The dwarf planet Ceres hosts an unexpectedly young cryovolcano, analysis of images from NASA's Dawn mission has revealed. Instead of molten rock, salty-mud volcanoes, or “cryovolcanoes", release frigid, salty water sometimes mixed with mud. The cryovolcanic formation on Ceres is named Ahuna Mons.
“Ahuna Mons is evidence of an unusual type of volcanism, involving salty water and mud, at work on Ceres," said study lead author Ottaviano Ruesch of NASA's Goddard Space Flight Center, Greenbelt, Maryland, and the Universities Space Research Association in Washington, DC. “Geologic activity was discussed and debated among scientists: now we finally have observations testifying to its occurrence," Ruesch noted.
Although the volcano is not active now, the team was surprised that it appears geologically recent. Young volcanism on an isolated dwarf planet is a surprise, as usually only planets, or satellites orbiting around them, have volcanism. Also, volcanic eruptions require bodies to be rocky, like Earth or Mars, or icy, like Saturn's moon Enceladus. Ceres is made of salts, muddy rocks and water ice: exotic and unexpected ingredients for volcanism.
Ahuna Mons on Ceres indicates such physical and chemical limitations to volcanism are only apparent. As a consequence, volcanism might be more widespread than previously thought. “The Ahuna Mons cryovolcano allows us to see inside Ceres," Ruesch said. “The same process might happen on other dwarf planets like Pluto," Ruesch noted.
The team used images and 3-D terrain maps from the Dawn mission to analyse the shape of Ahuna Mons. They compared features and models of known mountain-building processes on Earth and Mars to the features found on Ahuna Mons. According to the research, published in the journal Science, it is the combination of features that makes the case for a volcanic dome. For example, the summit of Ahuna Mons has cracks like those seen in volcanic domes when they expand.
Also, the slopes have lines that resemble those formed by rockfalls, and the steep flanks surrounding the dome could be formed by piles of debris. The mountain's appearance also indicates it is young on a geological timescale. Surface features on planets with little or no atmosphere like Ceres get eroded by asteroid and meteoroid impacts, and take on a soft, rounded appearance. “We're confident that Ahuna Mons formed within the last billion years, and possibly within a few hundred million years," Ruesch said.
This is relatively new geologically, given that our solar system is about 4.5 billion years old. “Ahuna Mons is telling us that Ceres still had enough heat to produce a relatively recent cryovolcano," Ruesch said. “There is nothing quite like Ahuna Mons in the solar system," said co-author on the paper Lucy McFadden of NASA Goddard Space Flight Center. “It's the first cryovolcano we've seen that was produced by a brine and clay mix," McFadden noted.