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Rosetta Comet-Chasing Probe Wakes Up
A comet-chasing spacecraft has beamed a signal back to Earth, ending nearly three years of hibernation.
The Rosetta probe is on one of the most technologically advanced missions ever attempted: to land on a comet at 24,600mph.
The spaceship was sent into a slumber in June 2011 so it could save energy for its long journey to the 2.5-mile frozen rock, known as 67P/Churyumov-Gerasimenko.
Rosetta's internal alarm clock gave the wake-up call at 10am GMT, but it took some eight hours for mission control to get confirmation it worked, scientists said.
"Hello, world!" the European Space Agency (ESA) said on Twitter, mimicking the signal sent back from deep space by the billion-dollar unmanned craft.
The agency described Rosetta as a "sleeping beauty" that had emerged from a long sleep.
"It was a fairy-tale ending to a tense chapter," the agency said.
Nerves were strained at mission control in Darmstadt, Germany, until the all-is-well message showed up as a spike in a radio wave, prompting cheers and backslapping.
"This was one alarm clock not to hit snooze on, and after a tense day we are absolutely delighted to have our spacecraft awake and back online," said Fred Jansen, ESA's Rosetta mission manager.
If all goes to plan, the probe will rendezvous with the comet in the coming months and drop its Philae lander docks onto its icy surface in November - a move that has never been attempted before.
The comet has almost no gravity, so the probe will have to use harpoons and ice anchors to clamp on to the surface.
Scientists have compared Rosetta's mission to a fly trying to land on a speeding bullet.
Comets are the primitive building blocks of the solar system, and are thought to have helped "seed" Earth with water, and perhaps even life.
Their icy surface is embedded with dust, grit and particles from space, Nasa says.
They are left over from a planet-building time when our Sun was just a spinning disc of dust and gas.
By studying the comet's dust and gas, it is hoped Rosetta will help scientists learn more about the evolution of the solar system.
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