PARIS - The space probe Rosetta on Wednesday made a historic rendezvous with a comet, climaxing a 10-year, six-billion-kilometre (3.7-billion-mile) chase through the Solar System, the European Space Agency (ESA) said.
"We're at the comet," Rosetta's flight operations manager, Sylvain Lodiot, declared in a webcast from mission control in Darmstadt, Germany.
It marks the first time a spacecraft has been sent into orbit around a comet, a wanderer of the Solar System whose primeval dust and ice may hold insights into how the planets formed.
In November, a robot scientific lab called Philae will be sent down to the surface to make the first-ever landing on a comet.
Rosetta's rendezvous with Comet 67P/Churyumov-Gerasimenko was confirmed at 0929 GMT at distance of 400 million km from Earth, according to signals received at ground stations.
ESA Director General Jean-Jacques Dordain hailed the fruit of 20 years' work to design, build and launch the three-tonne craft and then steer it to a tiny target in deep space.
"It makes 2014 the year of Rosetta," he said.
"Rosetta is a unique mission, unique by its scientific goal," Dordain said. "Understanding our origins is certainly the best way to understand our future."
On its Twitter page, the Rosetta mission said "Hello, comet!" in the languages of the agency's 20 nations.
"It's a historic meeting and a great first in world science, which the global space community has been awaiting for a decade," said Jean-Yves Le Gall, president of France's National Centre for Space Research (CNES), a major contributor to the project.
ESA showed a close-up picture of a gnarled, greyish object, comprising two lobes joined by a neck. The surface is pucked by what seems to be impact marks.
"Our first clear views of the comet have given us plenty to think about," project scientist Matt Taylor said.
"Is this double-lobed structure built from two separate comets that came together in the Solar System's history, or is it one comet that has eroded dramatically and asymmetrically over time?"
Launched in March 2004, Rosetta had to make four flybys of Mars and Earth, using their gravitational force as a slingshot to build up speed to catch up with its prey.
It entered a 31-month hibernation as light from the distant Sun became too weak for its solar panels. That period ended in January with a wake-up call sent from Earth.
It then began a complex series of manoeuvres to slow down to walking speed with the comet.
If any one of those operations had failed, the probe would have gone whizzing past its target.
The final manoeuvre was a small firing of thrusters, lasting just six minutes and 26 seconds, it said.
"This burn will tip Rosetta into the first leg of a series of three-legged triangular paths about the comet," ESA said.
The "pyramidal" track placed the craft at a height of about 100 kilometres (60 miles) above the comet, said Lodiot.
Each leg of the triangle will be around 100 kilometres and take Rosetta between three and four days to complete.
Rosetta will gradually reduce its height, entering gravitational orbit in September.
Comets are believed by astrophysicists to be ancient ice and dust left from the building of the Solar System around 4.6 billion years ago. This cosmic rubble is the oldest, least touched material in our stellar neighbourhood.
Understanding its chemical ID and physical composition will give insights into how the planets coalesced after the Sun flared into light, it is hoped.
It could also determine the fate of a theory called "pan-spermia," which suggests comets, by smashing into the infant Earth, sowed our home with water and precious organic molecules, providing us with a kickstart for life.
The spacecraft is named after the famous stone, now in the British Museum, which explained Egyptian hieroglyphics, while its payload, Philae, is named after a Nile obelisk that in turn helped decipher the Rosetta stone.
The four-kilometre comet returns around the Sun on an egg-shaped orbit every six and a half years, its furthest point being beyond Jupiter.
It is named after two Ukrainian astronomers, Klim Churyumov and Svetlana Gerasimenko, who first spotted it in 1969.