Robotic probe awake for comet rendezvous and landingMonday 20 January 2014 20.18
The European Space Agency's comet chasing space probe, Rosetta, is awake.
The space craft sent a signal back to earth this evening for the first time in 31 months.
The signal was received by NASA's Goldstone ground station in California at 6.18pm, during the first window of opportunity the spacecraft had to communicate with Earth.
It was immediately confirmed in ESA's space operations centre in Darmstadt and the successful wake-up was announced via the @ESA_Rosetta twitter account, which tweeted: "Hello, world!".
It later tweeted: "Dia dhaoibh uilig ar domhan!"
The craft will now undergo essential health checks before continuing its journey to the comet 67P/Churyumov-Gerasimenko.
It is so far away that its radio transmissions, travelling at the speed of light, will take 45 minutes to reach listening stations in California and Australia.
The probe is presently located about 800 million km from Earth and just shy of Jupiter's orbit.
The spacecraft, which carries a 100kg lander called Philae, has been hibernating for most of the past three years to save power.
It is due to reach a 4km diameter comet called 67P/Churyumov-Gerasimenko in August.
Dia dhaoibh uilig ar domhan!— ESA Rosetta Mission (@ESA_Rosetta) January 20, 2014
The spacecraft is designed to put itself into orbit around 67P for more than a year of close-up studies.
Comets are believed to be the pristine leftover remains from the formation of the solar system some 4.6 billion years ago.
Scientists hope the mission will provide more clues about how the solar system came into existence.
One of Rosetta's first tasks will be to scout for a suitable landing location for its piggyback-riding Philae probe.
Scientists are particularly keen to conduct organic chemistry experiments on samples drilled out from inside the comet's body.
Engineers who designed the lander did not know what type of terrain they would find on the comet's surface.
It is outfitted with twin harpoons laced with tethers that will be fired into the comet's surface to anchor Philae and keep it from bouncing back into space after touchdown.
Europe spent about €1bn on the mission, which is due to run at least until the end of 2015.