Size distributions of bluish and reddish small main-belt asteroids obtained by Subaru/Hyper Suprime-Cam

TL;DR

This study used Subaru's Hyper Suprime-Cam to analyze over 3,000 small main-belt asteroids, revealing similar size distributions for bluish and reddish types, supporting the rubble-pile structure hypothesis.

Contribution

First large-scale survey comparing size distributions of bluish and reddish asteroids, showing compositional differences do not significantly affect impact strength in the 0.4-5 km range.

Findings

Size distributions of C-like and S-like asteroids are similar in 0.4-5 km range.

Results support the rubble-pile structure hypothesis for small asteroids.

Impact strength appears independent of composition in the studied size range.

Abstract

We performed a wide-field survey observation of small asteroids using the Hyper Suprime-Cam installed on the 8.2 m Subaru Telescope. We detected more than 3,000 main-belt asteroids with a detection limit of 24.2 mag in the r-band, which were classified into two groups (bluish C-like and reddish S-like) by the g-r color of each asteroid and obtained size distributions of each group. We found that the shapes of size distributions of asteroids with the C-like and S-like colors agree with each other in the size range of 0.4-5 km in diameter. Assuming the asteroid population in this size range is under collision equilibrium, our results indicate that compositional difference hardly affects the size dependence of impact strength, at least for the size range between several hundred meters and several kilometers. This size range corresponds to the size range of ``spin-barrier'', an upper limit observed in the rotation rate distribution. Our results are consistent with the view that most asteroids in this size range have a rubble-pile structure.