The European Space Agency’s 1.4 billion-euros Rosetta mission on Wednesday achieved a first for humankind by successfully landing its Philae probe on comet 67P/Churyumov-Gerasimenko. Now, the lander’s fate hangs in the balance following a tense descent and the apparent failure of several key anchoring systems.
The ROLIS camera on Rosetta’s lander, Philae, took the above image of Comet 67P/C-G during the descent, only 3 km away from the surface. (Credits: ESA/Rosetta/Philae/ROLIS/DLR)
“We are extremely relieved to be safely on the surface of the comet, especially given the extra challenges that we faced with the health of the lander,” said Stephan Ulamec, Philae Lander Manager at the DLR German Aerospace Center, following news of the probe’s safe arrival at 11:03 a.m. EST.
“In the next hours we’ll learn exactly where and how we’ve landed, and we’ll start getting as much science as we can from the surface of this fascinating world,” he added.
Launched on March 2, 2004, Rosetta traveled 6.4 billion kilometers through the solar system before arriving at the comet on Aug. 6 of this year.
Philae’s Wednesday landing followed a seven-hour descent.
“This is the first body of this type that we’ve ever landed on,” James Oberg, a retired rocket scientist who is now an author and media consultant, told TechNewsWorld. “The last time we were on a comet, we hit it. This time, we got to kiss it.”
The 100kg lander was provided by a European consortium headed by DLR; other members of the consortium are ESA, CNES and institutes from Austria, Finland, France, Hungary, Ireland, Italy and the United Kingdom.
A Milligravity Atmosphere
Philae’s landing site was a spot named “Agilkia,” located on the head of the comet, a double-lobed body 510 million kilometers from Earth. The comet is littered with boulders; it has towering cliffs, daunting precipices and pits, and jets of gas and dust streaming from the surface.
Following the descent, which was made without propulsion or guidance, Philae actually may have landed not just once, but twice — apparently lifting off again briefly after the first time before resettling on the surface.
Gravity on the comet is so minimal as to warrant the term “milligravity,” Oberg said.
The consistency of the comet’s surface “is as weird as they feared,” he added, and thus “the failure of their grapple mechanisms looks serious.”
Signs of Trouble
Multiple pryotechnic charges don’t appear to have worked, and two harpoons failed to fire, Oberg said.
“Explosive bolts are standard equipment, but no one has ever exposed them for so long to such cold,” he explained. “There has been speculation in some of the space geek chat rooms that they could have a chemical issue.”
The most telling first indications of trouble were the “very dramatic and graphic hand movements” of the mission’s controllers as they “gathered in corners,” Oberg said. “They have not spoken in any detail, but the posture of their controllers speaks volumes.”
A ‘Fluffy’ Surface
With so little gravity on the comet, and with less anchoring than had been planned, it could be difficult for Philae to remain there as intended.
Moreover, “if the surface is as fluffy as it’s starting to look, some of the sampling mechanisms would have difficulty acquiring samples without throwing the probe,” Oberg explained.
Though Philae’s designers “clearly knew they’d be facing a challenge,” it remains to be seen whether the multiple mechanisms they included can cope with the reality of the conditions on 67P/Churyumov-Gerasimenko.
‘You Go Out There to Be Surprised’
“They’re looking at getting the situation stable and then relaying some pictures so they can figure out what the real status is,” Oberg said. “It’s going to be important to get some pictures from Rosetta of the landing site to see just how big a hole it made when it touched down — or maybe several holes.”
More details will surely emerge overnight, he added.
“As a spaceflight professional, my motto is, ‘boring is good,'” Oberg said. “As a human being, we want surprises. This is probably the only comet landing any of us will see in our lifetimes. You go out there to be surprised — if you didn’t want that, you’d stay home.”
An Onboard Laboratory
Assuming Philae can maintain its position, it will spend the next few days conducting its primary science mission. That includes capturing a full panoramic view of the landing site, including a section in 3D, as well as high-resolution images of the surface immediately underneath the lander. It will make an on-the-spot analysis of the composition of the comet’s surface materials, using a drill that will take samples from a depth of 23 cm and feed them to an on-board laboratory for analysis.
The lander also will measure the electrical and mechanical characteristics of the surface. In addition, low-frequency radio signals will be beamed between Philae and the orbiter through the nucleus to probe the internal structure.
An extended science phase using Philae’s rechargeable secondary battery may be possible if illumination conditions from the Sun permit and dust does not prevent it. This extended phase could last until March 2015. At that point, conditions inside the lander are expected to be too hot for it to continue operating.
Like Science Fiction
“This was a first, and all firsts are significant when it comes to complex space missions,” said Mario Livio, senior astrophysicist with the Space Telescope Science Institute.
“Furthermore, this mission almost resembles science fiction, and it is a wonderful feeling when science turns what was previously science fiction into an area of active research,” he told TechNewsWorld.
The detailed surface measurements that Philae makes at its landing site will complement and calibrate the extensive remote observations made by the Rosetta orbiter covering the whole comet.
“Comets are extremely important in giving us details about the history of the solar system,” Livio said.
Time for Renewed Commitment
Indeed, “we are effectively sampling materials in primitive, unaltered form that goes back to the origin of the solar system four and a half billion years ago,” noted William Newman, a professor in UCLA’s departments of earth, planetary and space sciences, physics and astronomy, and mathematics.
“This could shed a lot of light on our solar system’s origin,” he told TechNewsWorld, “and the role that cometary materials had in the subsequent evolution of our own planet as a result of their delivering to us carbon dioxide, water, and other materials that have helped to redefine our planet.”
China, India and Europe all have made “remarkable achievements” in planetary and space exploration over the past year, Newman said.
“Meanwhile, our space program seems to be frozen in time,” he lamented.
“There are many talented planetary and space scientists in this country who are unable to find in America suitable employment and the opportunity to develop missions that could alter our perspective of our place in the universe,” Newman observed.
“While our European colleagues deserve our kudos today,” he acknowledged, “it is time that we renew our commitment to space exploration — not to mention to potential economic benefits that could emerge — if this country is to return to its leadership role. We must not be satisfied with being No. 4.”