Editing Planetary system (section)

====Orbital dynamics====
Planetary systems can be categorized according to their orbital dynamics as resonant, non-resonant-interacting, hierarchical, or some combination of these. In resonant systems the orbital periods of the planets are in integer ratios. The [[Kepler-223]] system contains four planets in an 8:6:4:3 [[orbital resonance]].<ref>{{cite web|last=Emspak|first=Jesse|title=Kepler Finds Bizarre Systems|url=http://www.ibtimes.com/articles/117984/20110302/kepler-finds-strange-worlds-fastest-planet.htm|work=International Business Times|date=March 2, 2011|publisher=International Business Times Inc.|access-date=March 2, 2011}}</ref>
Giant planets are found in mean-motion resonances more often than smaller planets.<ref>{{cite journal | arxiv=1410.4199 | doi=10.1146/annurev-astro-082214-122246 | title=The Occurrence and Architecture of Exoplanetary Systems | year=2015 | last1=Winn | first1=Joshua N. | last2=Fabrycky | first2=Daniel C. | journal=Annual Review of Astronomy and Astrophysics | volume=53 | pages=409–447 | bibcode=2015ARA&A..53..409W | s2cid=6867394 }}</ref>
In interacting systems the planets' orbits are close enough together that they perturb the orbital parameters. The Solar System could be described as weakly interacting. In strongly interacting systems [[Kepler's laws]] do not hold.<ref>{{cite arXiv |eprint=1006.3834 |last1=Fabrycky |first1=Daniel C. |title=Non-Keplerian Dynamics |class=astro-ph.EP |date=2010}}</ref>
In hierarchical systems the planets are arranged so that the system can be gravitationally considered as a nested system of two-bodies, e.g. in a star with a close-in hot Jupiter with another gas giant much further out, the star and hot Jupiter form a pair that appears as a single object to another planet that is far enough out.

Other, as yet unobserved, orbital possibilities include: [[double planet]]s; various [[co-orbital configuration|co-orbital planets]] such as quasi-satellites, trojans and exchange orbits; and interlocking orbits maintained by [[nodal precession|precessing orbital planes]].<ref>{{cite journal | arxiv=0812.2949 | doi=10.1111/j.1365-2966.2009.14552.x | title=Equilibria in the secular, non-co-planar two-planet problem | year=2009 | last1=Migaszewski | first1=Cezary | last2=Goździewski | first2=Krzysztof | journal=Monthly Notices of the Royal Astronomical Society | volume=395 | issue=4 | pages=1777–1794 | doi-access=free | bibcode=2009MNRAS.395.1777M | s2cid=14922361 }}</ref>