Retrograde and prograde motion days. Venus probably began with a fast prograde rotation with a period of several hours much like most of the planets in the Solar System. Venus is close enough to the Sun to experience significant gravitational tidal dissipation, and also has a thick enough atmosphere to create thermally driven atmospheric tides that create a retrograde torque. Venus' present slow retrograde rotation is in equilibrium balance between gravitational tides trying to tidally lock Venus to the Sun and atmospheric tides trying to spin Venus in a retrograde direction. In addition to maintaining this present day equilibrium, tides are also sufficient to
Exoplanetology cases the orientation of the star's rotational axis is unknown. The "Kepler" spacecraft has found a few hundred multi-planet systems and in most of these systems the planets all orbit in nearly the same plane, much like the Solar System. However, a combination of astrometric and radial-velocity measurements has shown that some planetary systems contain planets whose orbital planes are significantly tilted relative to each other. More than half of hot Jupiters have orbital planes substantially misaligned with their parent star's rotation. A substantial fraction of hot-Jupiters even have retrograde orbits, meaning that they orbit in the opposite direction from