Dwarf planet Ceres powers its geologic activity using radioactive materials below its crust

Dwarf planet Ceres is abuzz with geologic activity. Researchers at Virginia Tech’s Department of Geosciences, together with members from the United States Geological Survey and the Planetary Science Institute have now inched in on what exactly drives the body’s surprising geological life.

Dwarf planet Ceres. Image credits NASA Goddard Space Flight Center / Flickr.

Humanity didn’t get any good views of the surface of Ceres until 2015, when NASA’s Dawn mission snapped the first (relatively) close-by images of the dwarf planet. With these, came the revelation that Ceres’ surface is surprisingly diverse in the matter of structures and composition. In turn, this pointed to unexpected levels of geologic activity brewing unseen below the crust.

This came as a surprise to scientists everywhere; Ceres, its classification of a dwarf planet suggests, is very small. So small, in fact, that researchers were absolutely convinced that it had cooled down completely all the way to its core and that it was, geologically speaking, a dead world. What Dawn was telling us of the surface of Ceres revealed that it was anything but that.

Tiny and Feisty

Among the structures, Dawn captured was a large plateau on one side of Ceres similar in size and nature to the continents of Earth, localized series of fractures in its curst, and mineral deposits that hinted at an ancient, evaporated ocean. All of these structures could only have been created through geological activity powered by immense quantities of internal heat.

Scott King, Professor of Geophysics at Virginia Tech’s Department of Geosciences wanted to understand where that heat could have come from.

On Earth, the heat that powers geologic and tectonic activity is in small part inherited from the days of the planet’s formation, with the rest being generated through the decay of radioactive matter under the crust. In this sense, the Earth acts much like a mellow nuclear reactor. The team decided to check if the same mechanisms could explain what we were seeing on Ceres.

The research relied heavily on computer modeling. Through such simulations, the team found that radioactive decay within Ceres could keep it hot enough to stay tectonically active.

Prof. King explains that big planets, those the size of Earth or Mars, start out as very hot objects. All this heat is produced by the myriad collisions between the particles that are drawn together to create the planet — the friction involved in these collisions generated the heat. In the case of a smaller body like Ceres, there simply weren’t enough collisions happening to let it warm up the same way.

As such, the models the team used to simulate Ceres’ internal heat started from this baseline of a cold dwarf planet. They simulated various theories as to how Ceres could have generated its heat using tools previously applied to study larger celestial body. The output of these simulations was checked against data returned by the Dawn mission, to see which fit.

The model that best explained what the team was seeing on Ceres showed a unique sequence of events. The dwarf planet started out cold but heated up due to the radioactive decay of elements such as uranium and thorium. This was enough to maintain its geologic activity, but eventually it drove the inner structures of Ceres towards upheaval.

This chain of events is supported by the presence of some of the surface features spotted by Dawn only on one part of Ceres. The large plateau did not have a counterpart on the other side of the planet. Fracture systems were clustered in a single location around this plateau and similarly did not have a counterpart on the other face of Ceres.

This concentration of features on a single side of the planet strongly suggests that there is a high degree of internal instability in the bowels of Ceres.

“What I would see in the model is, all of a sudden, one part of the interior would start heating up and would be moving upward and then the other part would be moving downward,” Prof. King explains.

“It turned out that you could show in the model that where one hemisphere had this instability that was rising up, it would cause extension at the surface, and it was consistent with these patterns of fractures.”

The model also suggests that Ceres didn’t follow the typical pattern planets go through, starting out hot and cooling down, but instead went from cold to hot to cold again.

“What we’ve shown in this paper is that radiogenic heating all on its own is enough to create interesting geology,” Prof King explains.

The results of this paper can help us better understand the geologic activity of other dwarf planets and moons, the team believes. The moons of Urus, for example, could be explored using a similar approach. They are similar in size to Ceres and NASA and the National Science Foundation recently deemed them high-priority targets for robotic missions — which can supply on-site data against which to validate our models.

The paper “Ceres’ Broad-Scale Surface Geomorphology Largely Due To Asymmetric Internal Convection” has been published in the journal AGU Advances.

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