"Hello, world!" ESA said on Twitter, mimicking the signal sent back from deep space by the billion-dollar probe.
A webcast showed jubilant scientists at mission control in Darmstadt,
Its goal is to rendezvous in August with a comet, 67P/Churyumov-Gerasimenko, and in November send down a lander to carry out experiments on the icy wanderer.
The spacecraft, which carries a 100kg lander called Philae, has been hibernating for most of the past three years to save power.
Unlike previous comet probes,
Comets are believed to be the pristine leftover remains from the formation of the solar system about 4.6 billion years ago.
Scientists hope the mission will provide more clues about how the solar system came into existence, much like the Rosetta Stone, after which the spacecraft is named, provided a blueprint for deciphering ancient Egyptian hieroglyphs.
Scientists are especially keen to carry out organic chemistry experiments on samples drilled from the depths of the comet.
"It would be really interesting to find out whether the organic chemistry that is relevant for life is there on comets," Ulamec said.
Engineers who designed the lander did not know what type of terrain they would find on the comet's surface.
It is fitted with twin harpoons laced with tethers that will be fired into the comet's surface to anchor Philae. - Sapa-AFP-Reuters
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