Philae's Ulamec: Maybe We Didn't Land Just Once, But Twice

Philae's Ulamec: Maybe We Didn't Land Just Once, But Twice

Emphasizing that it is only speculation for now, the program manager for ESA’s Philae lander said today that the spacecraft may have bounced and landed not once, but twice on Comet 67P.  Stephan Ulamec and his team are still analyzing the data to determine exactly what happened, but the key message is that Philae did succeed in landing on the comet and returned scientific data and much more is expected.

Philae separated from its Rosetta mother spacecraft early this morning Eastern Standard Time (EST) and landed on Comet 67P/Churyumov-Gerasimenko just after 10:30 am EST.  Rosetta and Philae arrived in Comet 67P’s vicinity in August after a 10-year journey and scientists have been studying the comet’s surface in detail to determine the best landing spot to be used today. 

ESA has released many images of the comet taken by Rosetta as it orbits the comet, but scientists are anxious to see the view from the comet’s surface taken with Philae’s instruments. Today, ESA did not release any photographs of the comet taken by Philae after it landed, but did provide a photo from Philae when it was just 3 kilometers above the surface.   From that photograph, they determined that Philae was right on target to land in the center of the pre-determined landing ellipse. 

Image of Comet 67P from ROLIS camera on Philae lander approximately 3 kilometers above the surface. November 12, 2014. 
Credit:  ESA/Rosetta/Philae/ROLIS/DLR

ESA also released an image of Rosetta taken by Philae after the two spacecraft separated, and a photo of Philae, taken by Rosetta, as it descended to the comet’s surface.

Comets have almost no gravity, so Philae is equipped with harpoons to fire into the surface to hold it in place.  Minutes after it landed, Ulamec excitedly announced that Philae was on the comet and its harpoons had fired, but ESA soon tweeted a correction —  the harpoons had NOT fired.  It soon became clear that they were not entirely clear about Philae’s status other than that it was, indeed, on the comet’s surface.

At a later press briefing, Ulamec explained that not only is it “complicated” to land on a comet, but to understand what happened after landing. He and his team knew Philae had landed and received expected housekeeping and science data from many of the 10 instruments on the probe.  However, there were fluctuations in the radio link — it would cut out, but come back on immediately — and the solar generator.  They still do not know exactly what happened, but one possibility is that the lander bounced after its initial landing and then landed a second time. 

“Maybe today we didn’t just land once, we even landed twice,” Ulamec said excitedly, while emphasizing that it only speculation at this point to explain what they observed.

ESA has temporarily lost contact with Philae entirely now, but that was expected.  Philae communicates with Earth via Rosetta, so the link is lost when Rosetta moves below the horizon.  Paolo Ferri, head of Mission Operations for ESA, said they lost the link earlier than planned, but he said he is not concerned because the topography of the comet is not well known and a hill, for example, simply could be in the way.   Ulamec and Ferri conveyed confidence that communications will be restored tomorrow after Rosetta makes an already planned maneuver.

ESA Director General Jean-Jacques Dordain accentuated the positive — Philae landed, at the right place, and it has a radio link and electrical power so it can perform its tasks.  Beyond that, he pleaded for everyone to give the scientists time to analyze their data.

The next media briefing is scheduled for 14:00 Central European Time (CET) tomorrow, November 13 (13:00 UTC, 8:00 am EST).



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