WASP-4b Arrived Early for the TESS Mission

L. G. Bouma, J. N. Winn, C. Baxter, W. Bhatti, F. Dai, T. Daylan, J. M. Désert, M. L. Hill, S. R. Kane, K. G. Stassun, J. Villasenor, G. R. Ricker, R. Vanderspek, D. W. Latham, S. Seager, J. M. Jenkins, Z. Berta-Thompson, K. Colón, M. Fausnaugh, Ana GliddenN. Guerrero, J. E. Rodriguez, J. D. Twicken, B. Wohler

Research output: Contribution to journalArticlepeer-review

60 Scopus citations


The Transiting Exoplanet Survey Satellite (TESS) recently observed 18 transits of the hot Jupiter WASP-4b. The sequence of transits occurred 81.6 ± 11.7 s earlier than had been predicted, based on data stretching back to 2007. This is unlikely to be the result of a clock error, because TESS observations of other hot Jupiters (WASP-6b, 18b, and 46b) are compatible with a constant period, ruling out an 81.6 s offset at the 6.4σ level. The 1.3 day orbital period of WASP-4b appears to be decreasing at a rate of ms per year. The apparent period change might be caused by tidal orbital decay or apsidal precession, although both interpretations have shortcomings. The gravitational influence of a third body is another possibility, though at present there is minimal evidence for such a body. Further observations are needed to confirm and understand the timing variation.

Original languageEnglish (US)
Article number217
JournalAstronomical Journal
Issue number6
StatePublished - 2019

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • binaries: close
  • planet star interactions
  • planets and satellites: individual (WASP-4b, WASP-5b, WASP-6b, WASP-12b, WASP-18b, WASP-46b)


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