<If we don't detect them, where do his numbers come from to support the assertion that they exist, at all?"

What Lurks In The Outer Solar System?

["Based on our surveys we think there are about 70,000 KBOs larger than 100 km across between 30 and 50 AU from the Sun," says Jewitt. If you added all of them together they would form a planet about one-tenth the mass of Earth. The Kuiper Belt is about 300 times more massive than the asteroid belt between Mars and Jupiter, he added.

Finding even 400 or so KBOs among the tens of thousands beyond Neptune is impressive. These faraway objects are surprisingly dark. Although they're icy, explains Jewitt, "most KBOs reflect about as much sunlight (4 - 7%) as a lump of charcoal." It's because of cosmic ray bombardment, which darkens and reddens their surfaces by breaking the bonds of molecules in the ice -- molecules that reform as complex carbon-based compounds. The organic goop makes good camouflage against the black of space.]

http://www.spacescience.com/headlines/y2001/ast13sep_1.htm
---

[And T. Denk reported that a careful reexamination of Voyager's photos of Saturn's strange moon Iapetus -- which has a very dark-colored leading side and a light-colored trailing side -- suggests that, despite being 1500 km in diameter, it is surprisingly non-spherical, with a radius ranging from 713 to 767 km, which makes it "quite unusual in the Solar System".

He also says that the dark layer appears to be so thick that it could not be made of material blasted off Saturn's tiny outermost moon Phoebe (which is definitely a captured carbonaceous asteroid) -- and that it may instead be the remains of an ancient moon of Saturn between Iapetus and Phoebe that was shattered by an impact with an asteroid or still another moon, and then gradually sprinkled onto Iapetus' leading side.

In other areas, B. Hapke provided more evidence that the mystery of the origin of most meteorites -- which don't seem to match the mineral spectra of any asteroids -- can be explained by the "space weathering" of the surfaces of asteroids by the chemical effects of the solar wind on their surfaces over billions of years (with the meteorites being more recently broken off their parent bodies and thus having "fresher" surfaces).]

http://www.spacedaily.com/news/lunarplanet-2000-00d3.html

Very possible that Iapetus came from the KB as well as other low albedo(ancient comets?) NEOs.

Marcia