A Precise Estimate of the Radius of the Exoplanet HD 149026b from   Spitzer Photometry
  We present Spitzer 8 micron transit observations of the extrasolar planet HD 149026b. At this wavelength, transit light curves are weakly affected by stellar limb-darkening, allowing for a simpler and more accurate determination of planetary parameters. We measure a planet-star radius ratio of Rp/Rs = 0.05158 +/- 0.00077, and in combination with ground-based data and independent constraints on the stellar mass and radius, we derive an orbital inclination of i = 85.4 +0.9/-0.8 degrees and a planet radius of Rp = 0.755 +/- 0.040 R_jup. These measurements further support models in which the planet is greatly enriched in heavy elements. 
Philip Nutzman, David Charbonneau, Joshua N. Winn, Heather A. Knutson,   Jonathan J. Fortney, Matthew J. Holman, Eric Agol