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

TL;DR

This paper presents photometric evidence that a 2.3 km asteroid exceeds the typical spin barrier, suggesting it has significant internal cohesion similar to lunar regolith, challenging the idea that large asteroids are only rubble piles bound by gravity.

Contribution

It introduces the first detailed case of a large asteroid exceeding the spin barrier, proposing lunar-like cohesion as a key factor in its structural integrity.

Findings

(60716) 2000 GD65 rotates faster than 2 hours.

Lunar-like cohesion can prevent disruption of large asteroids.

Most asteroids likely have less cohesion than lunar regolith.

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 +0.6-0.7 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.