What will Rosetta spacecraft do?

Scientists are poised for a key moment in the history of space exploration when a spacecraft attempts to rendezvous with a comet on Wednesday.

Rosetta was launched 10 years ago, and is now edging closer to a comet known as 67P.

It will then attempt something unprecedented - going into orbit around the comet as it hurtles through space at 34,000 mph (55,000 km/h).

Science Editor David Shukman explains what Rosetta's mission will entail and what scientists hope it will discover.