Dwarf planet Ceres once hosted a muddy ocean beneath its icy surface

Recent studies suggest that the dwarf planet Ceres, the largest object in the asteroid belt between Mars and Jupiter, could once have had a muddy ocean beneath its surface. This new insight comes from advanced computer models that indicate that Ceres’ outer crust is likely composed of a frozen ocean rich in impurities.

Surface features indicating the presence of ice

Ceres is 946 kilometers across and exhibits several surface features – pits, domes and landslides – that indicate the presence of significant ice in the nearby subsurface. Ian Pamerleau, a 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 similar 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

A key observation from the Dawn mission was the presence of several steep-sided craters, which generally indicate a less ice-rich environment. On icy ocean worlds such as Jupiter’s moons Europa and Ganymede, there are fewer large craters because ice can flow and soften over time, making craters less pronounced. However, Ceres showed numerous deep craters, leading researchers to conclude that its crust was not as icy as originally thought.

Simulations to understand crater behavior

To investigate this further, Pamerleau, in addition to his Ph.D. supervisor Mike Sori and Jennifer Scully of NASA’s Jet Propulsion Laboratory ran simulations to investigate how Ceres’ craters would evolve over billions of years with varying amounts of ice, dust and rock. Their findings suggested that a crust composed of about 90% ice would not be stable enough to allow significant flow, which would preserve the craters.

The implications of Ceres’ oceanic past

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