probe Cassini plunges to destruction through Saturn's atmosphere

At 12.56 pm UK time radio contact with the 22ft long nuclear-powered probe was lost as Cassini tumbled to its doom 930 miles above Saturn's cloud tops.

Plummeting at 77,000mph, in seconds it disintegrated into fragments and burned up.

Mission controllers at Nasa's Jet Propulsion Laboratory in Pasadena, California, clapped and hugged each other when the signal loss was confirmed.

Project manager Earl Maize said: "Congratulations to you all. This has been an incredible mission ... you're all an incredible team."

The decision to kill off Cassini was taken because the craft would soon run out of fuel and become impossible to steer.

Scientists feared a collision with Titan or Enceladus, two of Saturn's moons that in the past 10 years have shown a potential to host simple life.

Safe disposal of Cassini was seen as the best way to avoid the remote possibility of contaminating the pristine moons with Earth bugs.

The space craft, launched from Cape Canaveral, Florida, in 1997, took seven years to reach Saturn and was originally intended to explore the planet and its moons for just three years.

In the end its life was extended by another decade.

The space mission is regarded as one of the most ambitious and successful ever undertaken. For some scientists, including a large team from the UK, it has taken up whole careers.

One of Cassini's most important discoveries was the existence of a global watery ocean under the icy surface of Enceladus that could conceivably harbour life.

A European Space Agency probe carried by the orbiter, called Huygens, made headlines around world when it landed on Saturn's largest moon Titan in January 2005.

Together Cassini and Huygens showed Titan to have a startlingly Earth-like landscape, with rivers, lakes and seas filled with liquid methane and ethane.

Scientists believe Titan's "pre-biotic" environment could also support life, but not necessarily as we know it.

Cassini has also discovered seven new moons, six of which have been named, observed raging storms on Saturn, and shed new light on the planet's famous rings.

The space craft's fate was sealed on September 11 when it was sent on a final fly-by of distant Titan, 760,000 miles from Saturn. Titan's gravity nudged it onto a course back to Saturn from which there would be no return. Scientists nicknamed it the "goodbye kiss".

Right up until it radio contact was lost Cassini was sending back data to Earth in near-real time.

The last images of looming Saturn were captured by the probe several hours earlier as it headed towards the planet.

For a brief time Cassini's instruments sampled gases and molecules from Saturn's atmosphere, transmitting data that could not be obtained by remote sensing alone.

Buffeted by strong winds, the probe fired its attitude thrusters to maintain stability. Cassini struggled on for about a minute longer than forecast but when its dish antenna failed to lock onto Earth, radio contact was lost.

Because of the length of time it takes radio waves to cross the enormous gulf between Saturn and Earth, mission controllers only confirmed signal loss 83 minutes after it happened.

By then, Cassini had already been turned into a fireball and vaporised.

Royal Astronomical Society president Professor John Zarnecki, who worked on Cassini/Huygens for more than 20 years, said: "Of course I feel slightly sad. But it's given me the most wonderful ride and it delivered my instrument to the surface of Titan where it's still sitting.

"It has shown Titan to be even more wonderful than we had ever imagined - we've seen seas and lakes and rivers and dune fields and clouds and rain and more.

"The data we collected is unlikely to be bettered for many decades to come. The mission has not only been a wonderful scientific success but has also shown what can be achieved when scientists and engineers from across the world can work together with a common purpose to realise lofty goals."

Prof Zarnecki was a planetary scientist at the Open University before becoming director of the International Space Science Institute in Berne, Switzerland.

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Cassini's death plunge was the climax of a "grand finale" that saw the probe slip between Saturn and its rings in 22 daring orbits.

Fifteen minutes before the end, the voice of Dr Maize could be heard in a live stream from mission control telling his team: "This might be a good time to pass out the farewell peanuts."

Earlier Jet Propulsion Laboratory director Mike Watkins told a Nasa interviewer: "It's kind of a bitter-sweet event for all of us.

"For me personally, it's more sweet than bitter, because Cassini has been such a fantastic mission.

"Most of what we have in science books about Saturn comes from Cassini.

"Part of what makes the end of Cassini sweet is that the discoveries are so compelling we have to go back.

"They're just ground-breaking."

Other British Cassini scientists paying tribute to the mission included Professor Simon Green, from the Open University, who said: "The scientific legacy of the mission will extend long beyond its fiery end in the clouds of Saturn."

Dr Leigh Fletcher, from the University of Leicester, said: "Cassini-Huygens will truly be the benchmark against which all future missions are compared."

Professor Andrew Coates, head of the planetary science group at University College London's Mullard Space Science Laboratory, called Cassini "one of humankind's great voyages of discovery".

He added: "The mission has changed the way we think of where life may have developed beyond our Earth."

Astronomer Royal Professor Sir Martin Rees, who did not play a part in the mission, said: "We've now reached the grand finale of what's surely one of the greatest scientific and engineering achievements in space exploration.

"Cassini has given us a cornucopia of information about Saturn, its rings and its moons."

He added it was "amazing" that Cassini had achieved so much with 1990s-era technology.

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