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The European Space Agency's Philae lander touched down on a comet more than 300 million miles from Earth on Wednesday, completing its 10-year journey.
The historic landing, scientists hope, will provide them with insights on the origins of our solar system. Comet 67P/Churyumov-Gerasimenko, which circles the Sun every 6.5 years, is made of ice and rock that scientists believe dates back to the time when the planets were forming.
It wasn't all smooth sailing. As the probe landed, readings indicated that its cold-gas thruster system didn't fire properly, according to officials at the DLR German Aerospace Center Ulamec. Harpoons meant to secure the lander on the comet did not engage.
The result? It bounced twice, but now, according to officials, it's "safely on the surface of Comet 67P/Churyumov-Gerasimenko."
That's one small tweet for man, one giant tweet for mankind
Seeing as unmanned landers can't exactly utter famous lines, the Philae lander's Twitter account has been speaking for it. Some of its tweets have been spectacular.
After landing, it posted a partial selfie on the comet's rocky surface.
The European Space Agency (ESA) even created a GIF of the lander descending towards Churyumov-Gerasimenko from the Rosetta spacecraft, which has been trailing the comet since August.
As expected, Rosetta lost sight of Philae for a little while as it disappeared below the comet's horizon.
What happens now?
Philae will spend the day taking thermal measurements of the soil, ESA officials said at press conference on Thursday morning. The plan is for Philae to eventually deploy its drill, take samples of the comet, analyze them and send those results to Rosetta, which will then relay them to Earth.
Stephan Ulamec, the Philae lander project manager, said that he is hesitant to deploy the drill until he knows exactly how Philae is sitting on the comet's surface. If deployed while the lander is not properly anchored, it could tip Philae over, he said.
Meanwhile, scientists eagerly await data from the lander.
“One early result that we are now waiting for is the measurements on the analysis of the debris cloud that was kicked up by the landing," Stan Cowley, a planetary scientist at the University of Leicester who was involved in the early stages of the mission, said in a release.
“One key result concerns the oxygen isotope ratios in the comet water — are they the same as at Earth and the Sun, or different?"
Philae will also be capturing images and sounds from the comet. On Thursday, Rosetta sent back the first panoramic photograph from Churyumov-Gerasimenko. That was a couple days after the ESA released audio of the comet "singing" — or, more accurately, the "oscillations in the magnetic field in the comet’s environment."
It's not clear how long the Philae lander will be able to carry out its mission. It's currently receiving "very little power from the solar generator," ESA officials said, meaning that it's relying on its current store of battery power. That should allow it to operate for around 60 hours.
The hope is that the lander can deploy its drill before running out of juice. Even if Philae's battery dies now, it could be revived in several months if its position receives more sun. Regardless, Rosetta should continue orbiting the comet for at least another year.