The recent discovery of asteroidal type objects with orbits beyond
  that of Neptune is of considerable importance and has implications
  for the study of Solar System formation. The objects are widely
  thought to form part of the "Kuiper Belt" after G.P. Kuiper who
  first suggested that progressively smaller bodies should exist
  beyond the known planets. Kuiper Belt objects (KBOs) may therefore be
  the most pristine objects in our Solar System and, in addition,
  numerical simulations indicate that they may be the source of
  short period comets. The KBOs were discovered at visible wavelengths
  and have visual magnitudes around 22. The visual magnitude gives the
  product of the cross-section and the albedo.  These parameters cannot
  however, be separated without the additional information that only
  ISO can provide. By giving the thermal emission of KBOs at
  100 microns, ISO will allow us to separate the visual albedo from the
  radius and hence obtain fundamental properties of these objects
  allowing a first comparison with the known properties of cometary
  nuclei and other small remote bodies.

  Our primary goal is to detect at least one KBO near the peak of its
  thermal emission (100 microns) using ISOPHOT.  Our secondary goal
  is to attempt to detect the objects at even longer wavelengths in
  order to solve in addition for the IR emissivity.  Our next priority
  is to survey the 7 brightest KBOs based on the assumption that,
  like cometary nuclei, the surfaces of KBOs are of very low albedo.
  Finally, we will seek to compare KBOs which might be in a
  transitional state such as 944 Hidalgo, Chiron, and 1993 HA2.