Asteroid pairs: a complex picture

We studied 93 asteroid pairs. We estimated times elapsed since separation of pairmembers that are between 7*10^3 and a few 10^6 yr. We derived the rotation periodsfor all the primaries and a sample of secondaries. We derived the absolute magnitudedifferences of the asteroid pairsthat provide their mass ratios. We refined their WISE geometric albedosand estimated their taxonomic classifications. For 17 pairs, we determined their pole positions. In 2 pairswhere we obtained the spin poles for both components, we saw the same sense of rotation for both components and constrained the angles between their original spin vectors at the time of their separation. We found that the primaries of 13 pairsare actually binary or triple systems, i.e., they have one or two bound secondaries (satellites). As by-product, we found 3 new young asteroidclusters (each of them consisting of three known asteroidson highly similar orbits). We compared the obtained asteroid pairdata with theoretical predictions and discussed their implications. We found that 86 of the 93 studied pairsfollow the trend of primary rotation periodvs mass ratiothat was found by Pravec et al. (2010). Of the 7 outliers, 3 appear insignificant (may be due to our uncertain or incomplete knowledge), but 4 are high mass ratio pairsthat were unpredicted by the theory of asteroid pairformation by rotational fission. We discuss a (remotely) possible way that they could be created by rotational fission of flattened parent bodiesfollowed by re-shaping of the formed components. The 13 pairswith binary primaries are particularly interesting systems that place important constraints on formation and evolution of asteroid pairs. We present two hypotheses for their formation: The pairshaving both bound and unbound secondaries could be `failed asteroidclusters', or they could be formed by a cascade primary spin fission process.