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The Question
(Submitted October 26, 1998)
Why is the rotation of Venus retrograde, or East to West - unlike nearby
planets?
The Answer
We got two good answers to this question from our distribution of
scientists. Here they are:
"The standard answer to this question and things like Neptune's tilt
is that there was a large collision early in the planetary formation
process. The models of planetary and solar system formation have
the angular momentums of the planets and their orbits in the same
direction as the initial angular momentum of the gas cloud. You need
something like a collision to get anything else."
- Eric Christian
"Of the nine planets, a bare majority (Earth, Mars, Jupiter, Saturn, and
Neptune) rotate in a way we consider 'normal'. Mercury and Venus are
slow, Venus, Uranus, and Pluto are retrograde, Uranus and Pluto are highly
inclined. Mars' inclination varies chaotically over long (billion-year)
time scales, so it is not always 'normal' either. It is only parochialism
that makes us point and laugh at the zany antics of the other planets.
"How a planet rotates is related to how it was formed from the accretion
of planetesimals. If more impacts occur on one side than the other, then
it will tend to rotate accordingly. But the impacts are largely random.
Tidal effects can also change the rotation."
-David Palmer
Hope this helps to answer your question!
Maggie Masetti & Koji Mukai
for Ask A High-Energy Astronomer
Questions on this topic are no longer responded to by the "Ask a
High-Energy Astronomer" service. See http://imagine.gsfc.nasa.gov/docs/ask_astro/ask_an_astronomer.html
for help on other astronomy Q&A services.
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