Determining the surface temperatures of Pluto and Charon places strong constraints on the types of ices stable on their surfaces. This in turn yields information on the composition of these bodies, and constrains models of solar system formation. Previous radio, millimeter, and submillimeter wavelength observations have not spatially resolved the pair (which have a maximum separation of just 0.9''), and have produced contradictory results regarding their surface temperatures. On 21 June 2005 we utilized the Submillimeter Array (SMA) in its most extended configuration to observe the Pluto-Charon system at 220 GHz (1.36 mm). With baselines up to 509 m, these observations achieved a resolution of ˜0.4'', allowing for the first time a direct measure of the thermal emission of each object separately. Direct visibility fitting of the data show the flux densities of Pluto and Charon to be 10.8±1.0 mJy and 3.6±1.0 mJy, respectively. Disk average Planck brightness temperatures (after a small correction for the CMB) are 38.0±3.0 K (Pluto) and 50±12 K (Charon). Assuming average surface emissivities of 0.9±0.1, these convert to average physical surface temperatures of 42±4 K for Pluto, and 56±14 K for Charon. These results are consistent with a model of Pluto's surface being 90±30% covered with N2 ice at 40 K, and Charon's surface being in equilibrium with solar insolation.
AAS/Division for Planetary Sciences Meeting Abstracts #37
- Pub Date:
- August 2005