90 Antiope
Each asteroid is about 86±1 km across, with their centers separated by only about 170 kilometers. This means that the space separating the two halves is only 60 km, or so. The two bodies orbit around the same center of mass which lies in the space between them. The orbital period is about 16.50 hours, the eccentricity below 0.03 (best estimate 0.01 ± 0.02). Every several years, a period of mutual occultations occurs when the asteroid is viewed from Earth. Using Kepler's third law, the mass and density of the asteroids can be derived from the orbital period and asteroid sizes.