Brine residues and organics in the Urvara basin on Ceres.

Abstract

Ceres is a partially differentiated dwarf planet, as confirmed by NASA's Dawn mission. The Urvara basin (diameter ~170 km) is its third-largest impact feature, enabling insights into the cerean crust. Urvara's geology and mineralogy suggest a potential brine layer at the crust-mantle transition. Here we report new findings that help in understanding the structure and composition of the cerean crust. These results were derived by using the highest-resolution Framing Camera images acquired by Dawn at Ceres. Unexpectedly, we found meter-scale concentrated exposures of bright material (salts) along the crater's upper central ridge, which originate from an enormous depth, possibly from a deep-seated brine or salt reservoir. An extended resurfacing modified the southern floor ~100 Myr after crater formation (~250 Myr), long after the dissipation of the impact-generated heat. In this resurfaced area, one floor scarp shows a granular flow pattern of bright material, showing spectra consistent with the presence of organic material, the first such finding on Ceres beyond the vast Ernutet area. Our results strengthen the hypothesis that Ceres is and has been a geologically active world even in recent epochs, with salts and organic-rich material playing a major role in its evolution.