Nearly half the exoplanets found within binary star systems reside1 in very wide binaries with average stellar separations greater than 1,000 astronomical units (one astronomical unit (au) being the Earth–Sun distance), yet the influence of such distant binary companions on planetary evolution remains largely unstudied. Unlike their tighter counterparts, the stellar orbits of wide binaries continually change under the influence of the Milky Way’s tidal field and impulses from other passing stars. Here we report numerical simulations demonstrating that the variable nature of wide binary star orbits dramatically reshapes the planetary systems they host, typically billions of years after formation. Contrary to previous understanding2, wide binary companions may often strongly perturb planetary systems, triggering planetary ejections and increasing the orbital eccentricities of surviving planets. Although hitherto not recognized, orbits of giant exoplanets within wide binaries are statistically more eccentric than those around isolated stars. Both eccentricity distributions are well reproduced when we assume that isolated stars and wide binaries host similar planetary systems whose outermost giant planets are scattered beyond about 10 au from their parent stars by early internal instabilities. Consequently, our results suggest that although wide binaries eventually remove the most distant planets from many planetary systems, most isolated giant exoplanet systems harbour additional distant, still undetected planets.
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We thank J. Chambers and R. Roškar for discussions. This work was funded by a CITA National Fellowship and Canada’s NSERC. S.N.R. thanks the PNP programme of CNRS and the NASA Astrobiology Institute’s Virtual Planetary Laboratory team. Our computing was performed on the SciNet General Purpose Cluster at the University of Toronto.
The authors declare no competing financial interests.
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Kaib, N., Raymond, S. & Duncan, M. Planetary system disruption by Galactic perturbations to wide binary stars. Nature 493, 381–384 (2013). https://doi.org/10.1038/nature11780