The ceremonial unveiling was also witnessed by representatives of the Particle Physics and Astronomy Research Council (PPARC), which funds the UK contribution to the Rosetta mission, members of the media, and more than 100 scientists and engineers from around the world.

"The expertise of European scientists in cometary exploration has been absolutely outstanding, from the early days of astronomy with Halley and Newton, through to Ludwig Biermann who discovered and explored the solar system and its interaction with comet tails." said Prof. Bonnet. "Then Giotto flew to Halley's Comet 13 years ago. Now we have Rosetta, which builds on this experience."

The Rosetta Spacecraft

The mission involves two spacecraft -- a 3 tonne orbiter, which will fly alongside Comet Wirtanen's icy nucleus, and a small lander, which will touch down on the nucleus itself. The Rosetta orbiter will carry 12 scientific experiments, with a further nine on the lander.

A 1:4 scale model was chosen for today's unveiling because of the impossibility of finding a venue large enough to contain the full-size version. The flight model of the Rosetta Orbiter spacecraft is 32 metres across, so large that it would stretch the entire width of a football pitch. Since Rosetta will have to operate more than 720 million km (450 million miles) from the Sun, where light levels are only 4% of those on the Earth, it has to carry giant solar panels to provide electrical power in the dark depths of the Solar System.

One of the main themes of the event was the importance of Rosetta as a Cornerstone mission in ESA's Horizons 2000 science programme. "Rosetta is a flagship mission for European solar system exploration. It is one of four missions that will land on a foreign body in the first 10 years of the next century. ESA spacecraft will lead the way with landings on Mercury, Saturn's moon Titan, and even on a comet", said Prof. Bonnet.

Speakers also explained that, apart from its scientific importance, Rosetta is also a significant source of technological innovations which can be used for other missions such as Mars Express. This enables ESA to make efficient use of resources and reduce development costs for other science projects.

"Rosetta will be a tremendous technological challenge," said Project Manager Bruno Gardini. "We have less than four years to build the largest, most sophisticated spacecraft ever to visit a comet."

"There are many challenges ahead," he added. "Rosetta will have to survive a hazardous eight year trek across 5.25 billion km of space. It will then have to rendezvous with a comet which is travelling towards the Sun at over 130,000 km per hour. After releasing a lander onto its tiny nucleus, it will have to fly alongside the comet as it swoops towards the Sun."

The Rosetta Mission

Although ESA's Giotto spacecraft flew past two comets in 1986 and 1990, many questions remain unanswered. Rosetta is designed to unravel the mysteries surrounding these primitive objects.

"Space exploration is all about discovering the unknown," commented Rosetta Project Scientist, Dr. Gerhard Schwehm. "Just as, 200 years ago, the discovery of the Rosetta Stone eventually enabled Champollion to unravel the mysteries of ancient Egyptian hieroglyphics, so Rosetta will help scientists to unravel the mysteries of comets."

Dr. Schwehm went on to explain that comets are among the oldest, and least altered, objects in the Solar System. They are thought to have existed, almost unchanged, for the last 4.5 billion years, and are regarded as the building blocks from which the planets formed.

Comets are also important sources of information for scientists studying how our planet evolved and life began. One theory suggests that a comet collision wiped out the dinosaurs 65 million years ago. Such impacts were much more frequent when the Earth was young. It seems that comets arrived in such vast numbers that they may have delivered a significant fraction of the water in our oceans. Furthermore, some scientists believe that the organic (carbon-based) molecules found in comets were the 'seeds' from which life evolved on Earth 4 billion years ago.

Dr. Alan Fitzsimmons of Queen's University, Belfast, commented, "Through PPARC, the UK is funding the Open University's MODULUS instrument on board Rosetta and also supporting the Plasma Science Package. This will allow European scientists to decipher the physics and chemistry of comets in unprecedented detail, and ensures that the UK plays a key role in this exciting mission."

Rosetta and the British Museum

ESA's comet chasing spacecraft is named after the Rosetta Stone, one of the most famous exhibits at the British Museum. Starting on 10 July, the Rosetta Stone will be the centrepiece of the Museum's exciting new 'Cracking Codes' exhibition. Hundreds of thousands of visitors from around the world are expected to flock to this exhibition during the next six months. Models of the Rosetta Orbiter and Lander will be on display throughout the event.

"The Rosetta Stone has been described as the most famous piece of rock in the world, and is one of the most visited objects in the British Museum," said Dr. Richard Parkinson of the Museum's Department of Egyptian Antiquities. "This month marks the 200th anniversary of its discovery by Napoleon's troops at Rosetta in Egypt. The Museum is celebrating the event with a revolutionary redisplay of the newly conserved stone, and a special exhibition, entitled `Cracking Codes', to show the full impact of the Stone on our understanding of the past."

"The use of the stone for decipherment of Ancient Egyptian was not a single event but a continuing process of scientific investigation. This is why we are particularly delighted to be able to include a model of the Rosetta space probe to show how decipherment is very much to do with the future and not just with the past," he added.

The Return of Giotto

Today's press briefing coincided with the London meeting of the Rosetta Science Working Team and the second Earth flyby of ESA's remarkable Giotto comet probe. Giotto's brief homecoming took place almost 14 years to the day since its launch on 2 July 1985 and five years after its previous return to Earth's vicinity on 2 July 1990.

Despite a peppering from dust particles travelling faster than bullets, Giotto survived its encounter with Comet Halley to return the first detailed, close-up pictures of a comet nucleus. Six years later, the remarkably robust spacecraft made history once more when it visited a second comet.

During today's flyby, the now deactivated spacecraft swept to within 220,000 km of the planet (just over half the Earth-Moon distance). Travelling at a speed of about 3.5 km/s, Giotto's trajectory took it over the South Pole and southern South America before it headed once more into deep space.

"Giotto paved the way for Rosetta," said Gerhard Schwehm. "It was the Agency's first planetary mission and was a tremendous success, both technically and scientifically. It provided a wealth of scientific results and gave scientists the unique chance to study two different comets with the same set of instruments."