Browsing by Author "Marchi, Simone"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
- Ceres' Broad-Scale Surface Geomorphology Largely Due To Asymmetric Internal ConvectionKing, Scott D.; Bland, Michael T.; Marchi, Simone; Raymond, Carol A.; Russell, Christopher T.; Scully, Jennifer E. C.; Sizemore, Hanna G. (American Geophysical Union, 2022-06)While we now know much about the volatile-rich world of Ceres from the Dawn mission, the deep interior remains something of an enigma, shrouded by a crust composed of water ice, carbonates, phyllosilicates, salts and clathrate hydrates. While smaller than most active moons or planets, Ceres has many features commonly associated with active, icy bodies including: hydrothermal, cryovolcanic, and tectonic features. Yet on active icy moons tidal heating is a significant component of the thermal budget; it is unclear whether radiogenic heating alone would be sufficient to supply the heat necessary for Ceres' interior to undergo solid-state convection. Here we show that transient asymmetric convection develops as the temperature within the body rises from heat generated by the decay of long-lived radionuclides (e.g., U, Th, K). The onset of transient asymmetric convection may reconcile a number of puzzling features on Ceres including: the missing large craters, Hanami Planum-the region of thickened crust, the gravity and crustal thickness, and the lithospheric stress state represented by the Samhain Catenae. Hemispheric-scale instabilities may also be important in the evolution of small bodies with small cores throughout the solar system, including the small icy moons of Saturn and Uranus as well as Kuiper belt objects.
- Composition and structure of the shallow subsurface of Ceres revealed by crater morphologyBland, Michael T.; Raymond, Carol A.; Schenk, Paul M.; Fu, Roger R.; Kneissl, Thomas; Pasckert, Jan Hendrik; Hiesinger, Harry; Preusker, Frank; Park, Ryan S.; Marchi, Simone; King, Scott D.; Castillo-Rogez, Julie C.; Russell, Christopher T. (Nature Publishing Group, 2016-07-01)Before NASA's Dawn mission, the dwarf planet Ceres was widely believed to contain a substantial ice-rich layer below its rocky surface. The existence of such a layer has significant implications for Ceres's formation, evolution, and astrobiological potential. Ceres is warmer than icy worlds in the outer Solar System and, if its shallow subsurface is ice-rich, large impact craters are expected to be erased by viscous flow on short geologic timescales. Here we use digital terrain models derived from Dawn Framing Camera images to show that most of Ceres's largest craters are several kilometres deep, and are therefore inconsistent with the existence of an ice-rich subsurface. We further show from numerical simulations that the absence of viscous relaxation over billion-year timescales implies a subsurface viscosity that is at least one thousand times greater than that of pure water ice. We conclude that Ceres's shallow subsurface is no more than 30% to 40% ice by volume, with a mixture of rock, salts and/or clathrates accounting for the other 60% to 70%. However, several anomalously shallow craters are consistent with limited viscous relaxation and may indicate spatial variations in subsurface ice content.