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Title:
The Shape and Spin of 101955 (1999 RQ36) from Arecibo and Goldstone Radar Imaging
Authors:
Nolan, Michael C.; Magri, C.; Ostro, S. J.; Benner, L. A.; Giorgini, J. D.; Howell, E. S.; Hudson, R. S.
Affiliation:
AA(Arecibo Obs), AB(U. Maine, Farmington), AC(JPL/Caltech), AD(JPL/Caltech), AE(JPL/Caltech), AF(Arecibo Obs), AG(Washington State U.)
Publication:
American Astronomical Society, DPS meeting #39, #13.06; Bulletin of the American Astronomical Society, Vol. 39, p.433
Publication Date:
10/2007
Origin:
AAS
Bibliographic Code:
2007DPS....39.1306N

Abstract

Near-Earth asteroid 101955 (1999 RQ36) made a close approach to Earth in 1999 and 2005, and was well observed optically and with the Arecibo and Goldstone planetary radar systems. The Arecibo radar observations in 2005 were designed to measure its oblateness, and thus have unusually good aspect coverage, allowing for a good pole determination. Radar images at 19-m and 15-m resolution in 1999 and 7.5-m resolution in 2005 show that RQ36 is well approximated as an irregular spheroid about 580m in diameter. There is no evidence in the radar images for a satellite larger than 15m. The nearly spheroidal shape suggests that it is a strengthless rubble pile, and may have formed by mechanisms similar to near-Earth binary systems, and may even have been in a binary system in its past. Its spin rate of 4.288 hours [Hergenrother pers. comm. 2007] (the 2.1 hour harmonic is ruled out by the radar data) suggests that it has not been spun up by tidal or radiation forces. However, one of the two pole solutions is near ecliptic (lat., lon.) of (-85, 30), which is the YORP spin-up Slivan state [Vokrouhlický et al., 2003].

1999 RQ36 may be one of the older near-Earth spheroidal asteroids, in contrast with 2006 VV2, which is likely a very young one (see presentation by Benner et al.). Older in this context means time since the most recent spinup event.

Reference:

Vokrouhlický, David, David Nesvorný and William F. Bottke, "The Vector Alignments of Asteroid Spins by Thermal Torques,” Nature 425, 147-151 (2003)

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