- Roughly 10 billion icy objects outside the orbit of Neptune. -
Although believed to exist since 1930's, only discovered in 1992
because objects are far away and thus faint. - Most of the
bright KBOs are the same as a 100 watt light bulb on the Moon. -
Exception is Pluto because it is covered by bright frost and so
reflects 90% of sunlight. - Objects like the Moon reflect only a
few percent. - That is why scientists originally believed that
Pluto was much bigger than it is.