  We have investigated the obliquity evolution of terrestrial planets in
habitable zones (at ~ 1AU) in extrasolar planetary systems, due to tidal
interactions with their satellite and host star with wide varieties of
satellite-to-planet mass ratio and initial obliquity, through numerical
calculations and analytical arguments. The obliquity, the angle between
planetary spin axis and its orbit normal, of a terrestrial planet is one of the
key factors in determining the planetary surface environments. A recent
scenario of terrestrial planet accretion implies that giant impacts of
Mars-sized bodies determine the planetary spin and form satellites. With
isotropic giant impacts, tilted spins are more likely to be produced than
straight ones and satellites with various mass are formed. However, most of
previous studies have focused on a particular case of the Earth-Moon systems or
the two-body planar problem. We numerically integrated the evolution of
planetary spin and a satellite orbit with various satellite mass and initial
obliquity. We found that in the case of initially tiled spins, the satellite's
orbit migrates outward until the orbit reaches the critical radius ~ 10-20
planetary radii, but then the migration is reversed to inward one with
large-amplitude oscillation. The satellite eventually falls onto the planetary
surface or it is captured at the synchronous state at several planetary radii.
With the results of numerical integration and analytical arguments, we
identified the parameter regions of qualitatively different evolution.
