Physics – Geophysics
Scientific paper
Sep 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.5609m&link_type=abstract
American Astronomical Society, DPS meeting #41, #56.09
Physics
Geophysics
Scientific paper
We present an accurate secular theory of the effects of Binary YORP (BYORP) and discuss its implications. The theory represents the solar radiation pressure force, which is responsible for the BYORP effect, as a Fourier series based on the physical properties of the secondary body in a binary asteroid system. The theory averages over the binary orbit and over the heliocentric orbit separately. The theory predicts that the orbit expansion rate is independent of the asteroid's thermal inertia for a near circular orbit, although the evolution of the angular momentum and eccentricity vectors do depend on the thermal inertia. This is similar to the results found for YORP where the spin rate evolution is independent of thermal inertia, but the spin axis orientation evolution is not.
The predicted secular rates from the theory can be used to make long term predictions of a binary asteroid system's complete orbital evolution. We have applied the theory to the binary asteroid 1999 KW4 for which we have accurate models. We compute the current growth rate of the semi-major axis to be 5.4 cm/year. The full secular theory was integrated forwards and backwards in time and predicts that the orbit will double in size in roughly 14,000 years and was half of it's current size approximately 20,000 years ago. Assuming that BYORP is active for this system, these results indicates a relatively recent formation for this object. The orbit will expand beyond the Hill sphere roughly 36,000 years from now, yielding a fairly short lifetime. These calculations have not incorporated solar tidal forces, but will in the future. Results of the full orbit evolution for 1999 KW4 and their implications will be presented at the meeting.
This work was supported by a grant from NASA's Planetary Geology and Geophysics Program.
McMahon J. J.
Scheeres Dan
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