Mean radius and shape of Pluto and Charon from New Horizons images

Abstract

Approach images taken by the LORRI imaging system during the New Horizons spacecraft encounter have been used to determine the mean radii and shapes of Pluto and Charon. The primary observations are limb locations derived using three independent approaches. The resulting mean radii of Pluto and Charon are 1188.3 +/- 1.6 km and 606.0 +/- 1.0 km, respectively (2-sigma). The corresponding densities are 1854 +/- 11 kg m-3 and 1701 +/- 33 kg m-3 (2-sigma). The Charon radius value is consistent with previous Earth-based occultation estimates. The Pluto radius estimate is consistent with solar occultation measurements performed by the ALICE and Fine Sun Sensor instruments on New Horizons. Neither Pluto nor Charon show any evidence for tidal/rotational distortions; upper bounds on the oblateness are <0.6% and <0.5%, respectively.