Sleep well, little Philae. (ESA)

After just over two days of working tirelessly, the Rosetta spacecraft's lander -- the indomitable Philae -- finally went to sleep.

The whole world cheered Philae's Wednesday landing, which marked humanity's first real landing of a probe on a comet. Comets are important to study -- because their ice probably contains the same molecules present at the start of the solar system -- and also difficult to land on, because of their speed. The comet that Philae landed on is traveling around the sun at about 84,000 miles per hour. Even though it's only about 300 million miles away, the probe traveled about 4 billion miles to reach it, slingshotting around the Earth three times to build up speed.

Tonight, Philae died as its mission control team watched from the ground.

The probe stopped working at 7:36pm Eastern Time -- just before it was schedule to lose touch with mission control anyway.

When Philae landed, it bounced off the ground several times instead of anchoring. While it initially hit right on its target landing spot, it ended up in a shadier area -- and its solar panels didn't get enough light.

Scientists decided to do as much research as possible with Philae's borrowed time, and even pulled a daring move to try to reposition the probe. Mission control ordered Philae to move its landing gear as a sort of arm, pushing it into a new position. It moved, but the battery was too close to dead for this repositioning to make a difference.

Philae sent back data until its final moments. In the coming hours and days, the Rosetta team will interpret this information to learn more about the comet. We may even know more later tonight.

"Prior to falling silent, the lander was able to transmit all science data gathered during the First Science Sequence," lander manager Stephan Ulamec said in a statement. "This machine performed magnificently under tough conditions, and we can be fully proud of the incredible scientific success Philae has delivered."

But we can still hope that Philae will make a come back.

Maybe the repositioning worked, and a few hours of sun will put Philae right again. Only time will tell. Because the comet's rotation keeps mission control from connecting to the probe for many hours at a time, there may be a delay between its successful recharge and our awareness of the fact. The next time we'll have a chance of getting in touch is 6am ET. ESA scientists say they'll be keeping an eye out for signs of life.

It's even possible that Philae will come back months from now to deliver new data. As the comet approaches the sun (with Rosetta still following its orbit and gathering info, which it will do for the next year) Philae's solar panels may receive enough light to power the probe on. This is a tricky business: At some point (probably around March) the sun will make the comet too warm for Philae to function at all. There's a careful balance between battery recharging and total destruction here, but maybe Philae will squeak by into that window.

After 10 years of hard work, the Rosetta mission made history by landing on the surface of a comet. The lander Philae touched down on the surface of a comet more than 300 million miles away. (European Space Agency)