The dwarf planet Ceres is covered in numerous small, young craters that have scientists scratching their heads. The dwarf planet was likely hit by numerous large asteroids over its lifetime — but where did all the large craters go?

A recent study explores with the use of data from NASA’s Dawn spacecraft, which has been circling Ceres since March 2015.

"We concluded that a 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 Simone Marchi told NASA.

Marchi and her colleagues modeled collisions of other bodies with Ceres since it formed 4.5 billion years ago and predicted that the dwarf planet should have up to 10 to 15 craters larger than 250 miles in diameter and at least 40 craters larger than 60 miles wide. Their results showed that Ceres only has 16 craters larger than 60 miles and none exceeding 175 miles across.

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One theory about Ceres’ formation is that is formed farther out in the solar system, possibly near Neptune, before migrating to its current position, according to NASA. However, scientists determined that, even if Ceres made its way into the main asteroid belt somewhat late in solar system history, it should still have a significant number of large craters.

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

The images of Ceres showed that it has at least three large-scale depressions called "planitiae" that are up to 500 miles wide. These planitiae have craters in them that formed more recently, but the larger depressions could be left over from bigger impacts.

One of them, Vendimia Planitia, is a sprawling area just north of the Kerwan crater, which is Ceres' largest and most well-defined impact basin. The researchers believe Vendimia Planitia formed much earlier than Kerwan.

Another theory about the lack of large craters could be related to the interior structure of Ceres.

Previously taken images from Dawn show that . Because ice is less dense than rock, the topography could smooth out more quickly if ice or another lower-density material like salt dominates the makeup of the subsurface.

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Another analysis of the center of Ceres' Occator Crater suggests that , and that liquid water could have been present in Ceres' interior. Past hydrothermal activity that may have influenced the salts rising to the surface at Occator could also have something to do with the disappearance of the larger craters.

If Ceres had widespread cryovolcanic activity in the past, like the eruption of volatiles such as water, these cryogenic materials could have flowed across the surface, possibly burying pre-existing large craters, according to NASA. Smaller impacts would have then formed new craters on the resurfaced area.

“Somehow, Ceres has healed its largest impact scars and renewed old, cratered surfaces," said Marchi.

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