The peculiar absence of large impact craters on dwarf planet Ceres - located in the asteroid belt between Mars and Jupiter - is linked to the planet’s internal evolution, finds a paper published in Nature Communications this week.
Craters larger than about 280 kilometers in size are known to be absent from the surface of Ceres, which is instead dominated by smaller impact craters. Collisional models of the evolution of planets from planetesimals (the building blocks of planets) predict that 10-15 craters larger than 400 kilometers should have formed on Ceres over the last 4.55 billion years. Similarly, comparison with the asteroid Vesta suggests at least six to seven craters larger than 400 kilometers should be present. Their conspicuous absence had not been explained until now.
Simone Marchi and colleagues use data from the NASA Dawn mission on Ceres to study global crater distribution and run collisional simulations of the evolution of Ceres, assuming it held its current position in the main belt over the last 4.55 billion years. Their models predict the presence of craters over 100-150 kilometers in size, but the authors find that these are mostly absent, and conclude that a significant population of large craters has been obliterated beyond recognition over geological timescales. They propose that this probably occurred as a result of Ceres’ peculiar composition and internal evolution. They propose that volcanic and topographic processes may have been responsible for the smoothening of the crater rims. In addition, rims could also be obscured by the high spatial density of smaller craters.
The authors also present topographic evidence for the presence of one - possibly two - depressions 800 kilometers in diameter that may be relict impact basins from large collisions that took place early in Ceres’ history.