'Idle' comet probe 'a huge success'
The comet probe Philae managed to send back valuable data before effectively dropping in to stand-by mode when its batteries ran out of power, scientists have said.
Philae, which is the first spacecraft to land on a comet and study it, ran out of power early today as it lay in the shadow of a crater wall. Contact was lost at 0030 GMT.
The European Space Agency (ESA) had already managed to rotate the lander's body slightly in the hope that some light might hit its solar panels.
Lander manager Stephan Ulamec, who described the mission as "a huge success", said: "We still hope that at a later stage of the mission, perhaps when we are nearer to the Sun, that we might have enough solar illumination to wake up the lander and re-establish communication."
Now that Philae is in this "idle mode" with all its instruments and most systems having shut down, the ESA fears there could possibly be a long silence ahead.
Philae managed to return all of its housekeeping and science data, meaning that measurements planned for the final block of experiments on the surface were completed, the ESA said.
From now on, no contact will be possible unless enough sunlight falls on the solar panels to generate enough power to wake it up.
It took 10 years for Philae and its Rosetta mothership to reach comet 67P/Churyumov-Gerasimenko on Wednesday after an epic journey across four billion miles of space.
A tweet from the official Philae lander account before contact was lost said: "I'll tell you more about my new home, comet 67P soon... zzzzz."
High-resolution images from the orbiter are being studied in an effort to find Philae's final landing site.
Astrophysicist Elizabeth Pearson described the hope of making contact with Philae as "a long shot but it might happen".
She told BBC Breakfast: "The comet is rotating so every couple of hours Rosetta will be on the wrong side of the comet to Philae so it will lose the signal - that has been happening over the past couple of days.
"Now they are hoping that ,when Rosetta comes back in to signal range, Philae might have charged its solar panels enough to be able to charge back up and re-link up with Rosetta.
"Unfortunately where it actually landed means it gets a lot less sunshine a day - about an hour's sunshine in every 18 - which means it is not going to be able to charge as well as it hopes."
It needs about six hours a day to be maintained.
Scientists are still not sure of the probe's location after Wednesday's rollercoaster landing which saw the dishwasher-sized craft bounce twice before coming to rest more than half a mile from its original landing site.
Two harpoons which were supposed to anchor Philae to the ground failed to deploy, causing the probe to shoot 0.6 miles (1km) into space after its initial touchdown.
The comet is a 2.5-mile (4km) wide rugged lump of ice and dust, more than 300 million miles (483 million km) from Earth, strewn with deep pits, craters, cliff walls and jagged outcrops.
While scientists try to save Philae, attention will also turn to Rosetta, which now has to manoeuvre from its post-separation path back into orbit.
The Rosetta orbiter which is going around the comet is still going to be following the comet for another year or so as it goes around the Sun.
Rosetta is getting a global picture of the comet and is constantly monitoring every aspect. It has samplers on board and looking at what the comet's tail is made of.
The comet is currently travelling at about 40 times the speed of a bullet in an orbit around the sun.
Ms Pearson told BBC Breakfast: "Most of the core science from when it first landed has been uplinked to Rosetta. It is just a process of getting it all back to Earth and getting it back to the people who understand what is going on and going through it. It has actually been considered a huge success."
Scientists revealed they had managed to lift the lander's body about four centimetres and rotate it some 35 degrees in an attempt to capture more solar energy. But as the last science data fed back to Earth, Philae's power rapidly depleted.
Speaking from ESA's Space Operations Centre in Darmstadt, Germany, Dr Ulamec said: "It has been a huge success, the whole team is delighted.
"Despite the unplanned series of three touchdowns, all of our instruments could be operated and now it's time to see what we've got."
The story of Philae has been one of astounding human ingenuity and incredible good luck.
Merely to land on a comet has been hailed as one of the greatest scientific achievements of all time, and compared with aiming a fly at a speeding bullet.
But even before touchdown there were heart-stopping moments for the scientists. A computer glitch meant Philae had to be re-booted - effectively switched off and then on again - and then it proved impossible to activate the craft's downward thruster.
The active descent mechanism was meant to provide a downward force to help pin Philae to the ground. Not only was this not working, but on landing the probe's two spike-like harpoons failed to spring out and anchor it safely into the surface.
As a result Philae bounced not once but twice. The first bounce took it high over the comet, but there was never a risk of it vanishing into space. The comet's gravity is 100,000th that of the Earth, making the 100 kilogram lander weigh no more than a gram, but even that was enough to pull it back down.
It ended up a whole kilometre from the original landing site, scientists believe. Philae could have been dashed against one of the huge boulders that litter the comet's surface, or tumbled to oblivion, but instead it came to rest standing on at least two of its spidery legs inside a crater.
Scientists are still trying to pinpoint Philae's location and high-resolution images from Rosetti are being closely scrutinised.
Meanwhile the lander has returned unprecedented images of its surroundings. While descent images show the surface of the comet to be covered by dust and debris, the panoramic images also show layered walls of harder-looking material.
The science teams are now studying their data to see if they have sampled any of this material with Philae's drill.