The Comet 67P Churyumov-Gerasimenko has a particular double-lobed shape, and its ‘dark side’ was a complete mystery until the recent discovery made by the Rosetta Spacecraft, according to NASA.

The 67P comet was discovered in 1969 by two astronomers from Ukraine: Klim Churyumov and Svetlana Gerasimenko. NASA reported in a press release that several photos and data from around the south pole of the comet, the darker and colder region, were taken after five and a half years that the zone remained inaccessible. Added to its mentioned shape, the inclination of the comet’s axis explains the seasonal pattern that the comet repeats on its six-year long orbit.

Not every comet in space shows and spheric shape. Some comets are irregular, due to the lack of gravity that should make them have an determined configuration. Copyright: ESA/Rosetta/NAVCAM, CC BY-SA IGO 3.0

According to scientists, the seasons take place for different amounts of time on both hemispheres, one being considerably longer than the other. The northern hemisphere suffers a long five-year summer, as the southern pole experiences a heavy winter. But as the comet reaches his point closer to the sun, the situation reverts, transiting the weather to a hot summer on the south pole.

“At the beginning of the southern summer, we had a paucity of observations in these regions as Rosetta’s trajectory focused on the northern hemisphere due to ongoing communication with the lander, Philae. However, closer to perihelion we were able to begin observing the south”, said Matt Taylor, ESA Rosetta project scientist.

The Rosetta spacecraft, a project of the European Space Agency, reached the 67P comet in August 2014, during the long summer happening on its northern pole. For five years, southern regions were immersed in a total blackout night, making data recording highly difficult. The Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) couldn’t be used by Rosetta to register the pictures, due to the lighting conditions. But there was one instrument that did work: the Microwave Instrument for Rosetta Orbiter (MIRO).

Researchers pointed out the very-likely presence of ice below this southern regions: “surprisingly, the thermal and electrical properties around the comet’s south pole are quite different than what is found elsewhere on the nucleus,” added Choukroun. Primarily, the nucleus of a common comet is composed by rock, dust, and frozen gases. When those gases are expelled due to the heating of the comet, the classic ‘tale’ is produced. 

“We observed the ‘dark side’ of the comet with MIRO on many occasions after Rosetta’s arrival at 67P/C-G, and these unique data are telling us something very intriguing about the material just below its surface,” said Mathieu Choukroun from NASA’s Jet Propulsion Laboratory (JPL) lead author of the study, according to the NASA press release.

Although the results are based on primary research, scientists say that water and gases released by the comet when it is closer to the sun can explain the difference between the surface and subsurface composition showed by the data. The water cycle –evaporating, condensing and precipitating– took place after the season went back to its regular winter. However, scientists insist on the relevance of taking more exact data from the polar region.

Choukroun said that they will review the MIRO data, updating the model, so they can take a second look at the results to verify them and give them new interpretation hypothesis. Also, the scientists count with the Rosetta’s lander Philo, although they experienced some communication trouble mentioned by Matt Taylor before.

“We hope that, by combining data from all these instruments, we will be able to confirm whether or not the south pole had a different composition and whether or not it is changing seasonally,” concluded Mark Hofstadter, the MIRO principal investigator.

What is Rosetta doing?

The Rosetta mission launched on March, 2004. On its early stages, the mission provided long-distance pictures of several comets and asteroids, as well captured information from the atmospheres of Mars and Venus.

Now, the spacecraft backed up some miles –about 930 (1,500 kilometers)– so they can have a wider look of the comet’s environment. After spending some time doing that, its attention will be on both poles, taking as much data as it can to make proper comparisons.

Source: Jet Propulsion Laboratory, NASA