Ten years in the making and costing a billion euros, the unmanned craft Rosetta will take off from an Ariane 5 launcher on Thursday for a 10-year space odyssey.

"This is going to be the ultimate cometary mission," the European Space Agency's director of science, David Southwood said.

"It will underpin cometary science for the next decade."

Science fiction

The endeavour has been likened to science fiction, for the probe will have to travel five billion km to rendezvous with its target, the comet Churyumov-Gerasimenko, 675 million km from the Sun.

After firing its thrusters to close on the target, in November 2014, Rosetta will send down a tiny robot lab, Philae, that will gently land on the surface of the "C-G" comet and carry out an ambitious programme to assess the comet's geology as the spacecraft heads around the Sun.

"This is going to be the ultimate cometary mission"

David Southwood
Director of Science, European Space Agency



Equipped with 21 instruments to map, sound and probe, Rosetta and Philae hope to find what comets are made of.

The answer, according to astrophysicists, could shed light on how life began on Earth.

For space scientists, comets are the most primitive material left over from the making of the Solar System some 4.6 billion years ago.

Great expectations

Barely touched by gravity and heat, strangely black inspite of their icy surface, extraordinarily light in density, comets may contain volatile and complex molecules, some experts believe.

These molecules may have been the chemical kick to start life on Earth, according to the so-called "panspermia" theory.

It postulates that the Earth, in its infancy, was bombarded with comets and asteroids, whose elements reacted with the oceans to provide the building blocks for DNA.

"This mission has the potential to make spectacular discoveries about the origin of Earth and, perhaps, about the origin of life itself," Jean-Pierre Bibring of the France's National Centre for Space Studies, said.

The minutest error in navigation will send the mission hurtling out of the Solar System, for the spacecraft has to meet up with an object just four kilometres wide.