  We have measured the mid-infrared thermal continua from two Centaurs,
inactive (8405) Asbolus and active 95P=(2060) Chiron, and have constrained
their geometric albedos, p, and effective radii, R, with the Standard Thermal
Model for slow rotators. These are the first such measurements of Asbolus; we
find R=33 km +/- 2 km and p=0.12 +/- 0.03. This albedo is higher than all of
those confidently known for active cometary nuclei. The thermal inertia is
comparable to or lower than those of main belt asteroids, the Moon, and Chiron;
lower than those of the icy Galilean satellites; and much lower than those of
near-Earth asteroids. For Chiron, we find R=74 km +/- 4 km and p=0.17 +/- 0.02.
While this albedo is consistent with the established value, previous radiometry
by others implied a larger radius. This effect may be partially due to a
varying infrared dust coma but all datasets have too low signal to be sure.
Four Centaur albedos (out of about 30 objects) are now known. They show a
diversity greater than that of the active comets, to which they are
evolutionarily linked.
