The New Horizons Mission to Pluto and Charon may also be sent to investigate other Kuiper Belt Objects. Science theory suggests KBO's are icy left over remains (mostly comets?) from the formation of the planets in our Solar System.
Pluto belongs to a third category that could be called "ice dwarfs." They have solid surfaces but, unlike the terrestrial planets, a significant portion of their mass is icy material (such as frozen water, carbon dioxide, molecular nitrogen, methane and carbon monoxide).
Pluto and Charon are also widely considered to be among the largest objects in the Kuiper Belt, a vast reservoir of icy objects located just outside of Neptune's orbit and extending out to about 50 astronomical units from the Sun. The Kuiper Belt is thought to be the source of most short-period comets - those with orbits shorter than 200 years - so scientists really want to compare the composition and surface properties of Pluto and its moons to those of cometary nuclei.
Science Overview - NASA's New Horizons Mission
Icy Kuiper Belt Objects?
If Pluto and Charon are very different to what is expected, the other Kuiper Belt Objects are not the icy mountains that is suggested, comet 67P also is not what is expected then could there be another explanation for their formation? Should there be another theory for their formation, not reliant on the old theories that did not predict?
And then what of the Oort Cloud theory - no evidence that it exists but totally reliant on the other theories?