# GJ 876 - Laplace Resonance, Coplanarity, Dynamics

## GJ 876 - Laplace Resonance, Coplanarity, Dynamics

The architecture of the GJ876 planetary system. Masses and orbital coplanarity for planets b and c

http://arxiv.org/abs/0901.3144

http://arxiv.org/abs/0901.3144

Abstract wrote:We present a combined analysis of previously published high-precision radial velocities and astrometry for the GJ876 planetary system using a self-consistent model that accounts for the planet-planet interactions. Assuming the three planets so far identified in the system are coplanar, we find that including the astrometry in the analysis does not result in a best-fit inclination significantly different than that found by Rivera and collaborators from analyzing the radial velocities alone. In this unique case, the planet-planet interactions are of such significance that the radial velocity data set is more sensitive to the inclination of the system through the dependence of the interactions on the true masses of the two gas giant planets in the system (planets b and c). The astrometry does allow determination of the absolute orbital inclination (i.e. distinguishing between i and 180-i) and longitude of the ascending node for planet b, which allows us to quantify the mutual inclination angle between its orbit and planet c's orbit when combined with the dynamical considerations. We find that the planets have a mutual inclination of 5.0 +3.9 -2.3 degrees. This result constitutes the first determination of the degree of coplanarity in an exoplanetary system around a normal star. That we find the two planets' orbits are nearly coplanar, like the orbits of the Solar System planets, indicates that the planets likely formed in a circumstellar disk, and that their subsequent dynamical evolution into a 2:1 mean motion resonance only led to excitation of a small mutual inclination. This investigation demonstrates how the degree of coplanarity for other exoplanetary systems could also be established using data obtained from existing facilities.

Last edited by Sirius_Alpha on 1st May 2015, 9:08 pm; edited 1 time in total

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**Sirius_Alpha**- Admin
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## Re: GJ 876 - Laplace Resonance, Coplanarity, Dynamics

I'd seen an abstract about this on BAAS a while back, but didn't post about it because the talk hadn't happened yet (and the abstract didn't include the result). Good to see more results coming out of studies of Gliese 876, it's a fascinating system... unfortunately getting inclination and longitude of the ascending node for planet d is going to be a lot harder!

(BTW this is an ideal topic for the Mechanics forum)

(BTW this is an ideal topic for the Mechanics forum)

**Lazarus**- dG star
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## Re: GJ 876 - Laplace Resonance, Coplanarity, Dynamics

I've placed it in Planetology because it's a system-specific story.

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## Re: GJ 876 - Laplace Resonance, Coplanarity, Dynamics

Well this doesn't seem to be so much about the intrinsic properties of the planets themselves but the behaviour of the system as a whole, which would fit more with the mechanics side of things, no?

**Lazarus**- dG star
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## Re: GJ 876 - Laplace Resonance, Coplanarity, Dynamics

True, I didn't consider that.

-> Moved.

-> Moved.

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## Re: GJ 876 - Laplace Resonance, Coplanarity, Dynamics

btw if any of you are using Celestia, I have created a .ssc file that will implement the orbits in table 2 of the paper... see here

**Lazarus**- dG star
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## Re: GJ 876 - Laplace Resonance, Coplanarity, Dynamics

I have created a .stc to work with Lazarus' data, showing the RV effects of all three planets on GJ 876. Interesting to visually see the star's RV movements. The effect of GJ 876 d is small, but it can be discerned if you set it to follow the right barycentre.

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## Laplace resonance at Gliese 876

Dynamical analysis of the Gliese-876 Laplace resonance

http://arxiv.org/abs/1305.6768

Published orbital solutions appear to be chaotic but stable for long periods of time. Inclinations of up to ~15 degrees to the other planets are allowed for the outer planet before the system becomes unstable.

http://arxiv.org/abs/1305.6768

Published orbital solutions appear to be chaotic but stable for long periods of time. Inclinations of up to ~15 degrees to the other planets are allowed for the outer planet before the system becomes unstable.

**Lazarus**- dG star
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## Re: GJ 876 - Laplace Resonance, Coplanarity, Dynamics

An Empirically Derived Three-Dimensional Laplace Resonance in the Gliese 876 Planetary System

http://arxiv.org/abs/1504.07995

Pretty well constraints the orbits of the b, c and e planets to coplanar. The d planet is only loosely constrained.

(also, I've merged a couple topics on GJ 876 dynamics and renamed the thread title)

http://arxiv.org/abs/1504.07995

Pretty well constraints the orbits of the b, c and e planets to coplanar. The d planet is only loosely constrained.

(also, I've merged a couple topics on GJ 876 dynamics and renamed the thread title)

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