Extensive water ice within Ceres’ aqueously altered regolith: Evidence from nuclear spectroscopy

Abstract

The surface elemental composition of dwarf planet Ceres constrains its regolith ice content, aqueous alteration processes, and interior evolution. Using nuclear spectroscopy data acquired by NASA’s Dawn mission, we determined the concentrations of elemental hydrogen, iron, and potassium on Ceres. The data show that surface materials were processed by the action of water within the interior. The non-icy portion of Ceres’ carbon-bearing regolith contains similar amounts of hydrogen to those present in aqueously altered carbonaceous chondrites; however, the concentration of iron on Ceres is lower than in the aforementioned chondrites. This allows for the possibility that Ceres experienced modest ice-rock fractionation, resulting in differences between surface and bulk composition. At mid-to-high latitudes, the regolith contains high concentrations of hydrogen, consistent with broad expanses of water ice, confirming theoretical predictions that ice can survive for billions of years just beneath the surface.

A Global Inventory of Ice‐Related Morphological Features on Dwarf Planet Ceres: Implications for the Evolution and Current State of the Cryosphere

“…The FAE occur at a broad enough range of latitudes that lighting is unlikely to have biased their identification. The modest affinity of FAE to the southern hemisphere may be linked to the slight N/S asymmetry in near‐surface ice content inferred from GRaND data (Prettyman et al, ).…”

The Putative Cerean Exosphere

“…Up to nearly 10 4 computational molecules reside on the surface, the equivalent of about one week of supply. If outgassing rates are 0.003kg s −1 (Prettyman et al 2017), this amounts to up to 2 10 kg 3´o f water on the surface. Spread from the winter pole to a latitude of 83°( 10 10 m 2 ), its thickness is a monolayer.…”

“…Ceres has a crust rich in water ice (Prettyman et al 2017), and over time these molecules diffuse through the overlying porous layer, emerge on the surface, and continuously supply a water exosphere. Other chemical species could be occasionally delivered to the main belt (e.g., CO 2 ice from comet impacts) or percolate up from the interior (e.g., Ar-40 from decay of K-40).…”

“…Ceres, the largest body in the main asteroid belt, has abundant subsurface ice at a shallow depth (Prettyman et al 2017), and therefore it must have a tenuous water exosphere. Detection of an atmosphere on Ceres has been reported, but the occurrence is only episodic (A 'Hearn & Feldman 1992;Rousselot et al 2011;Küppers et al 2014;Roth et al 2016).…”

The Main Belt Comets and ice in the Solar System

“…Observations in the UV hinting at escaping water (A'Hearn and Feldman 1992) were confirmed in the sub-mm with detections with the Herschel space telescope ). Using nuclear spectroscopy data acquired by NASA's Dawn mission, Prettyman et al (2017) analysed the elemental abundances of hydrogen, iron, and potassium on Ceres. They found that the regolith, at mid-to-high latitudes, contains high concentrations of hydrogen, consistent with broad expanses of water ice.…”