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

• Published in: Icarus (New York, N.Y. 1962) Vol. 267; pp. 243 - 254
• Main Authors: Polishook, D., Moskovitz, N., Binzel, R.P., Burt, B., DeMeo, F.E., Hinkle, M.L., Lockhart, M., Mommert, M., Person, M., Thirouin, A., Thomas, C.A., Trilling, D., Willman, M., Aharonson, O.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 15.03.2016
• Subjects: Asteroids; Asteroids, rotation; Barriers; Belts; Cohesion; Evolution; Gravitation; Photometry; Piles; Rotational dynamics; Rotational dynamics; Asteroids; Photometry; Asteroids, rotation
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2015.12.031

•Asteroid 60716 2000GD65 is a fast rotating (1.9529h) relatively large (2.3km) body.•This limits the density to a higher value than the density of an S-complex body.•This suggests that 60716 has a significant cohesion, similar to weak lunar cohesion.•60716's uniqueness suggests that most asteroids have lower cohesion than the Moon. The rubble pile spin barrier is an upper limit on the rotation rate of asteroids larger than ∼200–300m. Among thousands of asteroids with diameters larger than ∼300m, only a handful of asteroids are known to rotate faster than 2.0h, all are in the sub-km range (⩽0.6km). 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+0.6km, completes one rotation in 1.9529±0.0002h. 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 3.9h 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.