  The timescales over which the YORP effect alters the rotation period and the
obliquity of a small asteroid can be very different, because the corresponding
torques couple to different aspects of the object's shape. For nearly
axisymmetric, "top-shaped" near-Earth asteroids such as 101955 Bennu, spin
timescales are an order of magnitude or more longer than obliquity timescales,
which are of order 10^5 to 10^6 yr. The observed low obliquities (near 0 or 180
degrees) of top-shaped asteroids do not constitute evidence that they acquired
their present shapes and spins through YORP spin-up, because low obliquities
are expected regardless of the spin-up or reshaping mechanism.
