"Jonathan Silverlight" wrote in message
...
I think that Mars and Venus are part of the evidence for the theory
being correct! The axis of Mars is supposed to have varied between near
zero and fifty degrees, though I can't remember if this is just theory
or there is some evidence for it, and Venus can be thought of as "upside
down" - it's rotating very slowly "the wrong way" compared to the other
planets, so its inclination is usually expressed as 177 degrees, not 3.

If I remember right (and my astronomy days are way behind me), Venus' "day"
is very long, damn close to its year. In that case, it would be more likely
that Venus is becoming tidally locked, and is "rocking" back and forth prior
to settling in with one face permanently to the sun, and less likely that it
"flipped" by almost 180 degrees.

As to Mars, well, geologists have tracked Earth's historical magnetic pole
movements by examining volcanic rock. All I've ever seen stated about the
polar axis is a precession with a period of 23,600 years or thereabouts.
Seems unlikely that they'd know more about Martian axis movements that
Earth's. I'd kind of like to know how they back up their estimates of that
Martian variation-- as far as I know, we haven't planted a geologist on Mars
yet (would that be an Areologist?)