What Did We Learn From Landing On A Comet?

Philae is the first lander to touch down on a comet, but what have we learned since it landed?

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What did Philae learn in its first 57 hours on the comet? (The Christian Science Monitor)
"For 57 hours in mid November, a squat lander with spindly legs made history as the first spacecraft to visit the nucleus of a comet - sending a wealth of information on the object to solar-system scientists back on Earth."

Philae's battery is dead. But the mission was a huge success. (VOX)
"In terms of both scientific data and historical milestones, this mission was a huge success. In an extremely short time, the lander collected all sorts of information that will help us better understand the composition of comets."