Nature 447, 183-186 (10 May 2007) | doi:10.1038/nature05782; Received 8 February 2007; Accepted 23 March 2007

A map of the day–night contrast of the extrasolar planet HD 189733b

Heather A. Knutson1, David Charbonneau1, Lori E. Allen1, Jonathan J. Fortney2,3, Eric Agol4, Nicolas B. Cowan4, Adam P. Showman5, Curtis S. Cooper5 & S. Thomas Megeath6

  1. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA
  2. Space Science and Astrobiology Division, NASA Ames Research Center, MS 245-3, Moffett Field, California 94035, USA
  3. SETI Institute, 515 N. Whisman Road, Mountain View, California 94043, USA
  4. Department of Astronomy, Box 351580, University of Washington, Seattle, Washington 98195, USA
  5. Lunar and Planetary Laboratory and Department of Planetary Sciences, University of Arizona, Tucson, Arizona 85721, USA
  6. Department of Physics and Astronomy, University of Toledo, 2801 West Bancroft Street, Toledo, Ohio 43606, USA

Correspondence to: Heather A. Knutson1 Correspondence and requests for materials should be addressed to H.A.K. (Email: hknutson@cfa.harvard.edu).

'Hot Jupiter' extrasolar planets are expected to be tidally locked because they are close (<0.05 astronomical units, where 1 au is the average Sun–Earth distance) to their parent stars, resulting in permanent daysides and nightsides. By observing systems where the planet and star periodically eclipse each other, several groups have been able to estimate the temperatures of the daysides of these planets1, 2, 3. A key question is whether the atmosphere is able to transport the energy incident upon the dayside to the nightside, which will determine the temperature at different points on the planet's surface. Here we report observations of HD 189733, the closest of these eclipsing planetary systems4, 5, 6, over half an orbital period, from which we can construct a 'map' of the distribution of temperatures. We detected the increase in brightness as the dayside of the planet rotated into view. We estimate a minimum brightness temperature of 973 plusminus 33 K and a maximum brightness temperature of 1,212 plusminus 11 K at a wavelength of 8 mum, indicating that energy from the irradiated dayside is efficiently redistributed throughout the atmosphere, in contrast to a recent claim for another hot Jupiter7. Our data indicate that the peak hemisphere-integrated brightness occurs 16 plusminus 6° before opposition, corresponding to a hotspot shifted east of the substellar point. The secondary eclipse (when the planet moves behind the star) occurs 120 plusminus 24 s later than predicted, which may indicate a slightly eccentric orbit.


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