Transient Mantle Convection on Ceres Answers Resurfacing Puzzle

Temperature cross sections showing radiogenic, heating-induced, convective asymmetry from a spherical convection model for results for Ceres, with four times indicated (400, 1200, 2400, 4000 Myr). Convective instability grows after 500 Myr and ceases after 2000 Myr. Credit: King et al., 2022.

At the time that the Dawn mission was proposed to explore the dwarf planets of the asteroid belt, it was assumed that these bodies had formed earlier than the larger planets and therefore served as time capsules recording an early solar system history that has been erased in the larger and more active terrestrial planets. However, when Dawn reached the largest body in the asteroid belt, the ice-rich dwarf planet Ceres, it revealed a puzzling youthful surface. A geologically young surface — with few ancient impact basins, large-scale fractures, and hemispheric crustal thickness variations — suggests an active and warm interior, which is challenging to explain given Ceres’ small size. This level of activity is commonly associated with icy satellites, where tidal heating serves as the dominant source of energy. Although Ceres is comparable in size to such satellites, it lacks tidal heating, leaving the energy source driving its internal activity unclear.

Scott King (Virginia Tech) led a team of researchers to investigate whether the heat generated by the decay of long-lived radionuclides (U, Th, K) is sufficient to allow the interior of Ceres to undergo convection (interior mantle motion), leading to young surfaces like those observed by Dawn. For Ceres, heat from radiogenic decay leads to transient asymmetric upwellings, where warm material ascends in one hemisphere and descends in the other. Initially, the interior is cold; however, as radionuclides decay, heat accumulates, and the interior can begin to convect. This convection occurs during the first 500-1,500 Myr of solar system history, after which radiogenic heating is insufficient to sustain additional activity. This transient convective instability can explain thickened crust, extensional fractures, and the absence of large impact basins. Transient asymmetric convection may also have occurred in other small solar system bodies, possibly explaining observed hemisphere-scale features on many satellites of Uranus and Saturn. READ MORE