Just weeks before the European Space Agency’s Rosetta spacecraft makes the first observations of a comet at perihelion from the perspective of an orbiting spacecraft, researchers have gotten their first, long-awaited “taste” of Comet 67P/Churyumov-Gerasimenko … and does it reveal some surprises.
As Rosetta continues to orbit Comet 67P/Churyumov-Gerasimenko, early findings from its lander’s first set of scientific observations were published Thursday, July 31, in the journal Science. These findings encompass discoveries including, but not limited to, the composition of the comet, surface features and hardness, temperature, and magnetism. The space agency also released an image sequence underscoring what the lander saw as it descended to the comet’s surface. While Philae has been out of contact with the Rosetta orbiter since early July, it is hoped that these results aren’t the last pieces of information from the lander.
A Survey of Philae’s First Findings
A cometary surface “littered with coarse debris”: Long before Rosetta entered 67P/Churyumov-Gerasimenko’s orbit, it was believed the comet’s surface would be smooth; in addition, it was expected to have a uniform shape. These predictions were squashed when images beamed back to Earth during Rosetta’s approach revealed a double-lobed “duck shaped” world with a decidedly rugged surface. Philae’s cameras and instruments revealed even more about the comet’s features.
Philae famously bounced three times on Comet 67P’s surface before coming to rest at its final landing site, Abydos. Its initial landing site, Agilkia, was revealed to have “a surface coarse debris, pebbles and rocks with dimensions ranging from a few [centimeters] up to five [meters].” Abydos was shown to have similar terrain. ESA reported: “The images reveal fractures in the comet’s cliff walls that are ubiquitous at all scales. Importantly, the material surrounding Philae is dominated by dark agglomerates, perhaps comprising organic-rich grains. Brighter spots likely represent differences in mineral composition, and may even point to ice-rich materials.” Imagery from CIVA also confirmed Philae’s orientation upon its final resting place.
A multitude of organic compounds: Rosetta’s instruments COSAC and Ptolemy began to analyze Comet 67P’s gases and dust soon after its first landing on Agilkia. According to ESA, COSAC revealed “a suite of 16 organic compounds comprising numerous carbon and nitrogen-rich compounds, including four compounds – methyl isocyanate, acetone, propionaldehyde and acetamide – that have never before been detected in comets.” Ptolemy revealed “water [vapor], carbon monoxide and carbon dioxide, along with smaller amounts of carbon-bearing organic compounds, including formaldehyde.” DLR’s Stephan Ulamec, Philae lander manager, enthused, “Some of these are prebiotic molecules, which are important pieces that play a role in the emergence of life.” These findings may shed some light upon the origins of life in our Solar System, as comets are believed to be “relics” of its earliest days.
Hard soil possibly contributing to multiple landings: Philae’s MUPUS hammer probe showed that Comet 67P’s surface was much harder than previously expected, comparable to firn (granular snow). Once MUPUS penetrated a few centimeters of dust, it encountered “porous, yet solid” ice at Abydos. The comet’s hardness may have been a factor in why Philae bounced three times after failing to deploy its landing harpoons, and didn’t sink into the comet’s surface dust. This information about the hard surface may be useful in future cometary and even planetary missions. In addition, MUPUS’s temperature measurements showed variations of -180 to -145 degrees Celsius, confirming that Abydos indeed was a cold, dark landing site. According to ESA, Philae did complete 80 percent of its first science sequence last November. However, the lander “fell asleep” after 64 hours due to lack of power because of its location (until June of this year, of course).
Lack of a magnetic field: The Rosetta Lander Magnetometer and Plasma Monitor (ROMAP) showed during Philae’s descent that Comet 67P did not have a measurable magnetic field. DLR planetary scientist Ekkehard Kührt explained: “This confirms that, in the process of cometary formation from the solar nebula, the existing magnetic fields were not strong enough to align the individual dust particles magnetically and permanently magnetize the cometary material. Not a surprising but still an important finding for the development of formation models.”
Philae, which famously “woke up” in June, has been out of communication with the Rosetta orbiter since July 9. At present time, the Rosetta orbiter remains 170 to 190 kilometers from Comet 67P as the comet approaches perihelion, its closest point to the Sun. The spacecraft “stepped back” from the comet to preserve its safety, as 67P’s activity has increased in the last few weeks. The comet will reach perihelion on Aug. 13, giving researchers and Rosetta-watchers alike a thrill. At present time, Rosetta is observing Comet 67P’s Southern regions; the lander is at a Northern location, which may explain why it is having difficulty communicating with the orbiter.
Nicolas Altobelli, ESA’s acting Rosetta project scientist, is enthused about Philae’s initial results being returned on the eve of a major mission milestone: “These ground-truth observations at a couple of locations anchor the extensive remote measurements performed by Rosetta covering the whole comet from above over the last year. With perihelion fast approaching, we are busy monitoring the comet’s activity from a safe distance and looking for any changes in the surface features, and we hope that Philae will be able to send us complementary reports from its location on the surface.”
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