Rosetta Mission: dunes identified on Comet 67P
The collection of data of the Rosetta space mission by the European Space Agency, completed in September 2016 when the probe landed on Comet 67P/Churyumov-Gerasimenko, after 12 years of operations, is still ongoing. A team of French researchers from the Laboratoire de Physique et Mécanique des Milieux Hétérogènes has identified some dunes on the “lobes” of the comet’s surface. Their study was published in the Proceedings of the National Academy of Sciences (PNAS).
The images used by researchers were taken by the OSIRIS camera on board Rosetta, the main tool for the collection of images equipped with the WAC-Wide Angle Camera developed under the Italian leadership of Cesare Barbieri, University of Padua. Looking at the images taken by OSIRIS, French scientists saw that strong pressure difference between the sunlit side of the comet and that in shadow can generate winds able to transport dust grains and form dunes. They are found on both “lobes” of the comet and on the neck that connects them.
The comparison of two images of the same spot taken 16 months apart provides evidence that the dunes moved over time: this was unexpected finding since comets have a very rarefied atmosphere. According to researchers, the wind blowing along the comet's surface is caused by the pressure difference between the night side and the sunlit side, where the surface ice can sublimate due to the energy provided by the sunlight.
This study adds important information to the understanding of processes that regulate the phenomena found on comets’ surfaces to which scientists all over the world are currently working. In December 2016, the Science journal published a study conducted by an international team of researchers led by Gianrico Filacchione of the National Institute of Astrophysics (INAF) that, thanks to the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument – the spectrometer of the Italian Space Agency on board the Rosetta spacecraft – identified, for the first time ever, solid carbon dioxide on the surface of comet 67P, never seen before on any comet surfaces.