Harpalyke belongs to the Ananke group, believed to be the remnants of a break-up of a captured asteroid. It is about 4 kilometres in diameter and appears grey similar to C-type asteroids. The moon orbits Jupiter at an average distance of 21,064,000 km in 624.542 days, at an inclination of 147° to the ecliptic (147° to Jupiter's equator) with an orbital eccentricity of 0.2441.