Ceres’s Sunburn Dwarf Planet Ceres is a true enigma in our solar system. Ceres, the largest object in the asteroid belt, is distinct from almost all the other objects around it.
When our solar system formed, the inner part of the solar system was heated as the sun began to form, making it too hot for H2O-ice to condense in that area. The only materials that could condense to form solids are the things we find today in asteroids and in the rocky planets; solid silicates, oxides, and metals. In the outer part of the solar system, things were colder and ices could condense – but when ices condensed along with solids, gravity pulled in extra gas from the nebula forming the giant planets. That leaves Ceres as a true oddity. Ceres is an asteroid loaded with water and ice. In this shot of the bright spots at Occator crater, you see the remnants of water flowing up to the surface of the asteroid from the interior, depositing salts behind as it sublimates away. The surface minerals of Ceres contain carbonates like the mineral trona that are found in deserts on earth when water evaporates, clay minerals that form in the presence of water, and widespread outcrops of H2O-ice, particularly near the poles. So, where did Ceres’s ice come from? There are two possibilities. If Ceres formed where it currently sits in the solar system, then it must have formed after most of the heat from the forming sun ended. Ceres could have been made several million years after the formation of the solar system by combining H2O-rich objects into one large asteroid. How this process occurred isn’t well understood, but it can’t be ruled out. Alternatively, many scientists today believe that Ceres did not form in the asteroid belt, but instead it formed much farther out in the solar system. The Kuiper belt, out past the orbit of Neptune, is filled with objects like Ceres that contain huge amounts of H2O-ice. Sometime about a billion years after our solar system formed, the gravity of Jupiter and Saturn may have interacted in such a way to scatter the giant planets, causing their orbits to shift out away from the sun. If this occurred, then icy bodies out beyond Neptune could have been thrown throughout the solar system, potentially including Ceres. In this latter case, Ceres would have so much H2O-Ice because it is a sunburnt Kuiper Belt Object. The salts and clays at the surface would be leftovers, the residual solids after the icy layers sublimated away. Many of the salts and clays observed at the surface are the same ones observed in the outer solar system, including trona, which has been observed in the geysers of Enceladus. -JBB Image credit: https://solarsystem.nasa.gov/resources/619/occator-crater-on-ceres-simulated-view/ References: https://www.space.com/39992-dwarf-planet-ceres-water-active-surface.html https://doi.org/10.1016/j.icarus.2018.04.032 https://science.sciencemag.org/content/355/6320/55
