Ceres's bright spots have been an enticing mystery ever since NASA's Dawn spacecraft began approaching the dwarf planet in the autumn of 2015. Now, research from the Max Planck Institute for Solar System Research (MPS) suggests the brightest of those shiny splotches — located within the enormous Occator crater in the northern hemisphere — is even more interesting than we thought. This region was probably a hotspot for cryovolcanic activity in the not-too-distant past.
After investigating infrared images of Ceres' surface taken by NASA's Dawn spacecraft, the team led by MPS' Andreas Nathues decided to take a closer look at the unusual bright material spread across Occator crater, and estimate its age. The distribution of this material, which appears to be carbonate salts, suggests that within this 92km-wide-long crater, icy brines — like lava but made of salt and water — once oozed to the surface in a process known as cryovolcanism. The crater itself was likely formed by a large impact.
"The age and appearance of the material surrounding the bright dome indicate that Cerealia Facula was formed by a recurring, eruptive process, which also hurled material into more outward regions of the central pit," Nathues, NASA Dawn's framing camera lead investigator, said in a press release. (Cerelia Facula is the name scientists have given to the bright spot in the Occator Crater's centre.)
"A single eruptive event is rather unlikely," Nathues added. His team's research has not been published yet.
By examining photos of Occator Crater, the team estimated the ages of bright material by looking at how strongly "perforated" each was — the less perforated the crater, younger it (probably) is. This is a pretty common method for ageing a surface. Ultimately, Natheus and his colleagues estimated that the bright carbonates in the centre of the crater are only about four million years old, meaning this area hasn't been inactive for that long — in cryovolcano time, of course.
It isn't the first evidence of icy volcanic activity on Ceres — in fact, for months, this has been one of the leading hypotheses for how so much shiny bright salty stuff came to be scattered across the dwarf planet's surface. There's also that weird, pimple-shaped mountain near Ceres' equator, which scientists suspect is a gigantic ice volcano — perhaps one of many. Taken together, all of this evidence suggests a surprisingly active world, with far more internal complexity than your average asteroid.
The only thing cooler than a volcano is an ice volcano, obviously. Scientists think they have spotted these mounds of icy rock — called cryovolcanoes — on many moons, such as Triton, Europa, Titan and demoted planet Pluto (sorry, Pluto). Perhaps the strangest one of all is Ahuna Mons, a solitary ice giant half the size of Mount Everest, located on the dwarf planet Ceres. But a new study suggests Ahuna Mons might not have always been the loneliest (ice) volcano in the solar system.
While there's still much we don't understand about Ceres, hopefully, a better understanding of its cryovolcanic activity will shed light on other icy moons in the solar system, too. Dawn continues to orbit Ceres and collect information on Occator Crater's reflective material, so this won't be the last we hear on the matter.