European scientists were preparing for a historic rendezvous on Wednesday between a comet and a space probe after a 10-year, six billion-kilometre (3.7-billion-mile) chase through the Solar System.
The scout Rosetta is on track for meeting Comet 67P/Churyumov-Gerasimenko in deep space, when it will become the first envoy of Man to orbit one of these wanderers of the Solar System, they said.
If all goes well, the mission in November will carry out the first landing on a comet.
Rosetta will send a robot chemistry lab to the surface to delve into a theory that comets hold the key to understanding how our star system formed.
"After completing a complex series of nine orbital manoeuvres since the end of hibernation on January 20, Rosetta is finally in position to rendezvous with the comet," the European Space Agency (ESA) said on Tuesday.
Orbital entry will be triggered by a small firing of her thrusters, lasting just six minutes and 26 seconds, starting at 0900 GMT on Wednesday, it said.
"This burn will tip Rosetta into the first leg of a series of three-legged triangular paths about the comet," it said.
Top officials from ESA will be at mission control in Darmstadt, Germany, waiting for the signals to start and stop this crucial final operation to be safely received by ground monitoring stations, 22 minutes later.
The "pyramidal" orbits will put the craft at a height of about 100 kilometres (60 miles) above the comet, said Sylvain Lodiot, Rosetta's flight operations manager. Each leg of the triangle will be around 100 kilometres and take Rosetta between three and four days to complete.
The arrival will mark a key moment of the boldest project ever undertaken by ESA -- a 1.3-billion-euro ($1.76-billion) investigation into one of enigmas of the Solar System.
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.
- Navigational feat -
Rosetta is poised to meet up with Comet "C-G" more than 400 million kilometres from where it was launched.
Getting there has been an unprecedented navigational exploit.
Launched in March 2004, the three-tonne craft has had to make four flybys of Mars and Earth, using their gravitational force as a slingshot to build up speed.
It then 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.
The spacecraft is named after the famous stone, now in the British Museum, that explained Egyptian hieroglyphics, while its payload Philae is named after an obelisk that in turn helped decipher the Rosetta stone.
The four-kilometre comet is named after two Ukrainian astronomers who first spotted it in 1969.
Source: AFP