Surveys have revealed many multi-planet systems containing super-Earths and Neptunes in orbits of a few days to a few months. There is debate whether in situ assembly or inward migration is the dominant mechanism of the formation of such planetary systems. Simulations suggest that migration creates tightly packed systems with planets whose orbital periods may be expressed as ratios of small integers (resonances), often in a many-planet series (chain). In the hundreds of multi-planet systems of sub-Neptunes, more planet pairs are observed near resonances than would generally be expected, but no individual system has hitherto been identified that must have been formed by migration. Proximity to resonance enables the detection of planets perturbing each other. Here we report transit timing variations of the four planets in the Kepler-223 system, model these variations as resonant-angle librations, and compute the long-term stability of the resonant chain. The architecture of Kepler-223 is too finely tuned to have been formed by scattering, and our numerical simulations demonstrate that its properties are natural outcomes of the migration hypothesis. Similar systems could be destabilized by any of several mechanisms, contributing to the observed orbital-period distribution, where many planets are not in resonances. Planetesimal interactions in particular are thought to be responsible for establishing the current orbits of the four giant planets in the Solar System by disrupting a theoretical initial resonant chain similar to that observed in Kepler-223.
Architectures of planetary systems and implications for their formation.Proc Natl Acad Sci U S A. 2014 Sep 2;111(35):12616-21. doi: 10.1073/pnas.1304219111. Epub 2014 Apr 28. Proc Natl Acad Sci U S A. 2014. PMID: 24778212 Free PMC article.
A closely packed system of low-mass, low-density planets transiting Kepler-11.Nature. 2011 Feb 3;470(7332):53-8. doi: 10.1038/nature09760. Nature. 2011. PMID: 21293371
Exoplanet orbital eccentricities derived from LAMOST-Kepler analysis.Proc Natl Acad Sci U S A. 2016 Oct 11;113(41):11431-11435. doi: 10.1073/pnas.1604692113. Epub 2016 Sep 26. Proc Natl Acad Sci U S A. 2016. PMID: 27671635 Free PMC article.
M stars as targets for terrestrial exoplanet searches and biosignature detection.Astrobiology. 2007 Feb;7(1):85-166. doi: 10.1089/ast.2006.0125. Astrobiology. 2007. PMID: 17407405 Review.
Observed properties of extrasolar planets.Science. 2013 May 3;340(6132):572-6. doi: 10.1126/science.1233545. Science. 2013. PMID: 23641110 Review.
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Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1.Nature. 2017 Feb 22;542(7642):456-460. doi: 10.1038/nature21360. Nature. 2017. PMID: 28230125 Free PMC article.