Craters on Pluto suggest Kuiper Belt ate its smaller bodies

Many of the smaller bodies that remained are products of multiple collisions and have perhaps formed and re-formed multiple times—some are little more than rubble piles barely held together by gravity.Without some knowledge of what these bodies looked like, then, it's difficult to determine whether our models of the physics of the early Solar System are right and whether similar processes are likely to be in play in exosolar systems.Now, some researchers have found a way to infer the sizes of objects present in the early Solar System: looking at the craters they left behind when they smashed into Pluto and Charon. The results suggest a shortage of objects smaller than 2km in diameter and suggest that much of the material in the Kuiper Belt was quickly swept up into larger objects, which somehow avoided smashing into each other and liberating a new generation of smaller fragments.It's relatively easy to build models of the behavior of the particles of dust and ice that orbited our then-forming Sun. And a key determinant of their possible accuracy is their ability to form planet-like objects, since we know that was the eventual fate of the Solar System. Without a sense of the size distribution of present-day Kuiper Belt objects, it's tough to figure out which of these models is closer to right.One way to get a grip on the size of the objects out there is to look at the marks they leave on other objects. And going from crater to impactor sizes means that there seem to be fewer than expected Kuiper Belt objects below 1km in diameter.