Presentation #307.01 in the session “Centaur/KBO/Pluto Gathertown”. Cross-listed as presentation #111.04.
In addition to its 3500 km flyby of Kuiper belt object (KBO) (486958) Arrokoth, NASA’s New Horizons spacecraft has observed more than 30 other KBOs and dwarf planets at viewing geometries unattainable from Earth. Several of these KBOs, like Arrokoth, are members of the dynamically cold classical (CC) population; therefore, the New Horizons observations of these objects at high solar phase angles provide important context to place Arrokoth among other small CC KBOs (HV = 8-11) in terms of their rotation rates, rotation pole orientations, shapes, and surface scattering properties. New Horizons observed CC KBOs 2014 PN70, 2014 OS393, 2011 HF103, 2011 JY31, and 2011 JX31 from distances as small as 0.09 AU at multiple solar phase angles between 19 and 122 degrees. Rotation rates range from 12.05 hours for 2014 PN70, near Arrokoth’s 15.92-hour period (Stern et al. 2019, Science 364, aaw9771), to more than 35 hours for 2014 OS393 and 2011 JY31. The amplitudes of most CC KBO rotation curves increase with increasing solar phase angles, likely due to their irregular shapes. Binary CC KBO 2011 JY31 (Porter et al. 2020, BAAS 52, 307.03; Weaver et al. 2021, in preparation), however, has a low-amplitude (0.2 magnitudes) rotation curve that does not increase in amplitude with increasing phase angle (Verbiscer et al. 2019, AJ 158, 123). All CC KBOs have steep solar phase curves and small phase integrals, much like those of other small, dark asteroids, comet nuclei, and satellites.