Presentation #204.03 in the session Near-Earth Objects: From Asteroids to Meteoroids.
The spin axes and spin rates of near-Earth objects (NEOs) evolve under the influence of gravitational and thermal torques. The Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect tends to drive the obliquities of asteroids to 0 or 180 degrees and speeds up or down their spin rates. However, the orbital plane of asteroids drift because of the gravitational influence of the planets of the solar system and can abruptly change due to close planetary encounters. Therefore, the obliquity, a parameter of the YORP effect, is coupled with the orbital dynamics. On top of this coupling, planetary close encounters can disrupt the spin state of NEOs. In this work we study the spin-orbit problem by modeling together the long-term dynamics of the orbit and YORP while considering the presence of planetary close encounters.
We model the trajectories of NEOs using a semi-analytical propagation tool that combines the two main dynamical effects of secular drift and planetary flybys. First, we use an analytical model of the long-term dynamics as influenced by Jupiter. This leads to a solution of the evolution of the spin state under YORP and the gravitational influence of Jupiter that applies in the absence of planetary close encounters. Then, since we are tracking the trajectory of the asteroid, we detect the close encounters and compute the variation of the orbit elements during close encounters to find their effect on the spin state of the asteroid.
Because of the sensitivity to the initial conditions of the orbits of NEOs, we study the evolution of their orbits and spin states statistically. In this talk we show the results of the study of two types of body, a large asteroid in which the YORP effect plays a small role and the evolution of a small, fast rotator. The semi-analytical propagation allows us to rapidly estimate the trajectories and spin states of individual asteroids, obtaining a statistical representation of their states in the future.