Empirical constraints on the oblateness of an exoplanet

Joshua A. Carter, Joshua N. Winn

Research output: Contribution to journalArticle

43 Scopus citations

Abstract

We show that the gas giant exoplanet HD 189733b is less oblate than Saturn, based on Spitzer Space Telescope photometry of seven transits. The observable manifestations of oblateness would have been slight anomalies during the ingress and egress phases, as well as variations in the transit depth due to spin precession. Our nondetection of these effects gives the first empirical constraints on the shape of an exoplanet. The results are consistent with the theoretical expectation that the planetary rotation period and orbital period are synchronized, in which case the oblateness would be an order of magnitude smaller than our upper limits. Conversely, if HD 189733b is assumed to be in a synchronous, zero-obliquity state, then the data give an upper bound on the quadrupole moment of the planet (J2 < 0.068 with 95% confidence) that is too weak to constrain the interior structure of the planet. An Appendix describes a fast algorithm for computing the transit light curve of an oblate planet, which was necessary for our analysis.

Original languageEnglish (US)
Pages (from-to)1219-1229
Number of pages11
JournalAstrophysical Journal
Volume709
Issue number2
DOIs
StatePublished - Feb 1 2010
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • Methods: Numerical
  • Planetary systems
  • Techniques: Photometric

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