Abstract

I will overview recent observational data we have got for main-belt asteroid (MBA) binaries with primary diameters between 3 and 10 km. A debiasing of data obtained within the BinAstPhotSurvey shows that a fraction of binaries among small MBAs is at least as abundant as that among NEAs (~15%). Both primary rotation and orbital periods distributions of MBA binaries are broader than those of NEA binaries, both in directions towards longer periods. Equatorial elongations of primaries of MBA binaries are similarly low, with observed lightcurve amplitudes <0.28 mag, as those of NEA binaries; secondaries in both binary populations show a broad range of elongations. I will show a few anomalous cases where we see third lightcurve components; they may be a rotation of unsynchronous secondary or of another (second) satellite. Total angular momentum of binaries with orbital periods shorter than 100 hours is close to the critical limit for a single body in a gravity regime, but a couple systems with orbital periods >100 h have a higher total angular momentum.