The dwarf planet Ceres is abuzz with geological activity. Researchers from Virginia Tech’s Department of Geosciences, along with members of the United States Geological Survey and the Planetary Science Institute, have now gained an understanding of what exactly is driving the body’s startling geological life.
Humanity didn’t get good views of Ceres’ surface until 2015, when NASA’s Dawn mission took the first (relatively) close images of the dwarf planet. With these came the revelation that the surface of Ceres is surprisingly diverse in terms of structures and composition. In turn, this indicated unexpected levels of geological activity brewing beneath the earth’s crust.
This came as a surprise to scientists around the world; Ceres, as its classification as a dwarf planet suggests, is very small. So small, in fact, that the researchers were absolutely convinced that it had completely cooled down to its core and was, geologically speaking, a dead world. What Dawn told us about the surface of Ceres revealed that it was anything but.
Tiny and fiery
Among the structures captured by Dawn were a large plateau on one side of Ceres (similar in size and nature to Earth’s continents), a localized series of fractures in its crust, and mineral deposits that hinted at an ancient ocean. evaporated. All of these structures could only have been created by geological activity fueled by immense amounts of internal heat.
Scott King, a geophysics professor in the geosciences department at Virginia Tech, wanted to figure out where that heat might be coming from.
On Earth, the heat that fuels geological and tectonic activity is inherited in small part from the time of the planet’s formation, with the rest generated by the decay of radioactive material beneath the crust. In this sense, the Earth acts a bit like a soft 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 modelling. Through such simulations, the team found that radioactive decay within Ceres could keep it hot enough to remain tectonically active.
Professor King explains that large planets, those the size of Earth or Mars, start out as very hot objects. All of this heat is produced by the myriad collisions between the particles that come together to create the planet – the friction involved in these collisions generates the heat. In the case of a smaller body like Ceres, there simply weren’t enough collisions to let it heat up the same way.
Thus, the models used by the team to simulate the internal heat of Ceres started from the baseline of a cold dwarf planet. They simulated various theories of how Ceres might have generated its heat using tools previously applied to study larger celestial bodies. The output of these simulations was compared to the data returned by the Dawn mission, to see which matched.
The model that best explained what the team saw on Ceres showed a unique sequence of events. The dwarf planet started out cold but warmed up due to the radioactive decay of elements such as uranium and thorium. This was enough to maintain its geological activity, but ultimately it pushed the internal structures of Ceres into upheaval.
This chain of events is supported by the presence of some of the surface features spotted by Dawn only on part of Ceres. The big plateau had no equivalent on the other side of the planet. Fracture systems were clustered in one place around this plateau and also had no equivalent on the other side of Ceres.
This concentration of features on just one side of the planet strongly suggests that there is a high degree of internal instability within the bowels of Ceres.
“What I would see in the model is that all of a sudden one part of the interior would start to heat up and move up and then the other part would move down,” says Prof King .
“It turned out that you could show in the model that where a hemisphere had this instability going up, it would cause extension at the surface, and that matched those fracture patterns.”
The model also suggests that Ceres did not follow the typical pattern of planets, starting hot and cooling, but instead went from cold to hot and then cold.
“What we’ve shown in this paper is that radiogenic heating alone is enough to create interesting geology,” says Professor King.
The results of this paper can help us better understand the geological activity of other dwarf planets and moons, the team believes. The moons of Uranus, for example, could be explored using a similar approach. They are similar in size to Ceres and NASA and the National Science Foundation recently considered them high priority targets for robotic missions – which can provide on-site data against which to validate our models.
The article “Ceres’ Broad-Scale Surface Geomorphology Largely Due To Asymmetric Internal Convection” was published in the review Advances AGU.