Philae landed 3 times on comet, but scientists not sure where it is

The Philae probe is alive and well a day after the first successful spacecraft landing on a comet, but scientists are still trying to figure out exactly where it is on its new home.

Officials at the European Space Agency mission control in Darmstadt, Germany, confirmed Thursday that the lander, launched from the Rosetta spacecraft circling comet 67P/Churyumov-Gerasimenko, is busily sending data back to Earth -- including the first images ever taken from the surface of a comet.

These early images show a haunting terrain covered in dust and debris that range in size from a few millimeters to several feet. One image taken at the orbiter’s first landing site showed what looked like a square block about 15 feet wide.

While it was touching down, the lander bounced twice -- almost as if the comet were a trampoline. The first bounce lasted almost two hours and took the lander about two-thirds of a mile above the comet’s surface. The second bounce was smaller and lasted just a few minutes, said Stephan Ulamec, the Philae landing manager. The craft’s harpoons failed to attach it to the surface after touchdown Wednesday but it’s now stable, scientists said.

“We know how we landed, but we don’t know where,” Ulamec said. “We landed three times.”

The lander then settled in a shadowy part of the comet near a cliff, where it is only getting 1 1/2 hours of sunlight a day. At its planned landing site, Philae would have gotten six or seven hours of sunlight. The difference is crucial because Philae will need to rely on solar power after its batteries run out after about 60 hours, and this will affect how much work the probe can do on the surface, mission officials said.

Scientists also said Philae landed with two legs on the ground and one foot in the vaccuum of space during its final touchdown. Ulamec said the lander has the capability to make a little “hop” on the surface, which could help it get into a better position, but the maneuver would be risky and it is not likely ESA will try it.

And because Philae’s harpoons failed to keep it tethered to the comet, ESA officials are also wary of drilling into the comet as planned. Their concern is that the force of the drills on such a low-gravity body could cause the lander to move again.

The ESA team conceived the risky Rosetta mission in the late 1980s to learn more about comets that formed from the same mix of gas, dust and other ingredients that would form the sun, Earth and other planets. Spacecraft have slammed into comets before, but none had ever landed intact before Wednesday.

Although there were some hiccups with the landing, the science and engineering team at ESA said that was to be expected. They knew virtually nothing about the topography and gravity of the comet when they launched the mission 10 years ago.

“If we had known the comet, we may have thought of a different design for the orbiter,” said Ulamec. “Still, we put a lot of thought of possible scenarios and possible surfaces, and even after what we know of the comet now, I don’t think we would have designed it that differently.”

“What is really impressive is not the degree of failure we encountered, but the degree of success we’ve had,” said Jean-Pierre Bibring, Philae’s lead scientist and a principal investigator on two of its instruments. “It is amazing where we are. We landed on a comet. We are really at the limit of what humankind could do now -- it is gorgeous where we are.”

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