Vesta: Spin Pole, Size, and Shape from HST Images

Abstract

HST images obtained over an interval of 71 hr at a scale of 52 km/pixel have been used to determine the spin pole, size, and shape of Vesta. Several bright and dark surface features allow control point stereogrammetric measurement of spin pole orientation. An independent solution of spin pole and shape can be made from the limb and terminator coordinates. A combined control point and limb solution for Vesta's rotation pole is at α₀= 308° ± 10°, δ₀= 48° ± 10°, J2000). Its shape can be fit by an ellipsoid of radii 280, 272, 227 (±12) km. The mean density of Vesta from the mass reported by Schubart and Matson (1979) is 3.8 ± 0.6 gm/cm³. For this density Vesta's shape is close to that of a Maclaurin spheroid with superposed variations of ∼15 km.