Dwarf planet Ceres is a world of wonders. Organic materials are spread around its surface. There are ice volcanos and bright salt deposits. Now new research suggests that its pole may have wandered before settling into its current position, and this might be more evidence that it also once had an ancient subterranean ocean.
The new analysis, reported in Nature Geoscience, reveals the researchers found topographical irregularities on Ceres that are best explained by a polar shift. This polar wandering, or polar reorientation, happened due to a difference in the density of the crust. This led, over time, to a shift from its pole's original position, reorienting itself roughly 36 degrees to the current setup.
They determined this using three different sources from data collected by NASA’s Dawn mission. Ceres' crust sports many irregularities, including a slightly overdense equatorial region, which got researchers wondering "could these differences shift the dwarf planet's axis?" The team looked at other potential clues and found evidence of an ancient ridge. Equatorial ridges are seen in other icy bodies in the Solar System, the difference for Ceres, however, is that it is not where the modern equator is. Another very important piece of evidence is the presence of specific fractures indicating a shift in the tiny world's rotation, scattered on its surface.
“The most surprising aspect of this paper is to me the observation that the pole of Ceres must have followed an indirect path to its current pole," lead author Pasquale Tricarico, from the Planetary Science Institute, said in a statement. "A multi-step reorientation could mean that the equatorial density anomaly was still evolving during the reorientation, and this could be because the crust and mantle were weakly rotationally coupled, allowing the crust to start reorienting while the mantle would lag behind.”
This is exciting for the prospect of an ancient ocean below the surface. Researchers had already found evidence in the composition of the crust supporting the ancient ocean idea. This new study suggests that if it existed that could explain why the crust and mantle moved in different ways.
“If crust and mantle are allowed to shift with respect to one another, that could point to a layer of reduced friction between crust and mantle, and one of the possible mechanisms to reduce friction could be an ancient water ocean beneath the crust,” Tricarico added.
Dawn has spent three years studying Ceres and its many features. It is now in the final leg of its mission. It will continue to work until its hydrazine fuel runs out and then it will be placed in a stable orbit of the dwarf planet, to avoid contaminating its surface.