Science News reports that dwarf planet (and largest asteroid) Ceres has multiple ice volcanoes, as opposed to just one, like scientists have thought since 2015. NASA's Dawn spacecraft, which was launched in 2007 specifically to study Ceres and the asteroid belt's other largest object, Vesta, found one ice volcano when it first approached Ceres in 2015, and scientists dubbed the feature Ahuna Mons. They were surprised to find only one such feature, but recent images show that the others were there; they were just hiding.
Ahuna Mons reaches about 3 miles above the dwarf planet's surface, and it is much greater in diameter than in height, so similar features should have been easy to find from satellite imagery, but that wasn't the case. In the interest of making sure they hadn't missed any, scientists at the University of Arizona in Tuscon theorized that the surface of the dwarf planet might be erasing older ice volcanoes over time, so they came up with a computer simulation to simulate the life cycle of a Cerean ice volcano.
The simulation indicated that over millions of years, the conical shapes of ice volcanoes relax and spread out due to a process known as viscous relaxation. Imagine a viscous substance like honey or crude oil. When you pour it out, it maintains a bit of a three-dimensional structure, but as the substance's own weight bears down on the structure, it tends to spread out into a more stable, pooled shape. Because the material in an ice volcano is liquid-based and viscous, the computer models showed that over millions of years, the weight of Ceres's ice volcanoes causes them to spread out evenly into a flatter shape.
Using the measurements gained from the computer simulation, the ASU scientists searched the Dawn data from Ceres again. This time, they found 21 more ice volcanoes, almost all of them spread flat. One was not, though; Yamor Mons, according to Phys.org, was wider and flatter than Ahuna Mons, but still taller than the other ancient volcanoes on the world. It was also located at a pole, where the average temperatures are much colder than on the rest of the dwarf planet.
All of these observations led scientists to determine that Ahuna Mons was not the largest or only cryovolcano on the planet, it was just the newest, at less than 200 million years old, so it had not had time to fully disperse yet, like the others had. Yamor Mons is older than Ahuna Mons, but retains much of its shape because its structure is protected by the extreme cold of the pole.
Astronomers theorize that cryovolcanoes on Ceres have a tendency to ooze more than explode violently, like Earth's magma volcanoes do, and that they eject only a fraction of the material thrown out by Earth volcanoes. Scientists look forward to comparing what they've learned on Ceres to other cryovolcanic bodies, like moons Europa and Enceladus.