Presentation #105.01 in the session Physical Properties of Centaurs & KBOs.
The New Horizons Spacecraft encountered the Kuiper Belt Object (KBO) Arrokoth on the first day of 2019. The Radio Science Experiment (REX) on New Horizons performed radiometry measurements of the KBO’s thermal emission at λ = 4.2 cm during approach on the dayside and also during departure on the nightside. Owing to the small size of the target, only a global estimate of the mean brightness temperature was possible. A brightness temperature Tb = 29 ± 5 K was derived for the nightside observation, less than Arrokoth’s predicted surface equilibrium temperature of ~50 K on the dayside. An estimate of Tb on the dayside was not possible due to unexpectedly large variations in the REX system temperature. A comprehensive model of KBO Arrokoth is used to constrain the global values of emissivity, thermal inertia and electrical skin depth of the KBO. In particular, models with small values of thermal inertia and small values of electrical skin depth can be excluded. High values of the effective radio emissivity (Eeff > 0.8) provide better agreement with the REX observation.