The distribution of water frost on Charon

by: Buie, M. W.; Shriver, S. K.

ABSTRACT

We present high-spatial-resolution imaging observations of the Pluto-
Charon system taken with ProtoCAM on the Infrared Telescope Facility
(IRTF). Our dataset consists of measurements from eight nights at widely
separated rotational longitudes and covering five wavelengths -- standard
J, H, and K, plus two special narrow band filters at 1.5 and 1.75 microns.
The relative flux contributions of Pluto and Charon were extracted, when
possible, by fitting a two-source Gaussian image model to the observed
images. At K, we find the Charon-Pluto magnitude difference to be on
average 1.8 mag, somewhat less than the value of 2.2 mag found by Bosh et
al. (1992). The average differential magnitude at 1.5 and 1.75 microns is
2.0 and 1.6, respectively. The larger magnitude difference at 1.5 microns
is due to a water-frost absorption band on the surface of Charon. Our
observations are consistent with a surface of Charon dominated by water
frost at all longitudes.

ICARUS vol. 108, no. 2, pt. 1 p. 225-233 April 1994