August 3, 2014
Rosetta Records Temperature, Observes Coma As It Nears Comet 67P
redOrbit Staff & Wire Reports - Your Universe Online
After a journey of more than six billion kilometers through the Solar System, the ESA’s Rosetta probe is closing in on comet 67P/Churyumov–Gerasimenko (67P), and with less than a week to go until its arrival, it recently managed to take the comet’s temperature for the first time and has captured images of a coma surrounding its nucleus.
Rosetta, which lifted off from a European spaceport in French Guiana in March 2004, has already journeyed around the Sun five times, picking up speed through a series of gravity-assisted swingbys around Earth and Mars in order to achieve an orbit similar to 67P’s. Its goal, the agency said, is to match the 55,000 km/h pace of the comet and travel alongside it.
Since early May, the probe’s controllers have been running it through a series of planned maneuvers designed to reduce its speed with respect to the comet by approximately 2800 km/h in order to ensure it arrives by August 6. In the meantime, however, Rosetta has been able to use its instruments to conduct a series of observations and measurements of its target, allowing astronomers to learn more about the unusual, rubber-duck shaped comet.
Using its infrared and thermal imaging spectrometer (VIRTIS), Rosetta conducted a series of observations from between July 13 and July 21. Those observations, which came when the comet was roughly 555 km away from the Sun, revealed that the average surface temperature of 67P was approximately -70 degrees Celsius – up to 30 degrees warmer than predicted for an ice-covered comet at that distance, according to the ESA.
“This result is very interesting, since it gives us the first clues on the composition and physical properties of the comet's surface,” VIRTIS principal investigator Dr. Fabrizio Capaccioni said in a statement Friday.
He explained that the temperature measurements confirm most of the comet’s surface will be dusty, because darker material warms and emits heat more readily than ice when exposed to sunlight. The findings do not “exclude the presence of patches of relatively clean ice, however,” he added, “and very soon, VIRTIS will be able to start generating maps showing the temperature of individual features.”
In addition, images taken by Rosetta’s onboard scientific imaging system OSIRIS on July 25 clearly show signs of an extended coma surrounding the nucleus of 67P, according to NASA. The image covers an area of 150 by 150 square kilometers, said Luisa Lara from the Institute of Astrophysics in Andalusia, Spain, but scientists believe that it is actually much larger than that.
According to the ESA, OSIRIS previously detected a distinct rise in the comet’s activity which revealed a coma that spanned more than 1,000 km. While that activity ultimately died down, the new image confirms an extended coma close to the nucleus of 67P, where the particle densities are at their highest. They, too, predict that it extends much further into its surroundings.
Using the data collected by Rosetta on the satellite’s approach to the comet, the ESA said scientists have been able to learn more about how the comet behaves. Their analysis of this information will also allow them to determine whether or not there are “any localized spots of activity on the comet's surface,” as well as how this will correlate to the apparently asymmetric nature of the coma and other aspects of its overall development.
OSIRIS, VITRIS and the other instruments on Rosetta and its lander will “provide a thorough description of the surface physical properties and the gases in the comet's coma,” as well as keep track of changing conditions as the comet travels around the sun over the next year, said project scientist Matt Taylor.
“With only a few days until we arrive at just 100 km distance from the comet, we are excited to start analyzing this fascinating little world in more and more detail,” he added. The team has been conducting engine burns on a weekly basis throughout July in order to slow Rosetta down to prepare for its approach, and two short orbit insertion burns remain – one which will take place on August 3, and another which will occur on August 6.
Image 2 (below): OSIRIS wide angle camera view of 67P/C-G's coma on July 25, 2014. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA