The Sun’s equator and the planets’ orbital planes are nearly aligned, which is presumably a consequence of their formation from a single spinning gaseous disk. For exoplanetary systems this well-aligned configuration is not guaranteed: dynamical interactions may tilt planetary orbits, or stars may be misaligned with the protoplanetary disk through chaotic accretion1 , magnetic interactions2 or torques from neighbouring stars. Indeed, isolated ‘hot Jupiters’ are often misaligned and even orbiting retrograde3,4. Here we report an analysis of transits of planets over starspots5,6,7 on the Sun-like star Kepler-30 (ref. 8), and show that the orbits of its three planets are aligned with the stellar equator. Furthermore, the orbits are aligned with one another to within a few degrees. This configuration is similar to that of our Solar System, and contrasts with the isolated hot Jupiters. The orderly alignment seen in the Kepler-30 system suggests that high obliquities are confined to systems that experienced disruptive dynamical interactions. Should this be corroborated by observations of other coplanar multi-planet systems, then star–disk misalignments would be ruled out as the explanation for the high obliquities of hot Jupiters, and dynamical interactions would be implicated as the origin of hot Jupiters.
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Kepler was competitively selected as the tenth Discovery mission. Funding for this mission was provided by NASA’s Science Mission Directorate. The data presented in this Letter were obtained from the Mikulski Archive for Space Telescopes (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contracts. S. Albrecht, E. Agol, J. A. Carter, L. Doyle and A. Shporer provided comments on the manuscript. D.C.F. acknowledges NASA support through Hubble Fellowship grant HF-51272.01-A, awarded by STScI. D.R. acknowledges the Harvard Institute for Theory and Computation. E.B.F., M.J.H. and J.N.W. acknowledge NASA support through the Kepler Participating Scientist programme.
The authors declare no competing financial interests.
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Sanchis-Ojeda, R., Fabrycky, D., Winn, J. et al. Alignment of the stellar spin with the orbits of a three-planet system. Nature 487, 449–453 (2012). https://doi.org/10.1038/nature11301
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