EXPLORING NEW WORLDS WITH DAWN

To travel virtually into space to explore via a robotic emissary is a fascinating adventure. The Dawn spacecraft traveled deep into the main asteroid belt to unveil two new worlds, Vesta and Ceres. These bodies which comprise 45% of the total mass of the main belt are two endmember protoplanets from the earliest phase of solar system formation. The new views of these bodies exceeded expectations in nearly every measure and provided many memorable moments of surprise. Much was known about Vesta, since HEDs – meteorites presumed to have come from Vesta – have been pelting the Earth. While confirming Vesta as the parent body of the HEDs was a significant achievement, Vesta provided a wealth of new discoveries that reinforced the importance of geologic-scale exploration. Instead of one large impact basin, there were two overlapping basins, and defying expectations, no olivine was detected. Vesta’s geology was revealed to be complex, with giant trough systems and dark material mixing with the native bright material, often creating stunningly beautiful landscapes. Finally, the discovery of hydrogen on Vesta’s surface upended the long-held view that Vesta was entirely dry and rocky, and provided direct evidence of migration of volatiles within the early solar system. As Dawn approached Ceres, she beckoned with a blinding beacon. Dawn’s discoveries at Ceres were beyond imagination. This exotic and unique body displayed puzzling morphology and crater distribution, dotted with dazzling bright spots. Its surface was covered nearly homogeneously and unexpectedly in ammoniated clays, attesting to global aqueous alteration and an early subsurface ocean. Localized young deposits of concentrated sodium carbonate and salts indicated a chemically-evolved body similar to Enceladus. These deposits and Ahuna Mons, a singular recent cryovolcano, provide evidence for recent, possibly ongoing geologic activity. How many more fascinating new worlds await our probing?