  A new mechanism is proposed to account for the formation of retrograde hot
Jupiter in coplanar star-planet system via close encounter between a Jupiter
mass planet and a brown dwarf mass planet. After long timescale scattering
between several Jupiter mass planets with inner orbits, the remaining planets
still rotating around the star could have large semimajor with large
eccentricity. If there exists a brown dwarf mass planet in distant orbit around
the star, planetary encounter may happen. After encounter, the Jupiter mass
planet may rotate around the star in a retrograde orbit with extremely large
eccentricity and the periastron can reach about 0.01 AU, which means that,
within the first several orbits around the star, tidal interaction from the
star can shrink the semimajor axis of the planet quickly. Thus, the Jupiter
mass planet is isolated from the brown dwarf mass planet due to the quick
decrease of its apastron distance and eventually evolves into a retrograde hot
Jupiter.
