Wake-up call for comet-chasing space probe Rosetta after long hibernation

Scientists at the European Space Agency were facing an agonising wait yesterday as they settled down to receive a signal from Europe's Rosetta probe, to confirm it has woken up from years of hibernation, before they can celebrate a new milestone in their unprecedented mission to land a spacecraft on a comet.

Dormant systems on the unmanned spacecraft were switched back in preparation for the final stage of its decade-long mission to rendezvous with comet 67P/Churyumov-Gerasimenko. They had been powered down in 2011 to conserve energy, leaving scientists in the dark about the probe's fate until now.

The earliest the agency might receive the probe's all-clear call was early morning Hong Kong time. If no signal is received, they will today try to manually restart the probe from the ground.

"We don't know the status of the spacecraft," said Paolo Ferri, head of mission operations at the agency. "There is a possibility that we're not going to hear anything. Two-and-a-half years are a long-time. We're talking about sophisticated electronics and mechanics. We've taken all possible precautions for this not to happen but ... problems may have happened."

While waiting for the first signal travelling the 800 million kilometres back to earth, scientists were holding a social media competition, asking space enthusiasts to compose and perform songs to "wake up Rosetta". The top entries are to be beamed to the spacecraft and the winner invited to witness the landing from the ESA's mission control room.

"There's apprehension and excitement. Some people have put their lives into this," said Matt Taylor, project scientist on Rosetta at the agency's Netherlands division. "But it's a bit like a teenager waking up. It takes some time to get out of bed."

Rosetta is named after a block of stone that allowed archaeologists to decipher ancient Egyptian hieroglyphs. Scientists hope the probe's findings will help them understand the composition of comets and thereby discover more about the origins and evolution of our solar system.

Comets are regarded as flying time capsules because they are essentially unchanged for 4.6 billion years. Scientists have speculated that comets - essentially giant, dirty snowballs - may be responsible for the water found on some planets. And like asteroids, comets also pose a theoretical threat to life on earth.