When NASA’s Dawn spacecraft arrived at Ceres it spotted several striking features, including Ahuna Mons, the largest mountain on the dwarf planet. It has a maximum height of about 5 kilometers (3.1 miles). Given that Ceres is less than 1,000 kilometers (620 miles) across, Ahuna Mons sticks out quite a bit. For scale, it would be like having a mountain 67 kilometers (42 miles) tall on Earth.
The peculiar formation emerged from smooth terrain and has bright streaks running from the top to the bottom of its slopes. There is no other mountain like it on Ceres and researchers believe it is the product of a curious geological phenomenon. As reported in Nature Geoscience, researchers think that Ahuna Mons was formed when a bubble of salt, water, and rock began pushing through the surface.
Using data from Dawn, scientists found evidence suggesting that the mantle underneath the dwarf planet’s crust is not solid and rigid. It is at least partially fluid and has convective motions within, powered by the heat of radioactive elements decaying. A plume of brine and mud extruding through the crust can explain the shape and composition of the mountain.
"We were thrilled to be able to find out which process occurring in Ceres' mantle, just beneath Ahuna Mons, was responsible for bringing material to the surface. Of course, Ahuna Mons was also a bit 'dubious' due to its shape as a volcano," lead author Ottaviano Ruesch, from the European Space Agency (ESA), said in a statement.
By tracking how the spacecraft orbited the dwarf planet, the researchers were able to create a map of its gravitational field. Beneath Ahuna Mons lies a gravitational anomaly. And this got the researchers excited.
"We took a closer look at this anomaly, and further modelling revealed that it had to be a bulge in Ceres' mantle," added Ruesch. "The conclusion was obvious: the mixture of fluid substances and rocks had come up to the surface and piled up into Ahuna Mons."
Ceres is the largest object in the asteroid belt and the only dwarf planet always within the orbit of Neptune. Ahuna Mons' name comes from the harvest festival of the Sumi Naga ethnic group in India.