Since March 2015, the Dawn spacecraft has been orbiting the dwarf planet Ceres, in the main asteroid belt, which is located between Mars and Jupiter.
With a diameter of 950 km, Ceres is the largest body of the area but it had never been explored before the visit of Dawn. The probe revealed a much more complex than imagined world that probably contains ice in its subsoil and in some areas of the surface as well as organic molecules.
New observations indicate that the appearance of the surface of Ceres evolves as a function of its distance from the Sun. This is the first time such an observation has been made concerning this dwarf planet.
These observations are focused on the Juling crater, which is located on the southern hemisphere of Ceres. It is approximately 20 km in diameter and 1.5 km deep. They were carried out between April and October 2016 and show an increase in the amount of ice lining the north wall of the crater which is mostly in the shade. During this period, the dwarf planet in its astral race approached the Sun, which triggered a release of water vapor from the subsoil, which then condenses on the cold walls of the crater, explains Andrea Raponi of the Institute of Astrophysics and Planetary Science in Rome, in a study published in the journal Science Advances.
This type of sublimation-condensation phenomenon is common on comets but unexpected on Ceres. It is also possible that some of the ice exposed was due to small landslides that exposed sections of the subsoil.
The Dawn spacecraft has also obtained new images of the highest mountain of Ceres, Ahuna Mons which culminates at four kilometers of altitude. It is one of the few sites on the dwarf planet where a significant amount of sodium carbonate hydrate was found, represented in green and red in the image at the bottom right. It is this element which forms the mysterious luminous spots present in several craters and in particular Occator. The presence in large quantities of this hydrated element at several sites also suggests recent modifications of the surface. Indeed, like the ice that sublimates, the carbonate dehydrates (in a few million years) and is therefore of recent appearance, geologically.