The tiny robot lab may be ready to resume science work, adding a fresh chapter to its extraordinary voyage, excited officials said.
"Hello Earth! Can you hear me?" the washing machine-sized lander tweeted under the hashtag #WakeUpPhilae.
"We got a two-minute... successful communication" at 2228 Central European Time (2028 GMT) on Saturday, mission manager Patrick Martin told AFP from the operations centre in Madrid.
"This was sufficient to confirm that Philae is healthy and that its sub-systems are OK in terms of energy and temperature for ongoing communication with Rosetta," he said, referring to the lander's mothership orbiting Comet 67P/Churyumov-Gerasimenko.
The mission seeks to unlock the long-held secrets of comets -- primordial clusters of ice and dust that scientists believe may reveal how the Solar System was formed.
The 100-kilogram (220-pound) robot lab touched down on "67P" on November 12 after an epic 10-year trek piggybacking on Rosetta.
But instead of harpooning itself onto the dusty iceball's surface, Philae bounced several times before settling at an angle in a dark ditch.
It had enough stored battery power for about 60 hours of experiments, enabling it to send home reams of data before going into standby mode on November 15.
As "67P" drew closer to the Sun, scientists hoped better light would recharge Philae's batteries enough for it to reboot, then make contact, and ultimately carry out a new series of experiments.
After two failed bids to make contact in March and April, a new attempt was launched in May.
"We were surprised, yes, because we didn't expect it at all last night, on a weekend -- it's really exciting," Martin said.
An ESA statement said Philae communicated with its ground team for 85 seconds, and preliminary analysis of the data showed it must also have been awake earlier but unable to make contact.
According to Martin, the lander's temperature was about minus 36 degrees Celsius (-29 Fahrenheit) and its energy at 24 watts -- both higher than the minus 45 C and 19 watts required to operate.
"Philae is doing very well," said Stephan Ulamec, Philae project manager with the German space agency DLR. "The lander is ready for operations."
Martin was more cautious, saying: "We have already lined up more communication windows which hopefully will see a repeat of this successful communication.
"If we get a stable communications pattern we should be able within a week or so to think about operating the instruments on board the lander."
A tweet in the name of Rosetta announced: "Incredible news! My lander Philae is awake!", before prompting the robot to "take it easy for now" while checks are run to see that it is "fit, healthy and warm enough".
This prompted a Twitter response from Philae: "Oh, OK... I’m still a bit tired anyway... talk to you later!"
NASA tweeted "Rise and shine!" while Britain's usually staid Royal Observatory shouted: "YES!!!"
The comet and its precious cargo are 215 million kilometers (134 million miles) from the Sun and 305 million km from Earth, racing at a speed of 31.24 km a second, according to ESA's website.
Read more at Discovery News
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