Ceres, a dwarf planet, is the so-called queen of the asteroid belt–or, the region in the solar system with numerous irregularly shaped objects. Located in between the orbits of Mars and Jupiter, the circumstellar disc holds about hundreds of thousands of known asteroids, and there are possibly millions to billions which are still unknown.
Therefore, Ceres, the largest object in there, should have large craters, right?
This week, a NASA article published online surprised many including scientists. For starters, the spherical asteroid belt object holds many craters, but it lacks some: the larger ones. None are larger than one-hundred and seventy-five miles in diameter, NASA revealed. And to scientists, it is a huge mystery, and the reason is that Ceres is four point five billion years old already, and it must have been hit by numerous large asteroids.
When NASA’s Dawn spacecraft arrived to the orbit of the dwarf planet in March last year, scientists have easily spotted many craters, but none that resemble those in the asteroid Vesta. Now, a study published in the journal Nature Communications is trying to provide a solid answer to the mystery.
Cutting to the chase, Ceres, scientists say, has experienced significant geological evolution, thus possibly erasing the large craters created by past large collisions. It also suggests that the interior structure and the geological history of the dwarf planet are more complex that scientists have previously thought.
In an interview with the space agency’s publication, lead investigator Simone Marchi who is also a research scientist at the Southwest Research Institute in Boulder, Colorado, explains that a significant population of large craters of the small planet has been obliterated beyond recognition over geological time scales, and it was the result of its peculiar composition and internal evolution.
For the study, Marchi and the team modeled collisions of other bodies with Ceres since its formation, and it yielded results that predict the number of large craters that should have been present on its surface.
The team’s data show that Ceres should have up to ten to fifteen craters larger than two-hundred and fifty miles–or about four-hundred kilometers–in diameter, and at least forty craters larger than sixty miles or about one hundred kilometers wide. However, the data from the NASA spacecraft confirm that Ceres only has sixteen craters larger than sixty miles and none larger than one-hundred and seventy-five miles across.
An idea was also given, and it claims that Ceres originally formed farther out in the solar system, perhaps near the gas giant Neptune–or, perhaps near Pluto, and it only migrated into its present location. However, scientists say that even if the dwarf planet is a migrant object, it should still have a significant number of wide craters.
Whatever the processes were, Marchi says the obliteration of the larger craters must have occurred over several hundred million of years.
As mentioned already, Ceres differs from Vesta, a protoplanet and a member of the asteroid belt, in terms of cratering. Vesta is only half the size of the dwarf planet and yet it has a well-preserved three-hundred-mile-wide crater which scientists call Rheasilvia.
NASA’s Dawn space probe–which costs US$446 million–left Earth on September 27, 2007. It first arrived to Vesta’s orbit on July 16, 2011, and to the vicinity of Ceres last year.