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
Upsilon Andromedae from the star. Both of these planets are in more eccentric orbits than any of the planets in the Solar System (including Pluto). Upsilon Andromedae d resides in the system's habitable zone. The orbital parameters of this three planet system have been fully determined. The system is not coplanar, with each other or with the stellar rotation, as in our solar system. Simulations shows that the measured configuration of the planets produces indeed stable orbits for at least 100 million years, where planets "b" and "d" remain roughly coplanar. General relativity is expected to have strong effects on planet "b",