Two articles, one published in the journal “Nature Astronomy” and one published in the journal “Science”, describe two studies about the comet 67P/Churyumov-Gerasimenko. The first is about a cliff Aswan in the Seth region of the comet’s nucleus that crumbled. The second article is about the changes that occurred on the comet’s surface detected thanks to ESA’s Rosetta space probe between the summer of 2014 and September 2016.
A team led by Maurizio Pajola of NASA/AMES and CISAS-University of Padua describes the events that started in September 2014, when a long fracture approximately 70 meters (70 feet) long and 1 meter (3’3″) wide was identified in the cliff called Aswan. On July 10, 2015, an amount of materials estimated at more than 27,000 cubic meters broke away from the cliff falling downwards. The Rosetta space probe’s Navigation Camera detected in that occasion violent jets of dust and gas as well but that was just the beginning.
After about five days, Rosetta looked back at Aswan discovering an edge much brighter than the dark surface where before there was a fracture. The collapse had left exposed an inner area of the comet 67P/Churyumov-Gerasimenko’s nucleus that was most likely composed of water ice. That brightness slowly faded suggesting that the ice sublimated over time. In observations conducted on August 6, 2016 that area was again very similar to those nearby.
A team led by Mohamed El-Ramy Maarry of the University of Boulder in Colorado, USA, summarized the types of changes observed over the course of about two years of the Rosetta space probe’s mission in orbit around the comet 67P/Churyumov-Gerasimenko. During its passage in the inner solar system, on its surface many changes occurred that were observed with an unprecedented continuity and accuracy. This provided researchers also a measure of the time taken by the various events that marked those two years.
The summary shows a number of different processes that emphasize the very intense geological activity during the comet 67P/Churyumov-Gerasimenko’s approach to the Sun. Many events are described and range from landslides to fractures on the surface but also boulders that move many meters and debris rains. The strong temperature variations caused erosion and ice sublimation even below the comet’s surface.
The heating of the comet 67P/Churyumov-Gerasimenko that occurred during its approach to the Sun also caused an acceleration in its rotation. One consequence was also a further stress on the nucleus which caused a fracture observed in August 2014 along the neck for a length of about 500 meters (1,600 feet) that in the following months got wider.
In June 2016 another fracture parallel to the first one was observed and because of the location in the area that connects the two lobes of the nucleus some questions have to be asked about the future of the comet 67P/Churyumov-Gerasimenko. If in the next few passages close to the Sun the fractures will keep on expanding and more of them will open it’s possible that in the future the comet might even break up.
The mission of the Rosetta space probe ended on September 30, 2016 with its impact on the comet 67P/Churyumov-Gerasimenko. Meanwhile, many studies have already been conducted thanks to the health of data it gathered and these two newly published ones provide a general idea of the considerable activity that there was over two years on the comet. It was really necessary to have a probe in the vicinity to get all those data, which allowed us to greatly expand our knowledge of comets.