 Every 18 years, the asteroid 197 Arete approaches within of Vesta.In 1966, based upon observations of Vesta's gravitational perturbations of Arete, Hans G. Hertz estimated the mass of Vesta as solar masses.More refined estimates followed, and in 2001 the perturbations of 17 Thetis were used to estimate the mass of Vesta as solar masses.