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Radiation Recoil Effects on the Dynamical Evolution of Asteroids

Cotto-Figueroa, Desireé

Abstract Details

2013, Doctor of Philosophy (PhD), Ohio University, Physics and Astronomy (Arts and Sciences).
The Yarkovsky effect is a radiation recoil force that results in a semimajor axis drift in the orbit that can cause Main Belt asteroids to be delivered to powerful resonances from which they could be transported to Earth-crossing orbits. This force depends on the spin state of the object, which is modified by the YORP effect, a variation of the Yarkovsky effect that results in a torque that changes the spin rate and the obliquity. Extensive analyses of the basic behavior of the YORP effect have been previously conducted in the context of the classical spin state evolution of rigid bodies (YORP cycle). However, the YORP effect has an extreme sensitivity to the topography of the asteroids and a minor change in the shape of an aggregate asteroid can stochastically change the YORP torques. Here we present the results of the first simulations that self-consistently model the YORP effect on the spin states of dynamically evolving aggregates. For these simulations we have developed several algorithms and combined them with two codes, TACO and pkdgrav. TACO is a thermophysical asteroid code that models the surface of an asteroid using a triangular facet representation and which can compute the YORP torques. The code pkdgrav is a cosmological N-body tree code modified to simulate the dynamical evolution of asteroids represented as aggregates of spheres using gravity and collisions. The continuous changes in the shape of an aggregate result in a different evolution of the YORP torques and therefore aggregates do not evolve through the YORP cycle as a rigid body would. Instead of having a spin evolution ruled by long periods of rotational acceleration and deceleration as predicted by the classical YORP cycle, the YORP effect is self-limiting and stochastic on aggregate asteroids. We provide a statistical description of the spin state evolution which lays out the foundation for new simulations of a coupled Yarkovsky/YORP evolution. Both self-limiting YORP and to a lesser degree a stochastic YORP provide a viable means to explain why the Near-Earth Asteroid (NEA) population seems to remember their initial spin states at the time of delivery from the Main Belt. The YORP effect drives the obliquity of most objects that follow the YORP cycle to the values of 0, 90 and 180 degrees. NEAs could complete a YORP cycle on timescales much shorter than their typical dynamical lifetime. Therefore, one should expect the obliquity distribution of the population of NEAs to be concentrated about those values if they follow the YORP cycle. But to obtain a direct measurement of the obliquity distribution will require radar observations or multiple lightcurves at different illumination and orbital phases for each NEA. Instead of obtaining a direct measurement, the obliquity distribution can be inferred if the distribution of semimajor axis drift rates due to the Yarkovsky effect can be measured. From the linear heat diffusion theory for a spherical body, the semimajor axis drift rate varies linearly with cosine obliquity. Previous studies have attempted to infer the obliquity distribution taking advantage of this simple dependence. However, those results should be considered only approximate because of the neglect of the dependence of the semimajor axis drift rate on density, thermal properties, and shape. Here we seek to obtain the obliquity distribution of NEAs using a better approach based on Bayesian inference that takes into account our prior knowledge of the distributions of the physical parameters on which the semimajor axis drift rates depend. A preliminary obliquity distribution of the NEA population has been estimated to be a V-shaped model that lacks a concentration of objects at an obliquity of 90 degrees and which suggests that the most probable value of the fraction of retrograde rotators is 70.0%. Once the obliquity distribution is obtained, it can in turn be used to test YORP predictions and constrain YORP evolution.
Thomas S. Statler, Ph.D. (Advisor)
Joseph C. Shields, Ph.D. (Committee Member)
Markus Boettcher, Ph.D. (Committee Member)
Keith Milam, Ph.D. (Committee Member)
112 p.

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Citations

  • Cotto-Figueroa, D. (2013). Radiation Recoil Effects on the Dynamical Evolution of Asteroids [Doctoral dissertation, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1380464245

    APA Style (7th edition)

  • Cotto-Figueroa, Desireé. Radiation Recoil Effects on the Dynamical Evolution of Asteroids. 2013. Ohio University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1380464245.

    MLA Style (8th edition)

  • Cotto-Figueroa, Desireé. "Radiation Recoil Effects on the Dynamical Evolution of Asteroids." Doctoral dissertation, Ohio University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1380464245

    Chicago Manual of Style (17th edition)