Evolution of NEO rotation rates due to close encounters with Earth and Venus

In this paper we study the statistical effect of planetary flybys on the rotation rates and states of Near Earth Objects (NEOs). Our approach combines numerical and analytical methods within a Monte Carlo model that simulates the evolution of the NEO spin rates. We take as input for the simulation a source distribution of spin states and evolve it to find their steady state distribution. In performing this evolution we track the changes in the spin rate and state distribution for the different components of the NEO population. We show that the cumulative effect of planetary encounters is to spin up the overall population of NEOs. This spin up effect holds on average only, and particular members of the population may experience an overall decrease in rotation rate. This effect is clearly seen across all components of the NEO population and is significant both statistically and physically. For initially slow rotators the spin up effect is strong, lowering the mean rotation period by 32%. For faster rotating populations the effect is less, lowering the spin period by 15% for the intermediate case, 6% for fast rotating rubble piles, and 8% for fast rotating monoliths. Physically, the spin up effect pushes 1% of the fast rotating rubble-pile NEOs over the disruption limit, while 6% of these bodies experience a sub-disruption event that could modify their physical structure. For monolithic NEOs, the spin up effect is self-limiting, reaching a minimum spin period of 1.1 hr, with a strong cut-off between 2–3 hr. This has two implications. First, it may not be necessary to invoke the rubble-pile hypothesis to recover a cut-off in spin period. Second, it shows that planetary flybys cannot account for the extremely rapid rotation rates of some small NEOs. We also tested a different balance between the effects of Earth and Venus by treating the Aten sub-class of asteroids separately. Due to increased interactions with the planets, the spin up effect is more pronounced (10%) and disruptions increase by a factor of three. The slow rotation tails of the spin distributions are increased to longer periods, in general, with rotation periods of over 100 hr occurring for a few tenths of a percent for some component populations. Thus, this mechanism may account for some of the noted excess in slow rotators among the NEOs. Planetary flybys also cause NEOs to enter a tumbling state, with approximately 0.5% of the population being placed into a long-axis rotation mode. Finally, based on the evolution of spin states of different components of the NEO population, we compared the evolved states with the measured distribution of NEOs to estimate the relative populations of these components that comprise the NEOs.

[1]  D. Scheeres.  Stability of Binary Asteroids , 2001 .

[2]  Robert A Kolvoord,et al.  Collision lifetimes and impact statistics of near-Earth asteroids , 1993 .

[3]  Steven J. Ostro,et al.  Shape and Non-Principal Axis Spin State of Asteroid 4179 Toutatis , 1995, Science.

[4]  S. Ostro,et al.  Effects of Gravitational Interactions on Asteroid Spin States , 2000 .

[5]  R. Binzel,et al.  Origins for the Near-Earth Asteroids , 1992, Science.

[6]  Lance A. M. Benner,et al.  Asteroid Radar Astronomy , 1983 .

[7]  D. Morrison.  The Spaceguard Survey: Report of the NASA International Near-Earth-Object Detection Workshop , 1992 .

[8]  H. Melosh,et al.  Gravitational Aggregates: Evidence and Evolution , 2002 .

[9]  Joseph A. Burns,et al.  Asteroid Nutation Angles , 1973 .

[10]  Keith A. Holsapple,et al.  Equilibrium Configurations of Solid Cohesionless Bodies , 2001 .

[11]  D. Vokrouhlický,et al.  The Effect of Yarkovsky Thermal Forces on the Dynamical Evolution of Asteroids and Meteoroids , 2002 .

[12]  D. Scheeres.  Dynamics about Uniformly Rotating Triaxial Ellipsoids: Applications to Asteroids , 1994 .

[13]  S. Love,et al.  Tidal Distortion and Disruption of Earth-Crossing Asteroids , 1997 .

[14]  P. Geissler,et al.  The Fate of Asteroid Ejecta , 2002 .

[15]  M. Di Martino,et al.  Physical properties of near-Earth asteroids , 1998 .

[16]  Daniel J. Scheeres.  Changes in Rotational Angular Momentum due to Gravitational Interactions between Two Finite Bodies* , 2001 .

[17]  Michael P. Wiper,et al.  Bayesian statistical analysis of asteroid rotation rates , 1999 .

[18]  P. N. Smith,et al.  The Properties of Fragments from Catastrophic Disruption Events , 1998 .

[19]  J. Solem,et al.  Shaping of Earth-Crossing Asteroids by Tidal Forces , 1996 .

[20]  Petr Pravec,et al.  Fast and Slow Rotation of Asteroids , 2000 .

[21]  Brett James Gladman,et al.  The Near-Earth Object Population , 2000 .

[22]  Side effects of collisions: Spin Rate Changes, Tumbling Rotation States, and Binary Asteroids , 2002 .

[23]  On the Slow Rotation of Asteroids , 2002 .

[24]  M. Fulchignoni,et al.  On the evolution of the asteroid spin. , 1995 .

[25]  William F. Bottke,et al.  Formation of asteroid satellites and doublet craters by planetary tidal forces , 1996, Nature.

[26]  Richard P. Binzel,et al.  Asteroid rotation rates - Distributions and statistics , 1989 .

[27]  R. Jedicke,et al.  Debiased Orbital and Absolute Magnitude Distribution of the Near-Earth Objects , 2002 .