Uranus's Tilt: Not caused by an impact?

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Uranus's Tilt: Not caused by an impact?

Post by Sirius_Alpha on 1st December 2009, 10:10 pm

A collisionless scenario for Uranus tilting
http://arxiv.org/abs/0912.0181

Abstract wrote:The origin of the high inclination of Uranus' spin-axis (Uranus' obliquity) is one of the great unanswered questions about the Solar system. Giant planets are believed to form with nearly zero obliquity, and it has been shown that the present behaviour of Uranus' spin is essentially stable. Several attempts were made in order to solve this problem. Here we report numerical simulations showing that Uranus' axis can be tilted during the planetary migration, without the need of a giant impact, provided that the planet had an additional satellite and a temporary large inclination. This might have happened during the giant planet instability phase described in the Nice model. In our scenario, the satellite is ejected after the tilt by a close encounter at the end of the migration. This model can both explain Uranus' large obliquity and bring new constraints on the planet orbital evolution.

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Re: Uranus's Tilt: Not caused by an impact?

Post by Stalker on 2nd December 2009, 2:03 am

Maybe the hypothetical satellite was the Lykawka's Aernus?
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Re: Uranus's Tilt: Not caused by an impact?

Post by Sirius_Alpha on 2nd December 2009, 2:08 am

The satellite they speak of, as described in the paper, has a mass of 0.01 Uranus-masses. Significantly less than what one would expect from an Earth-radius planet, and even still, larger than what planet-formation models would predict. So even if Aernus exists, it probably isn't this hypothetical moon.

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Re: Uranus's Tilt: Not caused by an impact?

Post by Lazarus on 3rd December 2009, 5:05 pm

Interesting that the postulated satellite would be too large according to current theories of the formation of gas giant satellite systems. A satellite of this mass ratio around a Saturn-like planet (thought to be best for exomoon detection because of the low density) would have a mass roughly the same as that of Earth.
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Re: Uranus's Tilt: Not caused by an impact?

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