Two new studies provide insights into the nature and origin of the dwarf planet Ceres, currently being studied by Nasa’s Dawnspacecraft. The studies, from Germany’s Max Planck Institute for Solar System Research and the Dawn science team respectively, concern the cause of bright spots on Ceres’ surface and the dwarf planet’s possible origins in the outer Solar System.
The 130 bright areas seen across Ceres have been the subject of great debate, and can finally be explained thanks to a team led by Andreas Nathues at the Max Planck Institute for Solar System Research in Göttingen. The study, published in Nature, concludes that “these unusual areas are consistent with hydrated magnesium sulfates mixed with dark background material”.
The magnesium salt in question, hexahydrite (MgSO4·6H2O), shares some chemical similarities with Epsom salt (MgSO4·7H2O), found on Earth. Based on images captured by Dawn’s framing camera, Nathues and his colleagues suggest that the bright, salt-rich areas are likely to have been created when water-ice sublimated in the past, due to asteroid strikes that exposed a mixture of ice and salt on Ceres’ surface.
The theory is further born out by haze clouds seen inside the pit of the crater Occtaor. The haze appears and disappears on a diurnal rhythm, which indicates that water ice is sublimating in the Sun’s heat.
AMMONIA SUGGESTS ORIGINS IN OUTER SOLAR SYSTEM
The same volume of Nature is home to a study by Nasa’s Dawn science team, which considers the implications of ammonia-rich clays detected on Ceres.
The composition of the material was identified through analysis of “data from the visible and infrared mapping spectrometer, a device that looks at how various wavelengths of light are reflected by the surface, allowing minerals to be identified”. Today, the dwarf planet’s relative warmth (180 to 240 degrees Kelvin or -93 to -33 degrees Celcius) would cause ammonia ice to evaporate, but ammonia molecules could remain stable in Dawn’s environment if they were bonded to other minerals.
According to Nasa, “the presence of ammoniated compounds raises the possibility that Ceres did not originate in the main asteroid belt between Mars and Jupiter, where it currently resides, but instead might have formed in the outer Solar System.”
Maria Cristina De Sanctis, lead author of the study, based at the National Institute of Astrophysics, Rome said “the presence of ammonia-bearing species suggests that Ceres is composed of material accreted in an environment where ammonia and nitrogen were abundant. Consequently, we think that this material originated in the outer cold solar system.”
Even if Ceres didn’t form at the outer edges of our Solar System, the materials that make it up almost certainly did.