Discovering Ceres: Where Are All the Large Craters?

Blue areas represent zones of permanent shadow Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

What’s missing? Big Craters Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

One of the many surprising discoveries made by NASA’s Dawn spacecraft in orbit over Ceres is that the dwarf planet has fewer large craters than might ordinarily be expected. As the largest target in the shooting gallery which is the main asteroid belt where Ceres resides, it should be bear the scars of numerous large impacts.

According to a paper published in Nature Communications, the fact that it doesn’t suggests to the authors that Ceres was either a late arrival to the asteroid belt from somewhere beyond the orbit of Neptune, or more likely, has some ongoing geological activity which acts to “smooth” its surface.

Abstract:

“Asteroids provide fundamental clues to the formation and evolution of planetesimals. Collisional models based on the depletion of the primordial main belt of asteroids predict 10–15 craters >400km should have formed on Ceres, the largest object between Mars and Jupiter, over the last 4.55Gyr. Likewise, an extrapolation from the asteroid Vesta would require at least 6–7 such basins. However, Ceres’ surface appears devoid of impact craters >~280km. Here, we show a significant depletion of cerean craters down to 100–150km in diameter. The overall scarcity of recognizable large craters is incompatible with collisional models, even in the case of a late implantation of Ceres in the main belt, a possibility raised by the presence of ammoniated phyllosilicates. Our results indicate that a significant population of large craters has been obliterated, implying that long-wavelength topography viscously relaxed or that Ceres experienced protracted widespread resurfacing.”

 

 

 

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