By Paul Rincon
BBC News Online science staff
Just as excitement at the prospect of a successful British Mars landing with the Beagle 2 probe fades into distant memory, the UK may have found a new outer space pioneer to cheer on.
The Cassini orbiter will release Huygens to investigate Titan
The Cassini-Huygens mission to Saturn is often billed as a joint venture between the US, European and Italian space agencies. But the spacecraft has been assembled with extensive input from UK scientists and companies.
The £2bn mission consists of two main elements: the Cassini orbiter and the Huygens probe. Six out of the 12 instruments on Cassini and two out of the six instruments on Huygens were built with British involvement.
Cassini will enter orbit around Saturn on 1 July to begin a four-year study of the ringed planet, its complex magnetic environment and mysterious moons.
Six months later, it will release the piggybacked Huygens probe into the thick atmosphere of Saturn's moon Titan.
"It is far and away the most distant controlled descent and landing that has ever been attempted," said John Zarnecki of the Open University, principal investigator for Huygens' surface science package.
Huygens will be set free from Cassini on Christmas Day, a date that is all too familiar to those who followed Beagle's ill-fated attempt at landing on the Red Planet. The probe will plunge into Titan's atmosphere 20 days later at a speed of 7km/sec before opening parachutes to control its descent.
"I must point out that as a member of the Beagle team, I wish I could say that [Huygens] will be the second piece of UK hardware to land on a cosmic body; clearly that is now not the case."
A new hope
Professor Colin Pillinger, Beagle's lead scientist, was present at the London news conference to discuss the British effort on the Cassini-Huygens mission.
A thick, orange haze obscures Titan's surface, so what Huygens will land on is not certain. It could touch down on solid rock, squelchy goo, or an oily lake of methane and ethane.
For this reason, Zarnecki commented, the European Space Agency (Esa) prefers to call Huygens an atmospheric probe, not a lander. "Its survival on the surface is not guaranteed," Zarnecki explained.
But the team hope Huygens will remain operational long enough to transmit data on its surface environment to Cassini.
Titan will provide a unique opportunity to travel back in time. Conditions on the Saturnian moon today resemble Earth's own atmosphere billions of years ago, in which the chemical reactions necessary for the origin of life must have taken place.
Huygens is set for a white knuckle descent through Titan's atmosphere
This raises the question of whether primitive life might already be there. Huygens is able to characterise the chemistry of its surrounding environment, but the probe is not designed to look for life.
Furthermore, mission scientists made it clear that they do not expect to find any. It's far too cold on the surface of Titan, they agreed (about -179C). Although mission scientist Dr Carl Murray suggested life might be able to survive below the surface where it may be warmer.
However, it has also emerged that any life to be found on Titan after Huygens touches down might not be native. The craft is not sterile and may therefore deliver our terrestrial bugs to the surface of this distant world.
Recent pictures of the moon suggest there may be an icy continental land mass the size of Australia surrounded by seas of hydrocarbons.
Further imaging of Titan will help scientists better plan for Huygens' descent by determining wind speeds in the atmosphere.
Since April 2004, Cassini's images of Saturn have been more detailed than those of the Hubble Space Telescope.
"If the cameras were mounted on St Paul's Cathedral, they could resolve a one pence coin on top of the London Eye," Dr Murray explained. "They are the best ever cameras sent out into the Solar System."
Cassini will insert into a Saturn orbit on 1 July
These cameras will play a crucial role in solving some of the mysteries surrounding the formation and behaviour of Saturn's famous ring system.
"The rings are no more than 200 million years old. Either we're present at a very important point in time or we're just seeing the latest version of them," said Dr Murray.
Probing the unknown
So little is known about Saturn that for much of its four-year tour, the Cassini orbiter will be breaking into uncharted scientific territory.
"Saturn emits 80% more radiation than it receives from the Sun," said Dr Andrew Coates of the Mullard Space Science Laboratory in London.
"It's certainly not nuclear fusion going on in there. We think it's to do with helium raining down on the metallic hydrogen core. But we'll be able to test that with the Cassini orbiter."
Cassini will investigate Saturn, its rings and its magnetic field
High-speed winds in Saturn's atmosphere might also indicate a heat source within the gas giant, Dr Coates said.
These questions are part of the wider mystery surrounding Saturn's internal structure, a mystery Cassini is designed to unravel.
The orbiter will also investigate the complex configuration and behaviour of Saturn's magnetic field; the way it interacts with the solar wind, Saturn's moons and the planet's rings; and its relationship to radiation emissions from the gas giant.