Gerard Kuiper postulated the existence of a reservoir of planetary
material just outside the orbits of Neptune and Pluto and essentially confined
to the plane of the solar system, i.e., Jupiter's orbital plane [ Kuiper,
1951]. He argued that these objects are the result of the condensation of
the outer part of the Solar nebula and that their composition would be
dominated by water ice and other volatiles such as CH
, NH
, CN, CO,
etc. The first such object was discovered by Jewitt and Luu [1992] at a
distance of 41 AU and was confirmed by other observations by this team and
others. Given their estimate of the size of 250 km (based on an albedo of
0.04 which is typical of a comet nucleus), it was clearly a significant
achievement because of the very slow proper motion and the dimness of the
reflected light with a red magnitude of 22.8. The object is somewhat redder
than solar light, inconsistent with a surface of pure ice and consistent with
dirty ice. Preliminary orbital elements were computed by Brian Marsden from
the observations of Jewitt and Luu, yielding a semi-major axis of 44 Au , an
eccentricity of 0.11 and an inclination of 2.2 degrees. This object, called
1992 QB
, was found in a search of 0.7 square degrees of sky and the
authors postulate an expected number of about 1500 in the 4 degree band on the
ecliptic, all around the sky. Jewitt and Luu reported a second Kuiper object,
1993 FW in a footnote to their cited paper and have discovered several more
since then. Thus, a entirely new class of solar system objects (comets) are
available for study 40 years after Kuiper's reasoned predictions.