Protoplanet Ceres – one of the most primitive celestial bodies in our solar system, which is estimated to have originated about 4.55 billion years ago – hides a few surprises. A recent study conducted by an international team of researchers led by Simone Marchi from the Southwest Research Institute of Boulder (Colorado, United States) and affiliated to the National Institute of Astrophysics (INAF) – showed that the craters on its surface are far lessthan expected. The research team that carried out the study has come to this conclusion using data on the size and distribution of craters on the surface of the dwarf planet from DAWN spacecraft, which had been launched by NASA with the purpose of exploring Ceres and Veste, two very primitive celestial bodies which formed in the nascent solar system, both located in the asteroid belt.

According to the most qualified theoretical models, Ceres – having gone through the most violent phase of the period at the highest risk for collisions of the Solar system – should have up to 10 to 15 craters larger than 400 kilometres, and at least 40 craters larger than 100 kilometres. However, the massive asteroid, despite being covered in countless small craters from bigger impacts, only has 16 craters larger than 100 kilometres, and none is larger than 280 kilometres in diameter. This evidence is in sharp contrast with previous images of asteroids, including those collected by DAWN spacecraft of Vesta asteroid, which is only half the size of Ceres but has huge craters, one of which is large approximately 500 kilometres, and which completely covers the asteroid’s hemisphere. “We concluded that a significant population of large craters on Ceres has been obliterated beyond recognition over geological time scales, which is likely the result of Ceres' peculiar composition and internal evolution,”, said lead investigator, Simone Marchi, an astrophysicist from Lucca, currently researcher at the Space Science and Engineering Division of the Southwest Research Institute, in Boulder (Colorado, United States) and affiliated to INAF.

The researchers think that Ceres is able to “heal its own scars”. This hypothesis is suggested by some clues regarding the presence of three large basins, up to 800 kilometres wide, which could be hidden under a surface of myriads of small craters. “These depressions - or planitiae – could be the remains of big collisions occurred at the beginning of Ceres’ history”, suggested Marchi. This would mean that, in the past, the huge craters anticipated by the model were indeed present on Ceres’ surface. “Somehow Ceres has healed its largest impact scars and renewed old, cratered surfaces”. It is not clear how this process has occurred. “Whatever the specific process, our study shows that this obliteration process of large craters must have been still ongoing after the period of most intense bombing, about 4 billion years ago. This result shows that the traces of the presence of craters are indissolubly associated with the particular internal composition and evolution of Ceres” concluded Marchi.

Source: ResearchItaly