  In planetary systems with sufficiently small inter-planet spacing, close
encounters can lead to planetary collisions/mergers or ejections. We study the
spin property of the merger products of two giant planets in a statistical
manner using numerical simulations and analytical modeling. Planetary
collisions lead to rapidly rotating objects and a broad range of obliquities.
We find that, under typical conditions for two-planet scatterings, the
distributions of spin magnitude $S$ and obliquity $\Theta_{\rm SL}$ of the
merger products have simple analytical forms: $f_{S} \propto S$ and
$f_{\cos\Theta_{\rm SL}} \propto (1-\cos^2\Theta_{\rm SL})^{-1/2}$. Though
parameter studies, we determine the regime of validity for the analytical
distributions of spin and obliquity. Since planetary mergers is a major outcome
of planet-planet scatterings, observational search for the spin/obliquity
signatures of exoplanets would provide important constraints on the dynamical
history of planetary systems.
