The estimate that this area is very new based on the fact that there are no meteor craters assumes that we know the distribution of meteors and space debris in the outer solar system. Does anyone know if we do in fact know this?
It seems plausible that there would be far fewer things at that distance, so the frequency of collisions would be lower.
They determine what they expect on Pluto by looking at the most cratered parts of Pluto. It is model-dependent. There are other assumptions involved, such as the distribution of crater sizes.
I believe that NASA expected lots of craters on Pluto due to its close proximity to the Kuiper Belt, which is full of asteroids and other small objects.
Similarly, the asteroid belt is "full of asteroids" that are mostly only a few meters across, with an average distance between each asteroid of a few million kilometers.
how does Pluto's inclined orbit (https://en.wikipedia.org/wiki/File:Plutoorbit1.5sideview.gif) affect its exposure to other Kuiper Belt objects? Is it still well within the cloud of objects at its greatest points of divergence from the ecliptic?
1. If it is reasonable to expect fewer collisions over time, as earlier collisions eject some objects from the belt and remaining objects settle into "safer" orbits?
2. Whether collisions cause objects to break apart such that subsequent collisions are with smaller objects, which then leave fewer discernible impacts?
3. Whether the temperature changes induced by Pluto's orbit--which cause the methane ice to move between the atmosphere and the surface--would cause a smoothing effect over time; e.g. craters being filled by reforming ice?
It seems plausible that there would be far fewer things at that distance, so the frequency of collisions would be lower.