Recent studies suggest that the dwarf planet Ceres, the largest object in the asteroid belt between Mars and Jupiter, may have once contained a muddy ocean beneath its surface. This new understanding comes from advanced computer models that show Ceres’ outer crust is likely composed of a frozen, impurity-rich ocean.

Surface features that indicate the presence of ice

Ceres measures 588 miles (946 kilometers) in diameter and exhibits various surface features—pits, domes, and landslides—that imply the presence of significant ice in its vicinity below the surface. Ian Pamerleau, Ph.D. student at Purdue University, noted that spectroscopic data reveal ice beneath the dusty regolith, while measurements of Ceres’ gravity field indicate a density comparable to that of impure ice. Despite these signs, many planetary scientists remained skeptical after NASA’s Dawn mission, which provided extensive observations of Ceres between 2015 and 2018.

Observations from NASA’s Dawn mission

One of the key observations of the Dawn mission was the prevalence of clear craters with steep walls, which usually indicate a less ice-rich environment. On icy ocean worlds like Jupiter’s moons Europa and Ganymede, there are fewer large craters because the ice can flow and soften over time, making the craters less pronounced. However, Ceres showed numerous deep craters, leading researchers to conclude that its crust is not as icy as first thought.

Simulations to understand crater behavior

To investigate this further, Pamerleau, along with his Ph.D. supervisor Mike Sori and Jennifer Scully of NASA’s Jet Propulsion Laboratory ran simulations to examine how Ceres’ craters would develop over billions of years with different proportions of ice, dust and rock. Their findings suggest that a crust composed of approximately 90% ice would not be stable enough to allow significant flow, thus preserving the craters.

Implications of Ceres’ oceanic past

Mike Sori noted that Ceres probably once resembled an oceanic world similar to Europa, but with a “dirty, muddy ocean.” As the ocean froze, it formed an ice crust containing trapped rocky material. Researchers are particularly interested in determining how long this ocean could have existed, since heat from radioactive isotopes could have prolonged its liquid state after Ceres cooled.