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Description
Asteroids comprise of material left over from the early days of the formation of the Solar System. Studying their physical composition and dynamical evolution are among the best evidence for the initial conditions and dynamical evolution of the Solar System. Asteroids come in sizes from metres up to hundreds of kilometres. Currently, essentially no data exist on the very small asteroids originating from the outer belt. However, the flux of the asteroids from the main belt into the near-Earth asteroid (NEA) population gives a unique opportunity to probe this virtually unstudied population through close flybys of NEAs. The steady-state population of NEAs with large $a$ originate from the source regions in the outer main belt (Granvik et al. 2018), such as 2:1 and 5:2 mean-motion resonances with Jupiter, as well as objects on Jupiter-family-comet-like orbits. Advancements in the asteroid surveys, such as Catalina Sky Survey, Pan-STARRS and ATLAS as well as data from Hayabusa 1 and 2 and OSIRIS-ReX missions have recently brought the smallest asteroids, with diameters less than 50 m, within reach of feasible research. While many smallest asteroids have been characterised by the ongoing MANOS survey (Devogèle et al. 2019), their sample selection is constrained to mission-accessible asteroids, limiting their sample orbital space with relatively small $e$ and $i$, with higher probability to originate from the inner main belt.
Despite the scarce observations, there are several indications that the taxonomic distribution of smallest asteroids is different from that of the larger ones. By observing smallest asteroids we are characterising the undividable building blocks of larger asteroids, which are gravitational aggregates. The fast rotation periods of smallest asteroids (Warner et al. 2009) imply their monolithic structure. 1-20 metre-sized monolithic boulders are abundant on the surfaces of larger asteroids such as (162173) Ryugu (Hayabusa2 mission; Tatsumi et al. 2021) and (101955) Bennu (OSIRIS-ReX mission; DellaGiustina et al. 2021).
We present the preliminary results of an ongoing campaign with ALFOSC/NOT to provide a statistically significant sample of very small asteroids originating from the outer main asteroid belt.