Dwarf planet Ceres is just one of many objects in the Asteroid belt with a "rough" ordeal.

Considered as the largest object in the Mars-Jupiter circumstellar disc, Ceres has been struck by numerous large asteroids throughout its 4.5 billion-year history, which consequently chiseled the dwarf planet's surface.

Scientific calculations have predicted that there would be about 10 to 15 craters with a diameter of at least 250 miles (402 kilometers) and 40 craters with a diameter of at least 62 miles (99.7 kilometers) on Ceres.

But NASA's Dawn spacecraft, which began orbiting the dwarf planet in March 2015, found something different. Data from the Dawn mission revealed that Ceres is actually covered in multiple young, tiny craters, but no large craters. What happened to the large craters?

Missing Craters On Ceres

Prior to its visit to Ceres, the Dawn spacecraft examined the asteroid Vesta, which has a pockmarked appearance. Because of this, astronomers expected that Ceres would be the same.

Simone Marchi, the lead researcher at Southwest Research Institute, says Ceres has witnessed the violent early days where collisions were much more common in the solar system. This would have caused the formation of large craters.

Instead, although there are small craters on the surface, the largest impact crater was no more than 175 miles (282 kilometers) in diameter. Vesta, on the other hand, contained an impact crater with a diameter of 500 miles (805 kilometers).

Marchi and colleagues discovered that there was less than 2 percent probability of Ceres surviving through 4 billion years with its assortment of craters.

The team believes this finding points to something special about the dwarf planet. They conclude that something must have erased the marks of large craters.

What Must Have Caused The Disappearance?

The research team employed the use of computer models and the data gathered by the Dawn mission. They found signs of multiple large, round craters hiding below a surface that has been smoothed and marked up with smaller impacts.

Researchers conclude that the strange composition and internal evolution of the dwarf planet must have erased the large impact basins.

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.

While researchers have no definitive answer as to what caused the disappearance of the craters, they have two theories.

First, the layer of subsurface liquids — which is salty and icy — is possibly flowing and viscous. The substance might have allowed the craters to become smooth over time and form a new surface.

Second, ice volcanoes might have spewed out roiling water that changed the surface. Ice volcanoes may have been more active during the dwarf planet's earlier years, scientists say.

"Whatever the process or processes were, this obliteration of large craters must have occurred over several hundred millions of years," says Marchi.

Meanwhile, researchers believe that further investigations must be done to determine the internal mechanism behind the phenomenon. Details of the new study are published in the journal Nature Communications.

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