Top class images help ESA's Rosetta prepare to ride on a cosmic bullet

February 27, 2002

Paris, 26 February 2002

Chase a fast-moving comet, land on it and 'ride' it while it speeds up towards the Sun: not the script of a science-fiction movie, but the very real task of ESA's Rosetta spacecraft.

New observations with the European Southern Observatory's (ESO) Very Large Telescope (VLT) provide vital information about Comet Wirtanen - Rosetta's target - to help ESA reduce uncertainties in the mission, one of the most difficult ever to be performed.

Every 5.5 years Comet Wirtanen completes an orbit around the Sun. Wirtanen has been seen during almost all its apparitions ever since its discovery in 1948, but only recently have astronomers obtained detailed observations that have allowed them to estimate the comet's size and behaviour. The most recent of these observations was performed in December 2001 with the Very Large Telescope (VLT), located at the Paranal Observatory (Chile). As a result of these observations ESA will be able to refine plans for its Rosetta mission.

Rosetta will be launched next year and it will reach Comet Wirtanen in 2011. By that time the comet will be as far from the Sun as Jupiter, charging headlong towards the inner Solar System at speeds of up to 135,000 km/h. To get there and to be able to match the comet's orbit, Rosetta will need to be accelerated by several planetary swing-bys, after which the spacecraft - following a series of difficult manoeuvres - will get close to the comet, enter into orbit around it and release a lander from a height of about 1 km.

The VLT observations were planned specifically to investigate the activity of Wirtanen at the time of the landing manoeuvres. These observations have confirmed that - at the same distance from the Sun at which the landing will take place (450 million km) - the activity on Wirtanen is very low. This is very good news for the mission, because it means that there will not be so much dust ejected as to make the landing dramatically difficult.

Comets are basically small frozen bodies made of ice and dust. When they get close to the Sun the heat causes ices on the comet's surface to "evaporate", and gas and dust grains are ejected into the surrounding space forming the comet's atmosphere (coma) and the tail. In addition to dropping a lander on the comet's nucleus for detailed in-situ observations, Rosetta's task is to investigate the evolution of the comet on its way to the Sun: in fact, Rosetta will keep orbiting around Wirtanen up to the end of the mission in July 2013, at which time the comet is at its closest approach to the Sun, at about 160 million km from it.

VLT observations have also provided Rosetta mission planners with an accurate measurement of their target's size: Wirtanen is only 1.2 km in diameter, a true cosmic bullet.

"Rosetta is certainly a very challenging space mission. No one has ever tried to land on a comet before," says Gerhard Schwehm, Rosetta's Project Scientist. "We need to learn as much as possible about our target. The new data will allow us to improve our models and make decisions once we get there."

Note to editors

Rosetta's prime scientific goal is to unravel the origin of the Solar System. The chemical composition of comets is known to reflect that of the primordial nebula that gave birth to the Solar System - in the planets, that primeval material has gone through complex processing, but not in the comets. Therefore, Rosetta will allow scientists to look back 4.6 billion years, to an epoch when the Solar System formed.

Previous studies by ESA's Giotto spacecraft and by ground-based observatories have shown that comets contain complex organic molecules - compounds that are rich in carbon, hydrogen, oxygen and nitrogen. Intriguingly, these are the elements which make up nucleic acids and amino acids, essential ingredients for life as we know it. Did life on Earth begin with the help of comet seeding? Rosetta may help us to find the answer to this fundamental question.

Rosetta carries 21 experiments in total. These are provided by scientific consortia from institutes across Europe and the United States.

The Wirtanen observations by the VLT fall into a tradition of fruitful collaboration between the European Space Agency (ESA) and the European Southern Observatory (ESO). The two organizations are already combining their efforts in several strategic areas, in order to facilitate the synergy between space and ground facilities, where mutual sharing of technology and procedures can result in substantial savings.

For more information please contact:

ESA - Communication Department
Media Relations Office
Paris, France
Tel: +33 (0)1 5369 7155
Fax: +33(0)1 5369 7690

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