Ceres, the largest object in the asteroid belt between Mars and Jupiter, should be riddled with craters. But when NASA's Dawn spacecraft started orbiting the dwarf planet last year, scientists were surprised to find it was relatively smooth. In a study published this week, researchers conclude that something mysterious must have erased the marks. Given the pockmarked appearance of most asteroid belt objects — including Vesta, the asteroid that Dawn visited before arriving at Ceres — scientists expected many large craters to pepper their planetary target. Instead, while many small craters mark up the surface, the largest impact crater they found was just 175 miles across. In contrast, Vesta — half the size of Ceres — has a whopper of an impact crater some 500 miles wide. When they crunched the numbers, team of researchers found that there was a less than 2 percent chance of Ceres getting through 4 billion odd years with the assortment of craters it seems to sport. With the help of computer models and data from Dawn, they concluded that the "peculiar composition and internal evolution" of Ceres must have erased larger impact basins somehow. The researchers found signs of multiple large, circular craters hiding just below a surface smoothed and marked up with smaller impacts. The researchers can't be sure yet exactly how Ceres managed to turn back the clock and achieve this youthful look. But they're floating two ideas: Briny, subsurface liquids and ice volcanoes. https://www.washingtonpost.com/news...s-is-mysteriously-missing-a-bunch-of-craters/ Study: http://www.nature.com/ncomms/2016/160726/ncomms12257/full/ncomms12257.html
Ceres may lack craters, but it has warm hart, according to the recent research. Under the surface of the dwarf planet are strange jumbled zones that are mixes of ice and rock. The research suggests that Ceres might still be warmed by radioactive material in its interior. Previous remote analysis of Ceres using ground- and space-based telescopes suggested that it was not as dense as other large asteroids such as Vesta. This suggested that Ceres was not made up solely of rock, but composed partly of both icy and rocky material. However, scientists weren't sure how the innards of Ceres were structured. Whereas Earth developed an onion-like structure fully differentiated into distinct layers — an outer crust, a central core and a mantle layer between the two — prior research suggested that Ceres might only be partially differentiated into more vague zones, or perhaps not differentiated at all. Shedding light on the structure of Ceres might, in turn, yield insight into how it and other asteroids and dwarf planets evolved over time. http://www.space.com/33635-dwarf-planet-ceres-interior-layers-revealed.html
