No tiny craters
Astronomers have examined images taken on both sides of Pluto and Charon, but have concentrated their most detailed investigations on the planitia vulcaine of Charon, a vast plain that resurfaced at the beginning of its history. The smooth icy surface facilitates the counting of craters, although the researchers point out that they get similar results – although less clear – from other areas of Charon and Pluto. They found that even though there were a lot of large and medium-sized craters, there was little less than 8 miles wide. Since the size of the crater depends largely on the size of the impactor, this results in a lack of impactors less than 1 mile in diameter.
Of course, small craters could simply be erased over time. But Kelsi Singer, lead author of the forthcoming research on March 1 in Science, says that this does not seem to be the case here. "We do not know anything that can erase a 10-kilometer crater, but do nothing for an 11-kilometer crater," she says. "You would see the fatter at least partially eaten. And we do not see anything that is partially filled. That's what led his team to assume that the little craters were never there.
It was a surprise, because originally, astronomers thought that the Kuiper belt would look a lot like the asteroid belt that gravitates around Mars and Jupiter. As they are much closer, astronomers better understand the asteroid belt and know that it contains many smaller objects. Many of these tiny asteroids are formed when larger asteroids hit each other and break into smaller pieces.
The Kuiper belt is much farther away, which makes it more difficult to direct observation at the telescope. The story of the impact of some of Jupiter's and Saturn's moons had left a glimpse of the lack of small bodies in the past, but since they had more active surfaces that could erase craters of all sizes, the results were less clear. .
Singer and his team believe that the Kuiper belt might look different because it is less active – it crashes less often – thus avoiding the cascade of smaller bodies produced by the asteroid belt. But in reality, these new observations require more careful observations of the Kuiper belt itself.
New Horizons is still at work and his recent meeting with Ultima Thule, further down the Kuiper Belt, seems to corroborate Singer's findings on Pluto and Charon. But more investigation is needed to understand the complete history of the Kuiper Belt.