Rosetta: Comet Probe Beams Back Pictures

Mission control has said the Philae probe is descending on the right track as the touchdown window opens for its daring attempt to land on a speeding comet.

News of whether it has docked successfully is expected at around 4pm UK time.

There were cheers and hugs in the European Space Agency (ESA) control room when the probe's detachment from the Rosetta orbiter was confirmed shortly after 9am.

The agency tweeted : "SEPARATION CONFIRMED #SEP ESA confirms @Philae2014 Lander has separated from @ESA_Rosetta. Lander now enroute to #CometLanding".

The first signal from the detached lander came two hours later, but scientists have admitted the rock's surface appears more challenging that expected.

Philae has now deployed its landing gear and is ready to fire harpoons and latch on to the giant ball of dust and ice.

ESA released a picture from Philae as it detached from the Rosetta orbiter, and another from Rosetta showing Philae as it drifted away in the distance.

The landmark mission, which hopes to become the first to dock with a comet, is taking place 315 million miles from Earth as the rock hurtles through space at around 34,000mph.

Scientists also said they were surprised to find the rock was "emitting a song".

The Rosetta Plasma Consortium (RPC) said it believed the comet was releasing particles into space which were becoming electrically charged and causing fluctuations in its magnetic field.

To make it audible to humans, the signal has been boosted by a factor of about 10,000.

"This is exciting because it is completely new to us. We did not expect this and we are still working to understand the physics of what is happening," said the RPC.

The Philae lander is also preparing to drill 'ice screws' from each of its feet to stay fixed to the speeding rock.

Gravity on the comet is 100,000 times weaker than on Earth, so the potential for 'bounce-back' is a major challenge.

The probe, roughly the size of a dishwasher, is descending at walking pace and the final descent for the £1bn mission will take seven hours.

The mission is designed to analyse the composition and density of a comet to better understand the origins of our solar system.

However, a problem with the lander's active descent system emerged overnight and for a while put the final approach in jeopardy, the ESA revealed.

The thruster, meant to help counteract any rebound at touchdown, could not be activated.

Latching onto the comet will now depend completely on the harpoon and ice screw system, according to the space agency.

"We’ll need some luck not to land on a boulder or a steep slope," said Lander Manager Stephan Ulamec.

When it touches down on the 2.5 mile-wide comet - called 67P/Churyumov-Gerasimenko - the lander will use 10 sets of instruments to investigate the environment, including a probe to pierce the crust and take samples.

The Rosetta mission blasted off from French Guiana in March 2004 and has travelled more than four billion miles to reach its target.

Scientists used gravity to act as a catapult, plotting co-ordinates which took the orbiter around the Earth three times and Mars once.

They even placed the spacecraft into deep space hibernation to conserve energy - it woke up after 31 months when it passed close to the Sun and was charged by solar rays.

Chief scientist Matt Taylor said the analysis of the data from the surface, together with Earth-based observations, could provide our most detailed ever snapshot of a comet.

It is believed that comets which formed over four billion years ago could hold the key to how Earth was 'seeded' with water and organic matter, providing the building blocks for life.

Mr Taylor told Sky News: "This particular class of comet, Jupiter class comets, showed a similar flavour of water to what we see on Earth so possibly comets could have delivered the Earth's oceans, so water - and ultimately us, because we are made of water."