A spacecraft the size of a small bus ended a seven-year, 3,2-billion kilometre journey and began a new era of exploration on Thursday morning as it sped over gas giant Saturn, and sent back the first closeups of the rings which have tantalised astronomers for four centuries.
The pictures from Cassini-Huygens were no more than hasty snaps — dark, grainy, and brief, snatched as the spaceprobe slowed to join Saturn’s retinue — but they were the first glimpse in more than two decades of these orbiting hoops of ice and rubble, about a kilometre thick but flaring out into space for 300 000km. The images were hailed by triumphant scientists 1,494-billion kilometres away in the US, Britain and Europe as a signal for the great adventure about to begin.
Cassini will undertake a series of 76 huge, swooping orbits that will take it past nine of Saturn’s 31 moons, in and out of the powerful magnetic bubble created by a mysterious dynamo at Saturn’s heart. In January, the United States spacecraft Cassini will relay data as it drops its European passenger Huygens on a suicide plunge to the surface of Titan, the only moon in the solar system with an atmosphere.
”More than 20 years have passed since Pioneer 11 and the Voyagers gave us a first glimpse of Saturn, as they crossed this complex system in only a few days,” said David Southwood, chief of science at the European Space Agency, and also one of the principal mission scientists.
”Now, with Cassini, we are here to stay, watch and investigate. And with Huygens we will go even deeper and further, not only plunging into an extraterrestrial atmosphere but also an atmosphere like the early Earth’s. This means we are travelling billions of years back into our own past to investigate one of the universe’s best-kept secrets: where we came from.”
Planning began 22 years ago. Cassini-Huygens is a 21st century mission built with 1990s technology to answer questions first posed in the 1980s. Many of the mission scientists began designing instruments for the spacecraft eight years before the giant plutonium-powered spaceprobe and its sophisticated lander Huygens was launched in 1997.
It had to loop around Venus, Earth and Jupiter to pick up speed by gravity slingshot manoeuvres before it could complete its jour ney. Researchers from Nasa, the European Space Agency and the Italian Space Agency — the three partners in the mission — cheered at the headquarters in California as they got the signal on Thursday morning that Cassini had passed through a gap in the planet’s rings, fired its engine for 95 minutes and slowed to become just another moon in the Saturnian system, precisely to a timetable first calculated almost a decade ago.
”We didn’t expect anything less and couldn’t have asked for anything more from the spacecraft and the team,” said Robert Mitchell, of the Jet Propulsion Laboratory in Pasadena. John Zarnecki, of the Open University, added: ”For me it’s been seven years in the planning, seven years of travel and 95 minutes of purgatory — but now we’ve made it and the next stop is Titan.”
Andrew Coates, of the Mullard Space Laboratory, of University College London, said: ”I’ve waited 15 years for this moment, and now our four-year tour of discovery can really begin.”
Saturn is the sixth planet from the sun, and the second largest in the solar system, after Jupiter.
The strange discs of closely packed ice and fragments of rock that form its rings serve as a miniature model of the disc of gas and dust around the early sun, five billion years ago, which condensed to form the nine planets. So a journey to Saturn is a journey into cosmic history. Some of Saturn’s moons are huge landscapes of ice, some of rock, and one of them, Titan, is wreathed in thick clouds of nitrogen, methane and ethane.
The first fruits of the mission, released on Thursday, were little more than postcards home: proof that the cameras worked and the spacecraft could transmit data. They were taken after Cassini sped through a huge gap between two of the outer rings, and began to slow down on the dark side, passing to within 12,000 miles of Saturn’s cloud tops before diving out through the same gap on the far side and back into the sunlight and contact with Earth almost a billion miles away.
”We were expecting it to be dark and had to take short exposures to make sure there was no smear. But the camera pointed where it was supposed to point. Everything seems to be just as we expected,” said Carl Murray of Queen Mary College, University of London, one of the camera team.
”This is a remarkable achievement and a wonderful example of a successful, international collaboration. The arrival of the Cassini-Huygens spacecraft at Saturn heralds a new age in our understanding of this majestic planet and its retinue of moons and rings. I have no doubt that the wealth of data to be returned will also provide unique insights into the origin and evolution of planetary systems. The next four years will be tremendously exciting for everybody.”
Future missions
July 10 2004: Aura satellite takes off from California to begin the most sophisticated ”health check” so far on the planet’s atmosphere
July 26: China launches the second of two satellites with European instruments to study the Earth’s magnetosphere
August 2: Messenger takes off from Cape Canaveral to explore Mercury for the first time in 30 years
Autumn: Cosmos 1, the first solar sailor, will be launched by a US consortium from a Russian nuclear submarine to test lightweight sails driven by the ”wind” from the sun
September 8: Genesis spends 884 days trapping bits of the sun fired from solar eruptions. It will drop them in a special capsule over Utah, to be caught by helicopter
December 25: Huygens probe separates from Cassini and both head for Saturn’s moon Titan
December 30: Deep Impact takes off from Florida to encounter Comet Tempel 1, and blow a hole the size of a football stadium in the comet’s surface in July 2005
January 14 2005: Huygens makes a slow suicide plunge through the dense hydrocarbon clouds of Titan — and is dead before its first signals reach Earth. – Guardian Unlimited Â