Update, 13 November: 5 p.m. CET/11 a.m. ET
The Thursday afternoon press briefing confirmed what we've been learning all day: Philae is between a rock and a hard place. More specifically, it's on its side, one leg sticking up in the air—and in the shadows of a looming crater wall a few meters away. Solar panels are receiving only about 1.5 hours of light a day, when the goal was for 6 or 7 hours per day to recharge the lander's batteries. Drilling into the subsurface would have to wait until the very end of Philae's 60 hours of battery life—for fear that it could upset the lander. Yet mission leaders were largely upbeat about being alive and doing science. Most of the lander's 10 instruments were taking data, and engineers were exploring options to use the spring of the lander legs or other ground-poking instruments to jostle the lander into a more favorable position. "Do not focus on the failure of the system," implored Philae lead scientist Jean-Pierre Bibring, who showed a panorama of six CIVA images and its unsettling portrait of the lander's position. "It's gorgeous where we are."
How did Philae get to this spot? Philae project manager Stephan Ulamec explained how, after impact on Wednesday, the lander rebounded at 38 centimeters per second, traveling a kilometer up in space, and a kilometer laterally across the surface. The lander bounced again, a little bit. The strong rebounds are an indication that beneath the soft, fluffy dust at the surface lies something tougher. "This material is like a trampoline," Bibring says. Radar data helped locate an approximate position for its final resting spot—somewhere just within the rim of the large crater on the head of the duck-shaped comet, what was once known as landing site "B." Holger Sierks, principal investigator for the orbiter's camera, was waiting for images to be downloaded to Earth tonight that he thought would contain the lander. By comparing before-and-after pictures—by hand—and looking for a 3x3 pixel dark patch, he hopes to locate Philae. "We'll find the lander," he said.
So it's looking like Philae is in a tough spot. But engineers have many creative ways both to hoard energy and extricate their robots form precarious positions—so I would not be suprised if this is just the beginning of Philae's time on 67P/Churyumov-Gerasimenko. Even if the 1.5 hours of sunlight is not enough to recharge Philae's batteries warm, the mission could, in theory, come out of hibernation later on with seasonal improvements in sunlight.
Update, 13 November: 12:45 p.m. CET / 6:45 a.m. ET
CIVA, the panorama camera on Philae, has released its first picture, and it shows the lander in a distressing position. A lander leg is visible, but it's hard to tell which way is up. There is no view of the sky—or perhaps it's that blackness at left—and there's lots of shadow. The darkness is particularly worrisome. Philae will need sunlight in order to recharge its batteries. It has just over 50 hours of juice left right now. "The big fear is cold," says Gerhard Schwehm, the former mission manager who retired less than 2 years ago. He said it looked like the lander was on its side, or maybe in a ditch—but at least the head of the lander was pointing up. This was known for sure because of the good radio connection. The next day will be of assessing the present environment to see how much science can be done in such a compromised position. Two instruments, APXS and MUPUS, have not been deployed for fear of upsetting the lander, and, at the moment, drilling is out of the question. At some point, with dwindling batteries, action could be taken—even though Philae is a comet lander, and not a comet hopper. A decision could be made to try and fire the unactivated harpoons—even at the risk of launching the lander into space. Another possibility could be using the penetrator on the MUPUS instrument—a hollow rod 35 centimeters long that could be pressed into the soil. But first the team must make heads or tails of where they are before they start to consider, erm, last-ditch improvisations.
Update, 13 November: 10 a.m. CET / 4 a.m. ET
I'm back at ESA's operation center for a second day, following Philae's harrowing, but ultimately successful landing on the surface of comet 67P/Churyumov-Gerasimenko. This morning, Philae project manager Stephan Ulamec told me something improbable: Philae bounced, in a really big way. He says that, after impact, the lander may have flown as high as 1 kilometer back into space (this is microgravity, after all) before returning again to the comet. It may have bounced a second time a little bit before finally coming to rest. The good news: Mission managers now have steady radio contact with Philae, and science data are being gathered. We expect to see panorama pictures from the CIVA camera, maybe even before a planned 2 p.m. CET media briefing. The bad news: Philae remains unanchored by its harpoons. That might make managers less willing to operate the drill, which could jeopardize the lander's stability.
Many of the TV crews have already packed up and left, and the press room is virtually empty. But today is the day that we really begin to learn about Philae's new home.
Update, 12 November: 6:03 p.m. CET/12:03 p.m. ET
Ferri also says he is confident Philae landed near the center of the landing ellipse -- maybe within 100 meters.
— Eric Hand (@erichand) November 12, 2014
Paolo Ferri says the lander is safe but may not be completely stable.
— Eric Hand (@erichand) November 12, 2014
Update, 12 November: 5:11 p.m. CET/11:11 a.m. ET
Success! Philae has landed on a comet. Philae project manager Fred Jansen confirmed the touchdown. "We are sitting on the surface, Philae is talking to us, more data to come."
We have yet to hear of the condition of the lander—much remains unknown about its health, or how benign the environment is: whether it is sitting flat and happy. Assuming the lander is healthy, it will begin a first run of preprogrammed science, lasting about 7 hours. First will be CIVA, taking panoramas to understand where Philae landed within Agilkia. Then come instruments such as the gas-sniffing Ptolemy and COSAC. The lander has enough batteries to last on its own about 3 days. After that, it will require recharging from its solar panels—and could survive until March 2015.
We may expect to receive first images from Philae later tonight.
Update, 12 November: 4 p.m. CET/10 a.m. ET
And we have now seen the most stunning image of the mission so far. Holger Sierks—who has been criticized for being stingy in releasing images from his OSIRIS camera—just unveiled a jaw-dropper: the spidery, three-legged lander floating down against the black background of space. These images surely belong in a pantheon of sorts, along with the Mars Reconnaissance Orbiter's snapshots of Curiosity and Phoenix parachuting down to the Red Planet. There is always something poignant about one robot taking a picture of another robot, unimaginably separated from the human beings that created them.
Update, 12 November: 3:40 p.m. CET/9:40 a.m. ET
After several glimpses on control room screens, we finally have seen proof of Philae's separation from Rosetta: the CIVA camera's "farewell snap." The image shows Rosetta's solar panels amid the glare and glint of sunlight. We are now in the phase of the landing descent where dignitaries are making speeches. But touchdown is rapidly approaching—still on track for an hour window centered on 5 p.m. CET/11 a.m. ET.
Update, 12 November: 2:15 p.m. CET/8:15 a.m. ET
Yesterday, I had the chance to meet Klim Churyumov, who discovered Rosetta’s cometary target in 1969, along with Svetlana Gerasimenko. Through a translator, the 77-year-old astronomer at Kiev State University in Ukraine recalled the special expedition he made 45 years ago to a 0.5-meter telescope in the mountains near Almaty, the capital of Kazakhstan. “The whole world knows about this comet,” he says. “At the beginning, we didn’t know anything. We didn’t have such a nice shape. It was just a bright dot.” The astronomers kept taking images, and noticed some smudging on their photographic plates—a sign of 67P’s atmosphere, or coma. “It was clear that it was not a star,” Churyumov says. Asked how he was feeling about the prospects of landing on his namesake, Churyumov said that he was excited. “For me, it will be a moment of truth,” he says. “It’s an inspiration. We’ll jump.” For more on the discovery of 67P/Churyumov-Gerasimenko, see this nice ESA-produced piece.
Update, 12 November: 12:12 p.m. CET/6:12 a.m. ET
After a tense wait, relief spreads through the control room as ESA reestablishes contact with both Rosetta and Philae, which are now talking to each other. Mission control managers can now watch Philae through its slow, unpowered descent.
Update, 12 November: 10:30 a.m. CET/4:30 a.m. ET
Where is Philae going? This is a picture of Agilkia, the 1-kilometer-wide circle that is the target area for the lander. Most of that uncertainty comes from errors in the velocity at which Philae was shoved off of Rosetta; the remainder comes from errors in the known position of Rosetta's orbit. You can see that the landing zone is by no means completely flat and smooth. There are boulders and sheer slopes that could upset the lander. On Monday, Philae project manager Stephan Ulamec told me that 20% of this landing terrain is pitched at angles greater than 30°, slopes that could pose a problem. Add in the threat of boulders, and most mission managers are talking about a probability of success of about 75%. But no one really knows. The problem with the gas thrusters—which are supposed to press the lander to the surface while its harpoons and footpads fix themselves to the ground—cannot help. Decades of work are going to come down to a crapshoot.
Update, 12 November: 10:13 a.m. CET/4:13 a.m. ET
The 7-hour descent to the comet surface has begun. Applause burst out in the ESA control room upon receiving confirmation that Philae had indeed separated from the Rosetta spacecraft. "It's on its path down to the comet," says flight director Andrea Accomazzo. Stephan Ulamec, the Philae project manager, said he was feeling "released, or relieved." "The lander is on its own now," he says. It will be a long wait in the meantime. We are hoping that we will get a farewell image of Rosetta taken by CIVA, the lander's panoramic camera, at about the halfway mark, around 2 p.m. CET.
Update, 12 November: 8:10 a.m. CET/2:10 a.m. ET
The predelivery burn was a success! And the landing sequence is going ahead. Rosetta's release of Philae comes in less than 2 hours. But there is a problem: The cold nitrogen gas thrusters that were supposed to press the lander against the surface appear not to be working. Philae will have to rely on its other two tools needed to stick the landing. It still has two harpoons and spinning screws in the tips of each of the lander's three feet. The harpoons are to puncture harder, icy materials, and the screws are to burrow into the surface if it is softer. But part of the point of the thrusters was to prevent any rebound that might occur because of the harpoons. Couldn't the landing be attempted again in 2 weeks' time? Project manager Fred Jansen says that they made two separate attempts to measure a rise in pressure in the gas tanks that would have signaled them being ready to fire. Making that measurement again in 2 weeks' time wouldn't make any difference, he says.
Update, 12 November: 7 a.m. CET/1 a.m. ET
Good morning! There are some bleary eyes here in the European Space Agency's control room in Darmstadt, Germany. But that is surely outweighed by the momentous activities that await. First up: We're expecting to learn soon about a 6-minute-long "predelivery burn" on the Rosetta spacecraft. This would put the orbiter in a position to drop the Philae lander in a few hours. This terrific video explains the orbital mechanics of what's about to happen much better. (The burn in question happens at the 47-second mark.)
DARMSTADT, GERMANY—On Wednesday, 12 November, the Rosetta spacecraft's Philae probe is set to attempt an historic landing on a comet, known as 67P/Churyumov-Gerasimenko. In a technological tour de force, the probe will slowly approach the comet, then attempt to touch down and use harpoons to secure itself to the surface. A suite of onboard instruments will be taking scientific measurements.
ScienceInsider's Eric Hand is at Rosetta mission control in Germany, following the action, and will be updating this blog with the latest news, starting at 1 a.m. Wednesday morning U.S. Eastern Standard Time. Please join us.
Rosetta officials are scheduled to make a "go/no-go" decision on the landing attempt at about 2:35 a.m. Wednesday (U.S. EST). If it's "go," the lander will separate from Rosetta at 4:03 a.m. and start sending images of the landing at 10:01 a.m. Touchdown is expected at 11:02 a.m. But the terrain is diffcult, and success is not assured.
The European Space Agency will be webcasting the event: http://rosetta.esa.int/
NASA TV online will be covering Rosetta starting at 9 a.m.: http://www.nasa.gov/multimedia/nasatv/index.html
To read more Rosetta coverage, visit our Rosetta collection page.