Yes, there are questions:

On irradiation:

Voyager 2 found radiation belts at Uranus of an intensity similar to those at Saturn, although they differ in composition. The radiation belts at Uranus appear to be dominated by hydrogen ions, without any evidence of heavier ions (charged atoms) that might have been sputtered from the surfaces of the moons. Uranus's radiation belts are so intense that irradiation would quickly darken (within 100,000 years) any methane trapped in the icy surfaces of the inner moons and ring particles. This may have contributed to the darkened surfaces of the moons and ring particles.

From: http://vraptor.jpl.nasa.gov/voyager/vgrur_fs.html

Why are KBOs red?

Interesting reading:
Evidence of (nearby) Supernova Explosions (during the last 10my).

The Origin of the Local Bubble.

Levison has a strong point when it comes to comet ratio, etc. There is some evidence of chaos, however.

Marcia