JOIN USComet probe eludes scientists
The probe landed off-kilter on November 12, 2014. Knowing where Philae now lies is crucial to understand whether enough sunlight will reach its solar panels to recharge and awaken the dormant lander. The angle of sunlight will change in the coming months as the comet approaches the Sun.
Where is it?
Jean-Pierre Bibring, a planetary scientist at the Institut d’Astrophysique Spatiale in Orsay, France, and chief scientist for the lander, is confident that Philae will awaken early this year, perhaps sometime between February and April. But he conceded that estimate relied on exactly where the lander is. “The only question is the site,” he said at a meeting of the American Geophysical Union in San Francisco.
A series of high-resolution images being downloaded this week from the orbiting Rosetta spacecraft may finally be able to pinpoint Philae’s location. “I find it a bit strange that four weeks after landing, we don’t have it,” says Holger Sierks, a planetary scientist at the Max Planck Institute for Solar System Research in Göttingen, Germany, and chief scientist for the camera on Rosetta that is searching for Philae.
That camera, called OSIRIS, looked for Philae on Nov. 24 and again on Dec. 6. It combed an area measuring 350 meters by 50 metres on the lip of a crater rim where Philae is thought to have come to a stop. The Dec. 6 scan turned up an
intriguing glint outside the search area that could have been a reflection from the spacecraft, Sierks says. But the entire region was in shadow at the time, so it is difficult to say what the camera was actually seeing.Location is crucial
OSIRIS tried again on December 12, 13 and 14, looking at a larger area that
includes both the original scan site and the intriguing glint. The data are being downloaded now and could be available in as early as a day or two.
Because sunlight illuminated the area during the most recent search, the team is hopeful that it will see something. “It’s a bit like waiting for Christmas
presents,” says Matt Taylor, Rosetta project scientist at the European Space Agency.
Philae needs the order of 15 watts of power to awaken and be able to perform science. Its location on the comet, and the angle at which its solar panels are oriented to the Sun, will determine how long it might take to gather that power.
Bibring says that the lander is currently receiving only about four and a half hours of sunlight a day.
Environmental matters
Philae’s survival also depends on whether it can withstand the frigid temperatures on Comet 67P. Its instruments are rated to 65 degrees Celsius below zero and can probably survive conditions a bit colder than that, says Bibring. “We are confident we are in an environment to survive until the energy on the solar panels is back to what we need.”
In February, Rosetta will descend to within 10 kilometers of the surface and perform its closest comet fly-by ever. After that, the Sun’s heat will cause so much gas and dust to fly off the comet that it will be too dangerous for Rosetta to approach. The mission’s goal is to study how the comet’s activity changes as it gets closer to the Sun.
Comet 67P will swing past the Sun in August 2015. The Rosetta mission had been scheduled to end in December 2015, but ESA is considering extending it for several months beyond that, Taylor says.