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K Atobe, S Ida (Department of Earth and Planetary Sciences, Faculty of Science, Tokyo Institute of technology)
We have investigated the evolution of the obliquity of the hypothetical terrestrial planets due to the tidal interaction with their satellites.
Planetary satellites play important roles for the motion of the spin axis of the planets. The satellite gains the orbital angular momentum through the tidal interaction with the planet, so that it recedes from the planet. On the other hand, the planet loses its spin angular momentum changing its obliquity. It is shown that the Earth's obliquity has been increasing through the tidal interaction with the Moon (e.g., Goldreich 1966, Touma & Wisdom 1994). In addition, the Earth has avoided being in the spin-orbit resonance which induces large-amplitude fluctuations in obliquity because the spin precession is accelerated by the Moon (e.g., Laskar et al. 1993). Since tidal evolution strongly depends on the mass of the satellite, there would be the different evolution of the obliquity from the Earth-Moon system in the extrasolar planet-satellite systems.
In this study, we have numerically simulated the evolution of the satellite's orbit, rotation frequency and obliquity of the planet due to the tidal interaction for various initial conditions. When the rotation frequency of the planet is much larger than the mean motion of the satellite, the obliquity increases. However, when the rotation frequency is smaller than twice of the mean motion of the satellite, the obliquity decreases and becomes 0 degree at the co-rotation point with the satellite. This trend is consistent with the results of Correia et al.(2003). The evolution timescale strongly depends on the mass of the satellite. We will show the detail of our calculations and analytical consideration the behavior of the planetary obliquity.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.