Ceres: 'Recent' ice volcano discovered on dwarf planet in asteroid belt

Photo: Ceres' mysterious mountain Ahuna Mons is seen in this mosaic of images from NASA's Dawn spacecraft. (Supplied: NASA)

Key points:

• Volcano likely less than 1 billion years old, much more recent than scientists thought possible
• Salty-mud volcano is half the height of Everest
• Scientists now say volcanoes may be more widespread than previously thought

 An isolated mountain discovered on the pock-marked dwarf planet Ceres has surprised scientists, who say it is a volcano that would have spewed freezing, salty mud.

Instead of molten rock, salty-mud volcanoes, or "cryovolcanoes", release frigid, salty water sometimes mixed with mud.

At 5 kilometres high, the mountain, dubbed Ahuna Mons, is about half the height of Everest — but the dwarf planet is just 1/13 the size of Earth.

Although the volcano is not active now, the research team was surprised that it appears geologically recent.

Scientists say Ahuna Mons looks like a volcanic dome. These form when thick molten material pierces the crust but does not explode or flow very far, instead squeezing up like toothpaste and building a bulge or dome on the surface.

"The Ahuna Mons cryovolcano allows us to see inside Ceres," said Dr Ruesch, a NASA scientist and lead author of a paper on this research released today in the journal Science.

"The same process might happen on other dwarf planets like Pluto."

Ceres' lonely mountain, Ahuna Mons, is seen in this simulated perspective view. The elevation has been exaggerated by a factor of two. The view was made using enhanced-color images from NASA's Dawn mission.

Young volcanism on an isolated dwarf planet is a surprise, as usually only planets, or satellites orbiting around them, have volcanoes.

Also, volcanic eruptions require bodies to be rocky, like Earth or Mars, or icy, like Saturn's moon Enceladus.

Ceres, in the asteroid belt between the orbits of Mars and Jupiter, is made of salts, muddy rocks and water ice: exotic and unexpected ingredients for volcanism.

Ahuna Mons formed 'within the last billion years'

Scientists now think volcanism might be more widespread than previously thought.

The mountain's appearance also indicates it is young on a geological timescale, Dr Ruesch said.

"We're confident that Ahuna Mons formed within the last billion years, and possibly within a few hundred million years," Dr Ruesch said.

This is relatively new geologically, given that our solar system is about 4.5 billion years old.

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.

However, Ahuna Mons is sharp, with fine features like the debris from rockfalls that should fade with time.

Also, older surfaces have a heavily pockmarked appearance from the accumulation of many impacts, but Ahuna Mons has few craters. 

"There is nothing quite like Ahuna Mons in the solar system," said Lucy McFadden of NASA Goddard, a co-author on the paper.

"It's the first cryovolcano we've seen that was produced by a brine and clay mix.

"Ceres, which orbits between Mars and the gas giant Jupiter, is interesting because it appears to be a transition object — it's not completely rocky, but it's not an ice world either."

The team plans to use the visible and infrared mapping spectrometer on NASA's Dawn spacecraft to determine the minerals that compose Ahuna Mons' surface