Why does Venus have retrograde rotation?

[Northern_Piper]

Are there any theories to explain its retrograde rotation?

[TheGunIsMightierThanThePen]

Retrograde and prograde motion | Planets

It is unlikely that Venus was formed with its present slow retrograde rotation, which takes 243 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 account for evolution of Venus’s rotation from a primordial fast prograde direction to its present-day slow retrograde rotation.

[penultima_thule]

Some things are unfathomable:

[Chronos]

Surprisingly, Earth also seems to play a part in the tidal effects on Venus: Whenever the two planets are at closest approach, Venus is always showing the same face to us.

[Whack-a-Mole]

How can they tell? All we see is clouds. (I believe you, really asking)

[Northern_Piper]

There have been some orbiters of Venus.

For example, the Pioneer Venus Orbiter had cloud-penetrating radar:

• a surface radar mapper (ORAD) to determine topography and surface characteristics. Observations could only be conducted when the probe was closer than 4700 km over the planet. A 20 watt S-band signal (1.757 gigahertz) was sent to the surface that reflected it, with the probe analyzing the echo. Resolution at periapsis was 23 x 7 km.

It orbited Venus for 14 years.