The Water Regime of Ceres and its Potential Habitability
Abstract:Ceres is the largest object in the main asteroid belt of the Solar System, with a diameter of 940 km and accounting for ~1/3 of the total mass of the asteroid belt. The recent unequivocal discovery of water vapor associated with localized sources on Ceres by Herschel Space Telescope confirmed its enrichment in volatiles as suggested by its low density and previous observations and theoretical models. Hence water must have played a significant role in the evolution of Ceres and even affected its current state. Spectral reflectance of Ceres surface reveals the pervasive signature of hydrated minerals and carbonates. The albedo and spectral homogeneity suggest that processes involving liquid-phase activity at the global scale may have occurred in the past. The current evolution models of Ceres indicate that liquid water was present following an early differentiation and drove hydrothermal activity for a few tens of My since its formation. Silicate leaching could lead to the concentration of soluble species in an ocean that could play a role in lowering the freezing temperature of that layer. The likely accretion of low-eutectic species such as ammonia hydrates could have promoted the long-term preservation of a deep liquid layer at the base of an icy shell over extended periods of time (possibly until present).
The significance of water on Ceres and its active nature as revealed by Herschel observations not only suggest that Ceres is an object that potentially hides important clues about volatile history in the inner solar system, but also indicate a world of potential astrobiological interest. The Dawn spacecraft is scheduled to arrive at Ceres in March 2015 to perform detailed geological, spectroscopic, compositional, and gravity mapping. In the mean time, we have begun an observing campaign using ground- and space-based facilities covering wavelengths from UV to sub-mm, to fully characterize the nature of water and hydration features detected at Ceres, and to facilitate theoretical studies. We expect our knowledge of the history and current status of water on Ceres to be significantly advanced in the coming years.
Part of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.