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Author Topic: Why are there no planets rotating perpendicular to Earth's axis?  (Read 3996 times)

Offline usererror

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Stephen Sommerhalter  asked the Naked Scientists:
   
Why is it that in our solar system there's no planet with an axis of rotation that is perpendicular to Earth's?

I can roughly imagine how the rotation of the Sun's gravitational field causes all the planets to revolve around the sun in the same direction, and how it also causes each planet to rotate on its axis in the same direction as all the other planets.

But, I can not figure out why those explanations rule out having one planet tumble like a barrel even though all the others are spinning like tops,.

Thanks.

What do you think?


 

Offline Ophiolite

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Stephen Sommerhalter  asked the Naked Scientists:
   
Why is it that in our solar system there's no planet with an axis of rotation that is perpendicular to Earth's?
There is. Uranus does exactly this.

The planets coalesced from material in an accretion disc that formed around the protosun. The disc inherited its angular momentum from the collapsing dust cloud that formed the protosun. As a consequence everything was rotating in roughly the same direction. Uranus's odd behaviour is likely due to a colision with another substantial planet during the formative years of the solar system.
 

Offline usererror

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thanks.  I will spend the rest of today trying to imagine what Uranian seasons are like.     
 

Offline chris

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Thanks ophiolite for that helpful answer. I think some people have questioned the collision theory as the reason for Uranus's strange rotation on the grounds that there should be other evidence to support this - eg other vestiges of the impact and so on.

Instead some have suggested that resonances set up between the giant planets during the formation of the solar system might account for this, although, having just checked the reference I had in mind (Brunini et al., Nature, 2006), it seems that they've retracted it:

http://www.ncbi.nlm.nih.gov/pubmed/16641989?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DiscoveryPanel.Pubmed_RVAbstractPlus

Poking about it seems that other authors found fault with the mathematical argument they had put forward.

Nevertheless, it is possible that a variant of this alternative explanation could account for the obliquity of the rotation of some of the planets, including Uranus.

Chris
 

Offline Krupin

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The rotation of Uranus is not so surprising, as the rotation of Jupiter. Only Jupiter's rotation axis nearly perpendicular to its orbital plane. And - strange coincidence - Jupiter, the largest planet.
 

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