A 2 km-size asteroid challenging the rubble-pile spin barrier – A case for cohesion

Abstract The rubble pile spin barrier is an upper limit on the rotation rate of asteroids larger than ∼200–300 m. Among thousands of asteroids with diameters larger than ∼300 m, only a handful of asteroids are known to rotate faster than 2.0 h, all are in the sub-km range (⩽0.6 km). Here we present photometric measurements suggesting that (60716) 2000 GD65 , an S-complex, inner-main belt asteroid with a relatively large diameter of 2.3 - 0.7 + 0.6 km , completes one rotation in 1.9529 ± 0.0002 h . Its unique diameter and rotation period allow us to examine scenarios about asteroid internal structure and evolution: a rubble pile bound only by gravity; a rubble-pile with strong cohesion; a monolithic structure; an asteroid experiencing mass shedding; an asteroid experiencing YORP spin-up/down; and an asteroid with a unique octahedron shape results with a four-peak lightcurve and a 3.9 h period. We find that the most likely scenario includes a lunar-like cohesion that can prevent (60716) 2000 GD65 from disrupting without requiring a monolithic structure or a unique shape. Due to the uniqueness of (60716) 2000 GD65 , we suggest that most asteroids typically have smaller cohesion than that of lunar regolith.