ESA Comet Landing

First Touchdown on 67P/C-G

Earth Receives First Images from Comet’s Surface
November 14, 2014

“Where we are now is gorgeous.”

After 10 years, four billion miles and a few big hops, the European Space Agency’s Philae lander transmitted photos and data from the surface of the comet, 67P/Churyomov-Gerasimenko, on the morning of November 13, 2014.

Welcome to Comet 67P/C-GThe first pictures from Philae (pronounced FEee-lay) form a panoramic view of its surroundings on the comet, and Philae’s scientists were more than a little shocked to find it right next to a large rock wall.

A bleary-eyed, Jean-Pierre Bibring presented Philae’s first data at a press conference at the European Space Agency’s Operations Center in Darmstadt, Germany Thursday morning of November 13. He confirmed Philae was in a more or less stable position on the comet’s surface and is currently very close to rocks and possibly even on a cliff side. At one point in his presentation, he referred to 67P/C-G as a “planet,” then quickly corrected himself confessing that giving presentations is difficult “when you go two nights without sleep.”

The reason Bibring and many other ESA scientists have not gotten any sleep is that Philae has had an extremely eventful landing, packed with both figurative and literal ups-and-downs.

Philae detaches from RosettaPhilae’s landing began at roughly 3:30 Wednesday morning – North Carolina time – of November 12 when Philae detached from Rosetta, the research satellite that carried Philae to the comet. Philae snapped a few pictures as it made its seven-hour descent to the surface of the comet.

Upon landing, ESA scientists had to wait 28 minutes – the time it takes light to travel from the comet to Earth – to learn whether Philae had reached its destination. But at 11:03 Wednesday morning – North Carolina time – NASA and ESA stations around the world received the signal. Philae had just become the first man-made object to make a soft landing on the surface of a comet.

After a brief celebration the ESA scientists at the control centers in Germany set to work analyzing Philae’s data and monitoring its progress.

Paolo Ferri, ESA’s Head of Mission Operations, said in a press conference Wednesday afternoon Philae “landed very close to the center of the error ellipse,” and ESA scientists confirmed Thursday morning Philae landed within 100 meters of their target.

In short: bullseye.

ESA also received a signal that coils on the lander’s harpoons were rewinding, indicating that the harpoons had fired and were holding Philae to the comet. They were also receiving information that Philae was continuously rotating, which it could not do if it was anchored to the comet.

Later on Wednesday, ESA found the harpoons had not launched for some reason and the reason Philae was spinning was that it bounced off the surface of the comet. Wednesday afternoon ESA’s Philae Lander Manager Stephan Ulamec announced Philae’s potential bounce joking, “Maybe we didn’t just land once, maybe we landed twice.”

Over Wednesday night, ESA scientists analyzed the data of Philae’s bumpy landing and Thursday morning, Ulamec not only confirmed Philae’s bounce, but also revised his joke as to the number of landings up to three.

“There is an inflation of landings,” Ulamec jested.

Philae made its first landing at the center of the red crosshairs in the picture, but may have bounced into the dark crater to the right in this picture. The researchers are currently using the Rosetta orbiter to find Philae’s exact position.

“We were very eager to get communication back this morning,” said Philae systems analyst Kuhn Gertz, who had been monitoring Philae’s travel until Rosetta made its expected dip below the comet’s horizon, making it impossible to communicate with Earth.

Comet 67P/C-G from 40 MetersThey were shocked to find such large rocks in Philae’s pictures because of the terrain inside the crosshairs, shown magnified in the picture. As of Friday morning of November 14, scientists were still searching for Philaes exact position.

ESA has a much better picture of how Philae is doing than where it is. Its cameras and batteries are working fine and Gertz said that scientific measurements are being conducted normally. All the news, however, is not as good.

Panoramic Lander OrientationThe lander may only have two of its three legs on the ground, with the third up in open space. While Philae currently appears to be stable, having only two legs on the ground prevents the harpoons from shooting into the surface and holding onto the comet.

Also, the change in location may prove problematic for Philae’s mission. The original landing site gets six to seven hours of sunlight per day, while Philae is only getting about an hour and a half of sunlight now. Since Philae is powered by solar panels, the lack of sunlight may jeopardize part of Philae’s mission to study to comet as it swings through the inner solar system next year.

Gertz said the onboard battery can keep Philae going for about 60 hours, and ESA scientists are scrambling to determine the long-term effects of Philae’s bounce.

“What we need to know is what this position means for us,” Gertz said.

While this position may not be ideal, Ulamec says that the lack of sunlight may not necessarily mean the end for Philae. The amount of sun the comet will get will dramatically change as it moves further into the solar system. Right now the comet is almost as far from the sun as Jupiter, but it will pass almost as close as Earth’s orbit, so while Philae is in the dark now, it may get more light later on.

Philae has an inactive mode, and a power saver mode and as of Friday morning, ESA scientists are making decisions about what should be done with the orbiter before the batteries die Friday afternoon. Ulamec says they will have one last shot at sending Philae commands before then.

For now, while Philae is still doing research, the scientists have to be extremely careful using Philae’s drills and mechanisms. The comet is small, about as wide as Manhattan Island, so the gravity there is very weak. Therefore, a wrong move could push Philae off the comet.

Jean-Pierre Bibring, however, said that capability might be an advantage. While it would be extremely tricky, there is a possibility that scientists could use those mechanisms to bounce Philae to a better spot on the comet, adding the caveat “if [we’re] clever enough.”

Regardless of any troubles Philae may be having, Bibring said Philae has already accomplished a great deal. He urged people around the world to focus on the images, the data, and the fact that Philae arrived at all instead of the current troubles.

“It’s amazing where we are,” said Bibring. “We landed. We analyzed a lot of things already in 20 hours. It’s amazing what we’ve been doing and what we will be doing by the end of this day. Please do not put emphaisis on the failures. Where we are is gorgeous.”

- Daniel Lane

Daniel Lane covers science, engineering, medicine and the environment in North Carolina.