Image: A grazing view of Ceres' largest well-preserved 174-mile wide impact crater, Kerwan, near the limb. Blue areas are low elevation, red is high. Kerwan gradually degrades moving toward the terminator into a 500-mile diameter, 2.5-mile deep pit, possibly a relict impact from the dwarf planet's distant past. Credit: Southwest Research Institute/Simone March Ceres, the largest object in the asteroid belt, is surprisingly lacking in large impact craters, a finding that speaks volumes about the inner workings of the dwarf planet and its evolution over time, a new study shows.
Based on computer models, scientists had expected NASA's Dawn spacecraft to find 10- to 15 craters that were 250 miles in diameter or larger on the surface of Ceres.
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Instead, Dawn, which has been orbiting Ceres since March 2015, found just 16 craters larger than 62 miles and nothing larger than 175 miles in diameter, according to a study published in this week's Nature Communications.
On Vesta, for example, an asteroid that is half the size of Ceres, Dawn found gigantic craters, including one that is 300 miles in diameter.
Ceres didn't escape being bashed. Instead, scientists believe that Ceres' large craters were erased over time by subsurface icy slush, or that they were filled with icy lava from erupting ice volcanoes.
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An analysis of images taken by Dawn shows what may be relics of one or two ancient large craters beneath a surface pitted with smaller, more recent impacts.
The mostly circular, shallow basins could be as large as 500 miles wide, Simone Marchi, a planetary scientist with the Southwest Research Institute in Boulder, Colorado, and colleagues conclude in the new study.
"These depressions may be 'relict' impact basins, left over from large collisions that took place early in Ceres' history," Marchi said in a press release.
"It is as though Ceres cures its own large impact scars and regenerates new surfaces, over and over," he said.
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