Occator Crater on the dwarf planet Ceres gained much attention during the days of the Dawn mission at the small world when bright spots were imaged within the crater. Back in 2015, images were released by the spacecraft’s team that showed these bright spots, and the media coverage went a little wild. There were even some internet comments about the possibility of alien cities, but then, aren’t there always comments about how it’s aliens.

Note: It’s never aliens. Until it is aliens. But I digress.

Over time and much to the dismay of everyone with a vivid imagination, the bright spots in Occator turned out to be brine-related salts or possibly ammonia-rich clays. In 2016, the consensus was that the spots are made of sodium carbonate and indicated some form of subsurface hydrothermal activity. Wait. Hydrothermal activity? Ceres could be another world with a subsurface ocean? Yes. Yes, it could be. And in 2020, NASA confirmed just that, reporting that there is a deep reservoir of brine that percolated to the surface in the crater and other various locations, causing the various bright spots.

Today, in a brand new paper published in Geophysical Research Letters with Planetary Science Institute senior scientist Tom Prettyman as lead author, we have learned that Occator Crater also contains evidence for Ceres to have an icy crust. Using data acquired by the Gamma Ray and Neutron Detector (GRaND) aboard the Dawn spacecraft, Prettyman and his team, which includes several other scientists from PSI, created a detailed map of the concentrations of hydrogen in and around the crater. They found that these concentrations were elevated from what was expected, particularly in the outermost meter of the surface of Occator. This excess hydrogen could be in the form of water ice. On the surface of Ceres.

Now, Occator Crater is a, well, crater, which means it formed as the result of an impact that happened about 20 million years ago. And when a meteor hits a body with enough force to make a crater, it throws material from under the surface up into the atmosphere, of which there isn’t one on Ceres, so some of that material will fall back down to the surface while some is ejected into space. Reminder: rocks are bombarding everything, everywhere in our solar system. Some of that ejecta could even end up here on Earth as it has with Vesta.

This process is how we can now see some of the ice on the surface of Ceres. Prettyman explains: We think that ice has survived in the shallow subsurface during the roughly 20 million years following the formation of Occator. Similarities between the global distribution of hydrogen and the pattern of large craters suggest impact processes have delivered ice to the surface elsewhere on Ceres. This process is accompanied by the loss of ice by sublimation caused by heating of the surface by sunlight.

This particular impact possibly brought up material from as far down as ten kilometers below the surface. Prettyman goes on to note: The findings reinforce the emerging consensus that Ceres is a differentiated body in which ice separated from rock to form an icy outer shell and subcrustal ocean. …the findings could have implications for the evolution of icy bodies, small and large. More broadly, as an ocean world, Ceres could be habitable and is, therefore, an attractive target for future missions.

Ceres could be habitable. Wow. I don’t think Ceres is big enough for space whales, so I’m going to root for space squid instead. And I, for one, welcome our new cephalopod overlords. We really, really need to figure out how to sample the subsurface water on all these ice-covered ocean worlds, please.

More Information

PSI press release

“Replenishment of Near-Surface Water Ice by Impacts Into Ceres’ Volatile-Rich Crust: Observations by Dawn’s Gamma Ray and Neutron Detector,” T. H. Prettyman et al., 2021 July 21,