polar wander

[Ags]

The Moon is supposed to stabilize earth's axis, keeping our seasons stable and making complex life possible. If that is the case, why are almost all the other planets more or less the right way up (Uranus being the exception). No other planet has a satellite as large as the Moon relative to the size of the planet (i.e Jupiter's moons are very large, but they are insignificant relative to their planet), so if I understand it correctly, the other planets' spin is not stabilized by their moons.

In fact, Uranus's axial tilt is usually explained as the result of an impact - I've never seen it explained as polar wander.

[Ags]

Any ideas anyone?

[George Jones]

I do have one book that compares the axis stability of Earth and Mars,

An Introduction to Modern Astrophysics: Amazon.co.uk: Bradley W. Carroll, Dale A. Ostlie: Books

but I don't have it home with me. This book says that when the effects of general relativity are taken into account, simulations indicate that the orientation of Mars's axis is unstable. Maybe on Monday I'll post the relevant passage.

[toml42]

I never quite understood the argument that our seasons are required for complex life and that our axial tilt is 'perfect' for life.

There is very little seasonal change at the equator, and at the poles it is so extreme as to cause months of day/night. yet living things do fine. am i missing something?

[Ags]

I think the argument is not that the seasons themselves are important, but the regularity of the seasons. Obviously penguins have adapted to their frozen environment, but if our axis wobbled and they found themselves at the equator they would not be able to adapt to such a sudden and extreme change. So the argument is it would be hard to evolve complexity or size as this implies specialization which would not be favored by an unstable environment.

On the subject of Mars' unstable axis... I've read that it is unstable too, but Mars has substantial poles with loads of water ice and CO2 ice. If the poles really did wander on Mars, surely there would be characteristic erosion or surface features in the previous locations of the poles? Perhaps if Mars' poles do drift about this causes periods of wet conditions?

[Earl]

I never quite understood the argument that our seasons are required for complex life and that our axial tilt is 'perfect' for life.

There is very little seasonal change at the equator, and at the poles it is so extreme as to cause months of day/night. yet living things do fine. am i missing something?

Its a generalization that the conditions due to our location / tilt allow life forms within a bandwidth of conditions to exist, outside those conditions it cant exist and due to the interrelations in the eco system, narrow that bandwidth and the knock on effects cause mass extinctions..... which could escalate.

[toml42]

I guess it depends on the speed and extremity of any axial wobble. It seems to be true that changes in environment and climate, whilst potentially causing some extinctions, generally drive diversity and evolution by forcing adaption and speciation, rather than maintaining a status quo.

For example; it has been proposed that our ancestors were forced to come down from the trees and walk further and further distances in a savanna setting due to climate change, and intelligence was spurred by the difficulty of adapting to this new existence.

maybe under the right circumstances, a system with a larger degree of polar wander than our own (though not enough so as to be completely destructive) might serve to accelerate the process of the evolution and speciation of complex life, perhaps being more likely to reach intelligence in the process?