The Origin of Venus's Retrograde Rotation: A Collisional Hypothesis

[ion]

A simple question,but to which I can't find a ready answer.

What is the nature of this rotational force that affects all celestial bodies? What was the initial impetus? How does physics explain it?

Thank you,
ion

 

[mathman]

I think you should try to clarify the term "rotational force". However rotations and revolutions of celestial bodies are in general a combination of inertia and gravity. In some extreme cases (e.g. our moon), the rotation and revolution periods are locked, so we always see the same face.

 

[Silvershadow]

I know what you mean, I've been trying to figure this out as well.

I've come across this site which details the rotation time of each planet on it's axis plus the revolution time around the sun. The revolution time of each planet is as expects ie it increases the closer a planet is to the sun. Check this site out for exact figures
http://www.marsdenshs.qld.edu.au/subjects/science/junior_science/astro/solar.html

Also another thread that might interest you is
[URL]https://www.physicsforums.com/archive/topic/1689-1.html

Hopefully someone might be able to give us a full explanation. At best I would guess a planets rotation was initiated/set by the rate of impacts on the planets surface during the creation of our solar system.

Silvershadow

 

[Adrian Baker]

Originally posted by Silvershadow
I know what you mean, I've been trying to figure this out as well.

... At best I would guess a planets rotation was initiated/set by the rate of impacts on the planets surface during the creation of our solar system.

Silvershadow

The above is very true. Many people's idea of the formation of the solar system is of 9 planets forming simply from a cloud of swirling gas orbiting the Sun. However, the system was much more dynamic than this, with proto planets colliding, enormous collisions with other large masses etc. The rotational period of a planet reflects their development history, as well as, in the case of the Earth, the effect the moon has slowing us down.
Venus was tipped almost upside down in its early history and spins very slowly the opposite way to all the other planets! Uranus is on its side too, due to collisions.

 

[Silvershadow]

Venus was tipped almost upside down in its early history and spins very slowly the opposite way to all the other planets! Uranus is on its side too, due to collisions

Just out of interest how do astronomers know what the original axis of the planet was?

Silvershadow

 

[Adrian Baker]

Conservation of angular momentum. As the initial gas and dust cloud collapsed, it would have spun faster and faster, in one direction determined by any tiny initial angular momentum. (like an ice skater pulling in her arms)

Venus, or any other planet for that matter, formed by gravitational attraction of particles, in this collapsing swirling mass. It is not possible, for it to have formed from matter with a different orientation of angular momentum than the rest of the Solar system. Hence, it must have been tipped upside down by a huge collision to account for it spinning on it's axis in a different direction to all the other planets.