The comet that the European Space Agency's Rosetta spacecraft has been chasing around the sun has a dark side. No, 67P isn't hiding any terrible secrets -- the southern hemisphere literally faces away from the sun during most of its 6.5-year-long solar orbit. Until recently, none of the cameras aboard Rosetta have been able to image it due to that utter lack of light, except for one -- the MIRO microwave instrument. NASA scientists behind the device have released a report on their observations, and lead author Mathieu Choukroun said "these unique data are telling us something very intriguing about the material just below its surface."
The MIRO instrument is designed to detect water both in comet 67P's "tail" and up to an inch below its surface. Early observations taken in June 2014, when Rosetta was still 350,000 km from the comet, showed that the highest concentration of water was in the comet's northern half. However, closer observations of the southern region taken with different wavelengths show that significant amounts of ice might lie within the first few inches of its surface, too. In fact, "it appears that either the surface material or the material that's a (few inches) below it is extremely transparent, and could consist mostly of water ice or carbon-dioxide ice," said Choukroun.
Despite problems with the Philae lander, Rosetta has given researchers a trove of valuable data about the comet, particularly its water composition. For instance, the amount of deuterium (heavy water) in 67P has strengthened the argument that Earth's water must have come from asteroids rather than comets. However, NASA said its odd water composition findings are still preliminary, and it plans to verify the results using data it collected more recently.