“But at Ceres, all we saw was the Kerwan Basin, just 177 miles in diameter”, co-author David Williams, director of Arizona State University’s planetary studies program, said in a statement.
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Ceres craters – In March 2015, the NASA spacecraft Dawn began orbiting the dwarf planet Ceres.
Marchi likens the phenomenon to “self-healing”, saying that it is as though the dwarf planet cures its own impact scars and regenerates a new surface over and over.
On Vesta, for example, an asteroid that is half the size of Ceres, Dawn found huge craters, including one that is 300 miles in diameter.
According to the crash simulations the team had previously done, they claimed that the dwarf planet – located between Mars and Jupiter – should have 10 to 15 craters over 250 miles in diameter.
Scientists have a few ideas as to how these craters disappeared. Blue areas are low elevation, red is high.
Credit: Southwest Research Institute/Simone Marchi.
Further study of Dawn’s images revealed that Ceres does have three large-scale depressions called “planitiae” that are up to 500 miles (800 kilometers) wide. Dawn orbited the asteroid Vesta in 2011-2012, and now it’s in orbit exploring a second world in the asteroid belt, the dwarf planet Ceres. They conclude that something must have erased the marks of large craters. Their simulations predicted that Ceres should have 90 to 180 craters that are each more than about 65 miles (100 km) wide, but Ceres appears to only have about 40 such craters.
The top image shows the size and distribution of craters on Ceres, while the bottom image shows the craters that were actually found on the dwarf planet.
“Regardless of the specific mechanism (s) for crater rim removal, our result requires that large crater obliteration was active well after the late heavy bombardment”, the study authors wrote.
“The ability to compare these two very different worlds in the asteroid belt – Vesta and Ceres – is one of the great strengths of the Dawn mission”, said lead investigator Simone Marchi, a senior research scientist at the Southwest Research Institute. “Thus, it points to something special about Ceres, something that we could not have guessed”.
Ceres is particularly interesting because it’s so big: At almost 600 miles across, this large body for some reason never managed to collect enough material to make it to full-planet status.
Another explanation may be ice volcanoes. And cryovolcanoes, which erupt in molten ice, could cover up impact sites. Recent work suggests that Ceres may consist of up to 25 percent water- ice by mass (in its interior), and so may experience cryovolcanic activity.
And finding out more about Ceres’ interior is one of the more intriguing aspects of Dawn’s continued mission there.
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Much like Star Trek’s Starship Enterprise without its shields, when you’re a planet without an atmosphere, space can be a unsafe place – especially in the earlier days of our Solar System’s formation. Over time, most of these rocks would have collided with other objects and gotten smashed to bits, leading to smaller and smaller craters on Ceres. One reason could be because large amounts of water or ice in Ceres’ interior, which has always been suspected. “There [may even be] other processes that we have not thought of”.
