Context. Small binary asteroid systems and pairs are thought to form through fission induced by spin up via the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect. This process is expected to depend on their structural strength and therefore composition. Aims. We aim to determine how taxonomic classes – used as a proxy for composition – are distributed amongst binary asteroids and asteroid pairs compared to the general population. Methods. We compared the distribution of taxonomic classes of binary systems and pairs with that of a reference sample of asteroids. We built this sample by selecting asteroids in a way that reproduces the orbital and size distribution of the binaries and pairs. We did this in order to minimize potential biases between samples. Results. A strong deficit of primitive compositions (C, B, P, D types) among binary asteroids and asteroid pairs is identified, as well as a strong excess of asteroids with mafic-silicate-rich surface compositions (S, Q, V, A types). Conclusions. Amongst low-mass, rapidly rotating asteroids, those with mafic-silicate-rich compositions are more likely to form multiple asteroid systems than their primitive counterparts.

We present new speckle measurements of the position of Linus, the satellite of the asteroid (22) Kalliope, obtained at the 1m C2PU-Epsilon telescope on the Plateau de Calern, France. Observations were made in the visible domain with the speckle camera PISCO. We obtained 122 measurements in February–March 2022 and April 2023, with a mean uncertainty close to 10 milli-arcseconds on the angular separation.