IRAS observations of the Pluto-Charon system

by: Aumann, H. H.; Walker, R. G.

ABSTRACT

High-signal-to-noise-ratio observations of the Pluto-Charon system at 25,
60, and 100 microns using IRAS are combined with visual-magnitude and
mutual-eclipse constraints to evaluate thermal models of Pluto and Charon.
These models are consistent with eclipse observation by Dunbar and Tedesco
(1986) but not with Reinsch and Pakull (1987). The most likely model for
Charon is the standard asteroid model, typical for the icy Galilean and
Saturnian satellites. Charon models with a significant atmosphere can be
ruled out. Based on currently available radius and albedo constraints, no
significant numerical distinction is possible between Pluto models ranging
from isothermal spheres with surface emissivity between 0.4 and 0.9.
Concerns regarding the viability of an emissivity as low as 0.4 favor the
higher-emissivity models. The globally uniform surface temperature of
Pluto may thus at present be as low as 45 K, with a methane column abundan-
ce of 6.7 cm atm. The most likely models are centered on radii of 1180
and 747 km and albedos of 0.47 and 0.26 for Pluto and Charon, respectively.

Astronomical Journal, ISSN 0004-6256, vol. 94, Oct. 1987, p. 1088-1091.