Research teams working on the results of the European Space Agency's mission to comet 67P / Churyumov-Gerasimenko said that boulders are rolling on it and cracks are forming. It also turned out that the suddenly appeared and then faded bright spot is the inside of a comet filled with dry ice. How comet Churyumov - Gerasimenko has changed over two years of observations.
ESA / Rosetta
Close-up shot
The Rosetta probe with the Philae landing module was launched to comet 67P / Churyumov-Gerasimenko in 2004. Having entered the comet's orbit in 2014, the apparatus has been observing it for two years. In September 2016, it was decided to end the mission by making a hard landing of the Rosetta on a comet. This gave scientists the opportunity to take pictures of its surface at close range. According to preliminary estimates, Rosetta took the last photo from a height of 51 meters. However, after a more detailed examination of the data, ESA experts stated that only 20 meters remained to the surface.
Last photo taken by Rosetta © ESA / Rosetta
The data received by the station and the Philae lander are still being processed. Recently, international research groups published the actual results of two-year observations of the comet.
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Troubled surface
According to the images for different periods, scientists noticed changes in the relief: stones moved along the comet, landslides descended from the ledges, and the inner part of the comet opened slightly due to breaking off of surface fragments. So, a rather massive part of the Aswan cliff crumbled into fragments. A crack on it 70 meters long and about a meter wide was recorded in the fall of 2014. In July 2015, a few days after a cloud of dust and gas was noticed above the surface, part of the cliff was missing. But a bright spot appeared there.
ESA / Rosetta
"The last time we saw the crack was July 4th, and the absence of any other emissions over the next ten days is very strong evidence that that cloud is directly related to the collapse of the cliff," said Maurizio Pahola, who led the study of the comet at the Ames Research Center. …
As for the bright spot, this is the icy inner part of the comet. She, according to scientists, was able to reflect six times more light than the rest of the surface, which is why it seemed much brighter. By the end of December 2015, the stain faded. This suggests that most of the ice has evaporated. And by August 2016, this fragment leveled off with the rest of the surface, leaving only a small glimpse.
Probably, the processes occurring in the interior of the comet are behind the several breaks noticed. Approaching the Sun, the celestial body received more heat and light, while sharp temperature changes were noted on the comet. So, on the Aswan cliff, when exposed to sunlight, heating from -143 to +46 ° С occurred in 20 minutes. The impact of such drops on the ice contributed to the damage to the relief.
Non-lying stone
A study by another scientific group - from the University of Colorado - noted the changes that occurred to the comet after it approached the maximum distance to the Sun, and then began to move away from it. Such changes were, in particular, the cracks in the Anuket region. It is located at the narrowest part of the comet, the shape of which is often compared to a rubber duck. Previously, it was suggested that 67P was formed as a result of the collision of two celestial bodies, which is why it took on a strange shape.
In September 2014, scientists discovered that Anuket was cuts through a crack about 500 meters long. By December 2014, it increased by another 30 meters. Several cobblestones also moved near the crack. Pictures in the summer of 2016 showed that a second crack had formed near the first - from 150 to 300 meters in length.
Cracked comet © ESA / Rosetta
As the researchers note, this was due to the increase in rotation of the comet as it approached the Sun. According to Mohamed Rami el-Maarri, head of the research group at the University of Colorado, one day, as these cracks widen, a comet could split in two.
In the Khonsu region, researchers were able to track the movement of another, larger boulder. From May 2015 to February 2016, a block 30 meters wide and weighing about 13 tons moved 140 meters. The reasons for its movement are not fully understood, but scientists see two versions. The stone could be displaced under the direct influence of the release of the substance, which pushed it aside. Another assumption is related to the same process, but indirectly. The surface next to the boulder could gradually erode and sink, and it may have rolled back to a new position.
ESA / Rosetta
Nevertheless, the comet's distant past could have been much more active than its present: for two years, no particularly significant changes in the landscape could be noticed. This means that the Churyumov-Gerasimenko comet acquired most of its features long before the meeting with Rosetta. This is believed to have happened during its earlier revolutions around the Sun and probably in a different orbit.
Ekaterina Shutova