Why aren’t there large craters on Ceres? NASA weighs in.

As the largest object in the Asteroid Belt between Mars and Jupiter, the dwarf planet Ceres should have been covered in large craters – but much to their surprise, researchers analyzing data from NASA’s Dawn spacecraft found that its surface contained only smaller impact basins.

Those scientists, who reported their findings Tuesday in the journal Nature Communications, are now looking to explain why Ceres, which should have been home to 10 to 15 craters larger than 250 miles (400 km) wide and 40 more than 62 miles (100 km) wide, has just 16 craters that meet the latter criteria, none of which are larger than 175 miles (280 km) across.

Previously, Dawn analyzed the surface of the second-largest object in the asteroid belt, Vesta, and found that its surface was covered with large impact sites like those that should have been found on Ceres, according to Space.com. So why aren’t there any very large craters on Ceres?

“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,” lead investigator Dr. Simone Marchi, a senior research scientist in the Space Science and Engineering Division at the Southwest Research Institute (SwRI) in Boulder Colorado, explained in a statement.

Ceres appears to have regenerated itself, possibly due to ice content

According to Space.com, Ceres is roughly 4.5 billion years old and was in existence during the most collision-heavy period in the history of the universe, which makes it highly unlikely that it would have escaped unscathed. Dr. Marchi and his colleagues conducted hundreds of computer simulations of collisions that the dwarf planet may have existed during its lifetime.

Those simulations show the odds of Ceres having so few large craters was just 2%. So where are they? The study authors believe they have found clues explaining what might have happened in the dwarf planet’s topography. They discovered three shallow, roughly circular basins up which were up to 500 miles (800 km) wide and hidden underneath a surface with smaller craters.

Formally known as “planitiae,” these basins might have created by older, larger impacts, then covered over by material that was then exposed to impacts from smaller objects, the researchers explained. Ceres’ interior structure could explain how this occurred: if, as the evidence suggests, the upper layers of the dwarf planet contain ice, this less-dense substance could have caused the surface to smooth out more quickly than if it had been made entirely of rock. Another possibility is that cryolava may have flowed over the surface, covering up the impact sites.

“It is as though Ceres cures its own large impact scars and regenerates new surfaces, over and over,” Dr. Marchi said in a statement. “Regardless of the specific mechanism(s) for crater removal, our result requires that large crater obliteration was active well after the late heavy bombardment era, or about 4 billion years ago. This conclusion reveals that Ceres’ cratering record is inextricably linked to its peculiar composition and internal evolution.”

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Image credit: NASA JPL

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