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The Gyro-Gravitational Spin Vector Torque Dynamics of Main Belt Asteroids in relationship with their Tilt and their Orbital Inclination

Thierry De Mees
Year: 2007 Pages: 17
Keywords: Main Belt Asteroids, gravitation, gyrotation, prograde, retrograde, orbit, asteroid precession, asteroid nutation, asteroid tilt, angular momentum
Several observational studies of the main belt asteroids showed a direct link between the evolution of the spin vectors and the inclination of their orbit. A study wherein the evolution of 25 main belt asteroids and 125 synthetic objects was computed over 1Myr (E. Skogl?v, A. Erikson, 2002) clearly quantified this link. Verification of these results with the observation of 73 asteroids confirmed the results. Non-gravitational (YORP-/Yarkovsky-) torques are not considered here. Following observational conclusions have been made by E. Skogl?v and A. Erikson:
  • the spin oscillations' amplitude increases with increasing orbital inclination of the asteroid.
  • the largest spin oscillations' amplitudes are found if the initial spin vector lays in the orbital plane.
  • the spin obliquity differences are generally insensitive to the shape, composition and spin rate of the asteroids.
  • there is a significant majority of asteroids with a prograde spin vector compared to retrograde ones.
  • the spin vectors of prograde asteroids are more chaotic than the spin vectors of retrograde asteroids.
  • there are very few asteroids having a spin vector that lays in the vicinity of the orbital plane.
  • the heliocentric distance is relevant for the spin vector behaviour.

In this paper it was found that the gyro-gravitation theory, which is the closest Euclid theory to the General Relativity Theory of Einstein, complies very well with these observations. We find that the asteroid's tilt varies continuously and tends to reach more or less a retrograde spin in relation to the Sun's spin. The tilt varies however spiral-wise due to the gyroscopic effect that causes a motion of precession as well.