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Constraining Thermal Emission of Pluto’s Haze From Infrared Rotational Lightcurves

Presentation #308.06 in the session Pluto System (Oral Presentation)

Published onOct 23, 2023
Constraining Thermal Emission of Pluto’s Haze From Infrared Rotational Lightcurves

The rotational lightcurves of the Pluto-Charon system were previously believed to be solely attributed to their surfaces. However, a proposed scenario of haze cooling (Zhang et al. 2017) suggests that the atmospheric haze of Pluto could significantly contribute to mid-infrared emission, which calls for a revisit of previous analyses. In this study, we employ a Bayesian retrieval approach to constrain the haze emission from the rotational lightcurves of the Pluto-Charon system. The lightcurves were observed by the Spitzer and Herschel telescopes and the retrievals were combined with the latest surface albedo maps of Pluto and Charon from the New Horizons spacecraft. Our results show that including the haze emission is consistent with all previous observations, with the best-fit haze flux around 1-2 mJy. This is in agreement with the composition of Titan-like hazes. However, the surface-only model can still explain the observations roughly well. We conclude that the Spitzer and Herschel data cannot constrain Pluto’s haze emission due to the degeneracy with Charon’s surface emission. Regardless, some surface properties of Pluto can be constrained such as the thermal inertia and CH4 ice emissivity. We suggest that observations in the other wavelengths such as 18 microns by JWST, which can resolve Pluto from Charon, could directly probe the haze emission of Pluto and might detect the rotational light curves of Charon.

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