A European Space Agency probe has made a historic landing on a comet, but its status remains uncertain after harpoons failed to anchor it to the surface.
ESA officials said the lander, Philae, touched down on schedule Wednesday after a seven-hour descent from its orbiting mother ship, Rosetta. But during the free fall to the comet's surface, harpoons designed to anchor the probe failed to deploy.
Officials said the craft might have briefly lifted off after the initial landing on Comet 67P Churyumov-Gerasimenko before touching back down again.
The landing was the climax of a 10-year, 6 billion-kilometer journey from Earth. Rosetta had to slingshot three times around Earth and once around Mars before it could work up enough speed to reach the comet, which it did in August.
While the ESA still needs to ascertain the state of the 100-kilogram lander, the fact that it is resting on the surface of the comet already was a huge success. The agency hopes to know more about the state of the probe by Thursday.
Scientists hope that samples drilled out from the comet will unlock details about how the planets evolved. Comets date to the formation of the solar system 4.6 billion years ago. Scientists suspect impacting comets delivered water to the young Earth.
Rosetta and the Philae craft have cameras and nearly two dozen instruments to probe the comet's surface — and to analyze the material below it.
The box-shaped, 100-kg (220-pound) Philae landed on the comet around 16 hours Universal Time (11 a.m. EST) Wednesday, seven hours after separating from Rosetta.
The mission was considered risky because of the unknown surface of the comet and a problem with the thruster that was supposed to keep the probe from bouncing back into space.
Engineers designed the lander not knowing what type of terrain they would find on the comet's surface. Rosetta has been taking pictures of the comet and collecting samples from its atmosphere as it approaches the sun, showing it was not as smooth as initially hoped.
The team had to release the three-legged lander at exactly the right time and speed because there was no way of controlling it on its descent.
The touchdown is a first in space history. It is a proud moment for European space research and, as ESA Director General Jean-Jacques Dordain pointed out, for mankind.
"This is a big step for human civilization. ... This is certainly terrestrial intelligence," said Dordain.
After a period out of radio contact, mission control linked back up with both Rosetta and Philae as expected shortly after 1100 GMT, the ESA said.
Some information for this report was provided by Reuters. Lisa Bryant contributed from Paris.