Mathematics – Probability
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.2708c&link_type=abstract
American Astronomical Society, DPS meeting #40, #27.08; Bulletin of the American Astronomical Society, Vol. 40, p.435
Mathematics
Probability
Scientific paper
We report on the results of a comprehensive analysis of transverse nongravitational accelerations among the NEA population. The approach is to estimate the best-fitting transverse acceleration on the asteroid, from which the orbit-averaged semimajor axis drift rate can be computed, along with its uncertainty. The signal-to-noise ratio (SNR) is the quotient of the uncertainty and the drift rate. The drift rate is interpreted as arising from the Yarkovsky effect, where positive drift rates indicate direct rotation and negative drifts correspond to retrograde rotators.
From the 90 NEAs that reveal low drift rate uncertainties (<10; x 10-4 AU/Myr), about half show correspondingly low signal (SNR<2), and among these noise-dominated cases the drift rates are evenly divided between inwards and outwards drift. It assumed that these cases are generally reflective of objects with mid-range obliquities. The other half of these objects have a more significant Yarkovsky signal (SNR>2), and among these objects 80% indicate retrograde rotation.
This 4:1 ratio of retrograde to direct rotation is fully consistent with the mechanism proposed by La Spina et al. (2002), where it is assumed that all objects entering the inner solar system through the nu6 resonance do so with retrograde rotation, while the other source regions provide an even distribution of direct and retrograde rotators. Using the techniques of Bottke et al. (2001) the nu6 probability for the individual cases at hand is 55% in the mean, which yields a prediction that 78% are retrograde, in very good agreement with the 80% obtained by direct estimation of semimajor axis drift.
The implication of this result is that NEAs retain some memory of the orbital obliquity with which they left the main belt, and that YORP precession on NEAs does not lead to significant diffusion across the retrograde-prograde boundary.
Bottke William F.
Chesley Steven R.
Vokrouhlicky David
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