Statistics – Computation
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dda....39.0202f&link_type=abstract
American Astronomical Society, DDA meeting #39, #2.02
Statistics
Computation
Scientific paper
We address the effect of continued YORP spin-up on the rapidly rotating primaries of the largest class of binary asteroid systems: asynchronous binaries typified by 1999 KW4. We show that this leads to the continued expansion of these systems on time scales several times faster than tidal dissipation expansion rates, and maintains the primary spin at near-critical rates. We theorize angular acceleration of the primary (due to YORP) recurringly moves it to supercritical spin, causing episodic lofting of primary regolith. Angular momentum thus added to the primary is transferred, through gravitational interaction of lofted particles with both components, into combined orbit and secondary angular momentum, producing orbit expansion. To validate these hypotheses, we first use high-fidelity dynamic simulation of particles in the full gravity field of the components, themselves propagating according to their full-detail mutual gravitation. We find final disposition (return impact, transfer impact, escape) and average particle-mass-specific angular momentum change results for dynamically simulated regolith particles lofting at different initial primary spin rates and relative poses. We use the dynamic simulation output to perform probability-based mapping of many particles on the primary surface forward in time to extreme durations at little computational cost. Tracking changes to mass, inertia dyad, rotation states, and centroid position and velocity for each component, in response to the particle motion, allows changes to the angular momenta of primary, secondary, and mutual orbit to be tracked. This clearly demonstrates the angular momentum transfer mechanism behind binary separation evolution, validating our theory. Given system parameter values for KW4, its current expansion rate is ≈0.861 m/kyr, orbit size doubling and halving times are ≈2.46 Myr and ≈1.70 Myr. Assuming 10 Mt free surface material, on-average mass lofting rate and material mass in flight are ≈0.3 kg/s and kg, though lofting's episodic nature complicates the latter's interpretation.
Fahnestock Eugene G.
Scheeres Daniel J.
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