The well-aligned orbit of Wasp-84b: evidence for disk migration of a hot Jupiter

D. R. Anderson*, A. H. M. J. Triaud, O. D. Turner, D. J. A. Brown, B. J. M. Clark, B. Smalley, A. Collier Cameron, A. P. Doyle, M. Gillon, C. Hellier, C. Lovis, P. F. L. Maxted, D. Pollacco, D. Queloz, A. M. S. Smith

*Corresponding author for this work

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We report the sky-projected orbital obliquity (spin–orbit angle) of WASP-84 b, a 0.69 planet in an 8.52 day orbit around a G9V/K0V star, to be λ = −0.3 ± 1.7°. We obtain a true obliquity of ψ = 17.3 ± 7.7° from a measurement of the inclination of the stellar spin axis with respect to the sky plane. Due to the young age and the weak tidal forcing of the system, we suggest that the orbit of WASP-84b is unlikely to have both realigned and circularized from the misaligned and/or eccentric orbit likely to have arisen from high-eccentricity migration. Therefore we conclude that the planet probably migrated via interaction with the protoplanetary disk. This would make it the first "hot Jupiter" () to have been shown to have migrated via this pathway. Further, we argue that the distribution of obliquities for planets orbiting cool stars (Teff < 6250 K) suggests that high-eccentricity migration is an important pathway for the formation of short-orbit, giant planets.

Original languageEnglish
Article numberL9
Number of pages6
JournalAstrophysical Journal Letters
Issue number1
Publication statusPublished - 10 Feb 2015


  • Planets and satellites: dynamical evolution and stability
  • Planet-disk interactions
  • Planets and satellites: individual (WASP-84b)
  • Planet-star interactions
  • Stars: individual (WASP-84)
  • Exoplanet HD 80606B
  • Tidal dissipation
  • Stellar obliquity
  • Giant planet
  • Long-period
  • Transit
  • Spin
  • System
  • Misalignment
  • Evolution


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