We found a match
Your institution may have rights to this item. Sign in to continue.
- Title
Replenishment of Near‐Surface Water Ice by Impacts Into Ceres' Volatile‐Rich Crust: Observations by Dawn's Gamma Ray and Neutron Detector.
- Authors
Prettyman, T. H.; Yamashita, N.; Landis, M. E.; Castillo‐Rogez, J. C.; Schörghofer, N.; Pieters, C. M.; Sizemore, H. G.; Hiesinger, H.; Marchi, S.; McSween, H. Y.; Park, R. S.; Toplis, M. J.; Raymond, C. A.; Russell, C. T.
- Abstract
Ceres' regolith contains water ice that has receded in response to insolation‐driven sublimation. Specially targeted, high spatial‐resolution measurements of hydrogen by Dawn's Gamma Ray and Neutron Detector (GRaND) reveal elevated hydrogen concentrations in and around Occator, a young, 90 km diameter, complex crater located at 19.82°N where near‐surface ice is not expected. The excess hydrogen can be explained by impact excavation of water‐rich outer crustal materials and their emplacement in the crater floor and ejecta blanket. This is supported by thermophysical models that show water ice could survive at sub‐meter depths, given Occator's relatively young age (∼20 Myr). We hypothesize that the regolith can be replenished with ice from large impacts and that this process partially controls the distribution and depth of near surface ice. This is supported by results from Occator and similarities in the global distribution of hydrogen and the pattern of large craters (20–100 km diameter). Plain Language Summary: The outermost meter of dwarf planet Ceres contains water ice that is gradually sublimating in response to heating of the surface by sunlight. Since Ceres' axis of rotation is nearly perpendicular to the Sun's rays, ice has receded to greater depths at the equator than the poles. The distribution of subsurface ice within this outer layer was inferred from measurements of hydrogen by Dawn's Gamma Ray and Neutron Detector. Special operations during Dawn's last mission phase brought the spacecraft close to the surface, enabling measurements within and around a large, young crater called Occator. Anomalously high concentrations of hydrogen were detected, suggesting the impact that formed Occator excavated water rich materials from the crust and deposited them on the surface. Comparison of the global distribution of hydrogen with the pattern of large craters on Ceres further supports excavation of crustal ice by impacts as a partial control on the depth of ice near the surface. Results confirm that Ceres' crust is rich in water ice and show that ice can survive in materials ejected by impacts into airless, icy bodies. Key Points: Neutron spectroscopy reveals enhanced hydrogen concentrations in the outermost meter of the surface of a prominent young, complex craterResults confirm Ceres outer crust is ice rich and support retention of water ice within impact ejecta on airless, icy bodiesThe data imply partial control of regolith ice content by large impacts, relaxing constraints on surface age and regolith grain size
- Subjects
GAMMA ray detectors; IMPACT craters; LUNAR craters; CERES (Dwarf planet); ICE prevention &; control; ICE; NEUTRON spectroscopy
- Publication
Geophysical Research Letters, 2021, Vol 48, Issue 15, p1
- ISSN
0094-8276
- Publication type
Article
- DOI
10.1029/2021GL094223