The dwarf planet Ceres, tucked away in the asteroid belt between Mars and Jupiter, has been the subject of fascinated study by NASA's Dawn spacecraft. The current findings have shown that the planet is geologically 'alive' with ice volcanoes and small pools of water remaining from ancient oceans.
Data collected by the Dawn from 2017 to 2018, when the spaceship ran out of fuel, shows briny liquid seeping out on its surface, as well as mounds and hills that formed when ice melted and refroze after an asteroid impact about 20 million years ago. Though only a third of the width of our moon, Ceres' surface has become a subject of renewed fascination with astronomers.
These findings help add new information to the mysteries surrounding the Occator, a 57-mile-wide impact crater covered in bright salt deposits. Bulging mountains and hills also provide evidence that Ceres experiences a kind of ice-cold cryovolcanism, with briny mud or slush acting like molten lava does on Earth.
“We’ve provided strong evidence that Ceres is geologically active in the present, [or] at least in the very recent past,” says Dawn’s principal investigator Carol Raymond, the manager of the NASA Jet Propulsion Laboratory’s Small Bodies Program in Pasadena, California. “And there’s some tantalizing evidence that it could be ongoing.”
These new findings add Ceres to the growing list of worlds that had all the required ingredients for life at one point or another: liquid water, energy, and carbon-bearing organic molecules.
“We’ve got this recent, warm, wet geologic system that has all the ingredients that we think you need for life,” says Kirby Runyon, a planetary geologist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, who wasn’t involved with the studies.
Dawn's final missions had it flying within 22 miles of Ceres's surface and snapping high-resolution pictures of the salt deposits, which became one of the big mysteries of the Occator. The question was where the brines came from.
Researchers think Occator Crater is roughly 20 million years old. The impact that created it would have generated immense amounts of heat, turning the normally frigid landscape into a frothy bath of churning saltwater. But using computer simulations, the Dawn team found that the collision’s heat largely dissipated within five million years or so.
“If you were to drill, you might be able to reach an aquifer, and then you’d get very cold brine to come out,” says Bill McKinnon, a planetary scientist at Washington University in St. Louis who wasn’t involved in the new studies.
The teams studying this information concluded that the brine pockets that created these salt deposits are the remains of a massive ocean that might have once existed on Ceres. Dissolves salt keeps water in a liquid state, which keeps these water patches from freezing. The brines are estimated to be about minus 22°F, requiring a lot of salt and possibly a mixture of muddy, fine-grained minerals to stay in liquid form.
A team at Italy’s National Institute of Astrophysics found evidence that Occator’s bright spots include hydrated sodium chloride. The water component of this salt should boil off into space within a hundred years of coming to the surface, the researchers say. Since the material is still hydrated, though, Ceres’s icy volcanoes could still be chugging along.
“It’s very likely that this volcano is still active, in the sense that water, in a lower amount, is still rising,” says Dawn team member Andreas Nathues, a planetary scientist at Germany’s Max Planck Institute for Solar System Research and co-author of several of the new studies on Dawn's findings.