All systems go for historic comet landing

The European Space Agency (ESA) ordered a probe to attempt Wednesday the first landing on a comet and investigate one of the great mysteries of the Solar System.
      
"We've got the final go" for the operation, an ESA spokeswoman said at mission control in Darmstadt, Germany.
      
Philae, a robot lab bearing 10 instruments, will be ordered to separate from its mother ship Rosetta at 0835 GMT, the agency said, after the last of four checks.
      
Half a billion kilometres (300 million miles) from Earth, it will descend towards Comet 67P/Churyumov-Gerasimenko, racing towards the Sun.
      
"Final Go/NOGO complete! We're GO for separation!!!," the Rosetta mission said in a tweet.
      
If all goes well, Philae will touch down about seven hours later before carrying out scientific experiments on its surface -- a double first in space history.
      
Conceived in the 1980s, the Rosetta mission seeks to reveal secrets about the origins of the Solar System and maybe even life on Earth.
      
The 1.3-billion-euro ($1.6-billion) project was approved in 1993.
      
Rosetta, carrying Philae, was hoisted into space in 2004, but needed more than a decade to reach its target in August this year -- a six-billion-kilometre (3.75-billion-mile) trek around the inner Solar System.
      
Turning slowly around "67P" since its rendezvous, Rosetta has made some astonishing observations.
      
The comet's profile somewhat resembles that of a rubber bath duck -- but a 'toy' darker than the blackest coal, and gnarled and battered from billions of years in space.
      
It has a treacherous, irregular surface, with crags, cliffs and rocks -- an extremely difficult target to land on.