55 Cnc system: Misalignment with coplanarity?

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55 Cnc system: Misalignment with coplanarity?

Post by Sirius_Alpha on 27th October 2011, 8:25 pm

55 Cancri: A Coplanar Planetary System that is Likely Misaligned with its Star
http://arxiv.org/abs/1110.5911

Although the 55 Cnc system contains multiple, closely packed planets that are presumably in a coplanar configuration, we use numerical simulations to demonstrate that they are likely to be highly inclined to their parent star's spin axis. Due to perturbations from its distant binary companion, this planetary system precesses like a rigid body about its parent star. Consequently, the parent star's spin axis and the planetary orbit normal likely diverged long ago. Because only the projected separation of the binary is known, we study this effect statistically, assuming an isotropic distribution for wide binary orbits. We find that the most likely projected spin-orbit angle is ~50 degrees, with a ~30% chance of a retrograde configuration. Transit observations of the innermost planet - 55 Cnc e - may be used to verify these findings via the Rossiter-McLaughlin effect. 55 Cancri may thus represent a new class of planetary systems with well-ordered, coplanar orbits that are inclined with respect to the stellar equator.

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Re: 55 Cnc system: Misalignment with coplanarity?

Post by Lazarus on 29th October 2011, 2:48 am

That's pretty neat actually, the multi-planet orbits stabilising the system even as it precesses.

Guess this is similar to why there is a regular satellite system around Uranus despite the inclination with respect to the Sun exceeding the Kozai angle.
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Re: 55 Cnc system: Misalignment with coplanarity?

Post by Sirius_Alpha on 29th October 2011, 11:33 am

I didn't think Uranus' satellites precess as a rigid body though, do they? Is that needed for a coplanar system to misalign without scattering?

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Re: 55 Cnc system: Misalignment with coplanarity?

Post by Lazarus on 21st November 2011, 5:13 pm

Another question is whether this would also affect the planets' spin axes. If not, then there could be some substantial obliquity variations going on there.
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