Ceres is the largest object in the asteroid belt and the only dwarf planet in the inner Solar System. Although small, it has surprised us many times during the four years it's been investigated by NASA’s Dawn mission. One surprise was the discovery of ice volcanoes, technically known as cryovolcanoes, and researchers have now found evidence suggesting that the dwarf planet was volcanically active until recently. In fact, it might even be active today.
As reported in Nature Astronomy, researchers have discovered over 22 cryovolcanic domes on Ceres and used topography to work out the impact that these phenomena have had on the dwarf planet itself. The team estimates that throughout its history, Ceres' surface has been covered by roughly 10,000 cubic meters (353,000 cubic feet) of cryomagma – substances like water and methane that are expelled by cryovolcanoes – every year. A tiny volume, equivalent to roughly four Olympic-size swimming pools.
But while the amount erupted hasn’t added much, the fact that it was produced continuously is extremely important. Finding so many cryovolcanoes active over the last 4.5 billion years suggests that whatever powers such features is still there. And if Ceres can do it, other objects might be able to as well.
“Ceres is a little world that ought to be ‘dead,’ but these new results suggest it might not be," co-author Dr Hanna Sizemore, from the Planetary Science Institute in Arizona, said in a statement. "Seeing so much potential evidence for cryovolcanism on Ceres also lends more weight to discussions of cryovolcanic processes on larger icy moons in the outer solar system, where it’s likely more vigorous.”
The analysis is based on how cryovolcanos change over time on worlds like Ceres. Being made of a lot of ice, they tend to flatten over time, so the older mountains are much wider than they are tall. The youngest cryovolcano, Ahuna Mons, was identified as being just 200 million years old, so it has not had time to deform. The others, however, have slowly disappeared back into the surface over time. Unless they're at the poles.
"Ceres’ poles are cold enough that if you start with a mountain of ice, it doesn’t relax," lead author Michael Sori, from the University of Arizona, said in a statement. "But the equator is warm enough that a mountain of ice might relax over geological timescales."
The team found a mountain at a pole, matching the predictions, and used computer models to estimate the ages of the remaining cryovolcanos. It seems that one new cryovolcano pops up every 50 million years.
We don’t know the cause of cryovolcanos, but we might find some answers soon. The Dawn mission is nearing its end, but we have potentially spotted these geological features elsewhere, in the outer Solar System. It will be intriguing to see if Ceres is an exception to the rule.