Launch

The European Space Agency's (ESA) Rosetta cometary probe was launched successfully on a Ariane 5 rocket at 07.17 GMT on 2 March 2004. The probe will fly around the Sun before returning to perform three flybys of the Earth and one of Mars finally reaching the comet 67P/Churyumov-Gerasimenko in 2014. During this journey, Rosetta will pass close to at least one asteroid.

Artist's impression of Rosetta dropping a lander onto a comet for the first time© ESA/AOES Medialab The final flyby of Earth in November 2009 will send Rosetta toward the orbit of comet. By mid-2011 the probe will be about 800 million km from the Sun, will fire its main engine and begin its manoeuvre intercept the comet.

It will be re-activated again in January 2014 as it enters the approach phase. Rosetta will close in on the nucleus of the comet over the following six months. The comet will be far from the Sun and its nucleus should be dormant, allowing a lander to be placed on the surface.

During the remainder of 2004, the spacecraft's onboard systems will be checked and its science payload will be commissioned. It will then be put into hibernation for the majority of its ten-year journey, although its systems will be re-activated during the planetary flybys.

ESA's Director General Jean-Jacques Dordain said during the launch:

After the recent success of Mars Express, Europe is now heading to deep space with another fantastic mission. We will have to be patient, as the rendezvous with the comet will not take place until ten years from now, but I think it's worth the wait.

Rosetta was due to launch on 23 January 2003. However the previous failure of an Ariane 5 launcher led ESA to postpone the launch. As a result, Rosetta would not be able to study its original target, comet Wirtanen, as it will be out of range.

The Rosetta team had to identify a new target and a new launch date was set to intercept the comet 67P/Churyumov-Gerasimenko.

Background

Artist's impression of the Rosetta orbiter and lander approaching a comet© ESA Rosetta's mission is to study the surface of a comet at close range. It will carry out detailed observations of the nucleus of the comet and analyse material collected from the surface by the lander.

Just as the Rosetta Stone was the 19th century key to understanding Egyptian hieroglyphs, it is hoped that the Rosetta spacecraft might answer some of today's unanswered questions about comets.

Rosetta specifically aims to establish how much a comet weighs; if the nucleus of a comet is a single piece or consists of loosely joined blocks, and the chemical composition of the comet itself. There are also questions about the physical features of comets, such as why the nucleus is so dark and why small regions are highly active when the majority of the surface is not.