Robot heads towards comet surface

Europe's audacious bid to put a robot on the surface of a comet is under way.

At 08:35 GMT, the Rosetta satellite released its Philae lander towards Comet 67P/Churyumov-Gerasimenko, a large mass of ice and dust some 510 million km from Earth.

The descent should take seven hours, with a signal confirming touchdown received at Earth at around 16:00 GMT.

Success would be a first for space exploration - no mission has previously made a soft landing on a comet.

Part of the difficulty is the very low gravity on the 4km-wide ice mountain.

Philae needs to be wary of simply bouncing back into space.

As a consequence, on contact it will deploy foot screws and harpoons to try to fasten its position.

It will then take a picture of its surroundings - a strange landscape containing deep pits and tall ice spires.

This is, though, an event with a highly uncertain outcome.

BBC