Euro craft set for historic comet landing
A European probe was poised to land on a comet Wednesday, the climax in a historic quest to explore an enigma of the Solar System, mission control said.
After a trek lasting more than a decade and covering 6.5 billion kilometres (four billion miles), a mini lab called Philae separated from its mothership Rosetta, on schedule despite a last-minute glitch.
Philae was placed on course for landing on 67P/Churyumov-Gerasimenko, a comet now more than 510 million kilometres (320 million miles) from Earth and racing towards the Sun.
The lander "is now on its way to becoming the first spacecraft to touch down on a comet," the European Space Agency (ESA) said after separation.
The news met with applause at mission control in Darmstadt, Germany, breaking an anxious wait in this extraordinary, marathon mission.
Those gathered to witness the high-stakes landing were Ukrainian astronomers Klim Churyumov and Svetlana Gerasimenko, who discovered the comet in 1969.
The first post-separation signal from Philae was met with great relief over two hours after it ejected as planned.
Nerves were also stretched by a problem discovered overnight in Philae's landing equipment.
The washing machine-sized lander is meant to settle down on 67P at a gentle 3.5 kilometres per hour around 1530 GMT, firing two harpoons into a surface that engineers fervently hope will provide enough grip.
Ice screws at the end of its three legs will then be driven into the low-gravity comet to stop the probe bouncing back into space.
A routine check found an apparent malfunction with a small gas thruster on top of Philae which was meant to fire during landing to provide a downward push.
"We are going to have to depend entirely on the harpoons," said Stephan Ulamec from German aerospace firm DLR.
With just over an hour to go to scheduled landing, ESA director general Jean-Jacques Dordain reported: "So far so good" as the first photo taken by Philae of its mothership was shown to guests in Darmstadt to excited applause.
"We've had evidence of the separation, we had even the image and the sound and we know that the descent so far is as planned," he said.
A tweet from a special ESA Operations hashtag #CometLanding added: "Finally! I'm stretching my legs after more than 10 years. Landing gear deployed!"
"I don't have finger nails, so I won't be biting them," quipped ESA's senior science advisor, Mark McCaughrean.
If all goes according to plan, Earth will receive a signal at about 1600 GMT (11pm Thailand time) to say Philae has landed.
Comets are believed to be clusters of primordial ice and carbon dust left over from the building of the Solar System. They are doomed to circle the Sun in orbits that can range from a few years to millennia.
A 100-kilogramme (220-pound) robot lab, Philae was designed to piggyback comet "67P" and probe its chemistry and structure with 10 instruments.
With Philae riding piggyback, Rosetta was launched in 2004 for a decade-long journey that saw it enter the comet's orbit in August this year.
Astrophysicists hope Philae's examination of the icy dust cluster will unlock knowledge about the origins of the Solar System and even life on Earth.
A leading theory states that comets may have "seeded" the fledgling planet 4.6 billion years ago with life-giving carbon molecules and water.
From its vantage point in orbit of "67P", Rosetta has made some astonishing observations.
The comet's profile somewhat resembles that of a rubber bath duck -- but darker than the blackest coal, and with a surface gnarled and battered by billions of years in space.
If Philae comes to grief, scientists will be hugely disappointed although they note that Philae accounts for only about a fifth of the mission's total expected data haul.
Rosetta will continue to escort the comet, scanning it with 11 instruments as it loops around the Sun and makes its closest approach next year.