Emission from Pluto and Charon at Long Wavelengths: Observations using ALMA, SMA, and VLA

We report on the first Earth-based observations of thermal emission from the surfaces of Pluto and Charon where the two are resolved from each other. Observations at wavelengths from 0.8 mm to 0.9 cm with the Atacama Large Millimeter/submillimeter Array (ALMA), Submillimeter Array (SMA), and Karl G. Jansky Very Large Array (VLA) provide separate, high SNR flux densities for both bodies, which are converted into brightness temperatures. These observations have been presented separately previously [1-3] but here we combine them for the first time and extend the analysis. For Pluto, brightness temperatures range from 31--33 K, and for Charon from 42--45 K, over the full range of observed wavelengths. These brightness temperatures are significantly lower than observed surface temperatures for both bodies. While hinted at from unresolved observations of the pair, this is the first definitive observation showing both bodies have depressed brightness temperatures. These low brightness temperatures are likely due to a combination of low thermal inertia, and subsurface scattering, with a larger depression for Pluto than for Charon.[1] Butler et al. 2015, BAAS #47, id.210.04. [2] Gurwell et al. 2011, DPS/EPSC, p271. [3] Butler et al. 2011, DPS/EPSC, p. 1670.