Sphericity Preference in Shapes of Sub-km-Sized Fast-Rotating Main-Belt Asteroids

Details Sphericity Preference in Shapes of Sub-km-Sized Fast-Rotating Main-Belt Asteroids Sphericity Preference in Shapes of Sub-km-Sized Fast-Rotating Main-Belt Asteroids

Mar 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011pasj...63s.577n&link_type=abstract

Publications of the Astronomical Society of Japan, Vol.63, No.SP2, pp.577--584

Astronomy and Astrophysics

Astronomy

1

Minor Planets, Asteroids, Solar System: Light Curves, Solar System: Rotation

Scientific paper

Here, we report on results of statistical analyses on spin periods and shapes of main-belt asteroids (MBAs) smaller than ˜1 km in diameter, which were derived from lightcurve observations of a single night with the 8.2 m Subaru telescope. It is shown that, among our detected 68 MBAs giving reliable lightcurve periods, the fraction of fast-rotating asteroids (with spin periods of <˜2.3 hr, candidates of monolithic bodies) is about 49%. In particular, statistical tests reveal with a high confidence level that, in terms of the shape (deduced from the light variation amplitude), the fast rotators belong to a population quite different from that for non fast-rotators; in other words, most of the fast-rotators show a strong trend that they are more spherical in shape than the non fast-rotator group. Consideration of several orbital and rotational evolution timescales for small asteroids in the main asteroid belt seems to indicate that the above-mentioned trend is not by coincidence, but primordial. Therefore, referring to the shape distributions of impact fragments produced in laboratory experiments, our discovered sphericity preference of small fast-rotating asteroids probably requires some spin deceleration mechanisms, which selectively worked on all elongated objects during their impact formation and/or subsequent evolution. We also note that our fast rotators are much more spherical compared to known small MBAs and near-Earth objects.

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