(Click to enlarge)
Some brief off-the-top-of-my-head thoughts on this image of Pluto.
After all the talk about Pluto's surface having a surprising dearth of cratering I realized on looking at the above image that scientists were talking in relative terms; the picture actually shows Pluto to be quite pock marked with craters - however, a lot less so than that of the Moon and other planets, but probably much more so than the Earth. Ergo, Pluto's surface is older than that of the Earth which, of course, is subject to high levels of largely atmospheric based erosion and change. In fact the crater density of Pluto may be comparable to that of the Lunar Mare. (See the hi-res picture of Pluto on the web site below)
Pluto has a thin atmosphere as this picture shows:
Pluto's size, along with its inclined and eccentric orbit may be evidence that it is a captured Kuiper belt object; perhaps an outcome of the long term gravitational chaos of the Solar System. If the once very frozen Pluto was relatively recently captured into its current orbit then its solar constant would change. Such orbital change could conceivably result in the low boiling point of some of Pluto's surface compounds just being passed, consequently creating an atmosphere and in turn starting off a slow erosion cycle. This may explain Pluto's relatively "young" surface. But remember; in Solar System terms half a billion years is "young"!
Anyway, be all that as it may, we had better wait and see what the experts say. One thing is clear: Given the number of unknowns there is plenty of theoretical scope to explain the appearance of Pluto!
For more pictures of Pluto see: