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Using drills, Philae will dig up samples and analyze them with its on-board instruments.

Researchers hope to gain fascinating insights, because comets have remained largely unchanged since our solar system formed.

“This time capsule’s been locked away for 4.6 billion years,” said ESA director of science Mark McCaughrean.

One key question scientists hope to answer is whether comets are responsible for the water on Earth.

Rosetta and Philae will keep sending back data until their batteries die or the debris streaming off the comet irreparably damages their sensitive instruments.

Ferri said Philae’s useful lifetime could be as short as three days, while Rosetta is unlikely to survive beyond late 2016.

NASA, meanwhile, is also planning another space rock mission between 2019 and 2021. The agency is looking into sending a robotic spaceship to lasso a small asteroid and haul it close to the moon, where spacewalking astronauts would explore it.