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# Infrared radiation from an extrasolar planet

## Abstract

A class of extrasolar giant planets—the so-called ‘hot Jupiters’ (ref. 1)—orbit within 0.05 au of their primary stars (1 au is the Sun–Earth distance). These planets should be hot and so emit detectable infrared radiation2. The planet HD 209458b (refs 3, 4) is an ideal candidate for the detection and characterization of this infrared light because it is eclipsed by the star. This planet has an anomalously large radius (1.35 times that of Jupiter5), which may be the result of ongoing tidal dissipation6, but this explanation requires a non-zero orbital eccentricity ( 0.03; refs 6, 7), maintained by interaction with a hypothetical second planet. Here we report detection of infrared (24 µm) radiation from HD 209458b, by observing the decrement in flux during secondary eclipse, when the planet passes behind the star. The planet's 24-µm flux is 55 ± 10 µJy (1σ), with a brightness temperature of 1,130 ± 150 K, confirming the predicted heating by stellar irradiation2,8. The secondary eclipse occurs at the midpoint between transits of the planet in front of the star (to within ± 7 min, 1σ), which means that a dynamically significant orbital eccentricity is unlikely.

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We thank all the personnel of the Spitzer telescope and the MIPS instrument, who ultimately made these measurements possible. L.J.R. is a National Research Council Associate at NASA's Goddard Space Flight Center. ## Author information ### Authors and Affiliations Authors ### Corresponding author Correspondence to Drake Deming. ## Ethics declarations ### Competing interests The authors declare that they have no competing financial interests. ## Supplementary information ### Supplementary Figure S1 Sample flat-fielded and flux-calibrated MIPS image of HD 209458 produced by the Spitzer S11.0 data processing pipeline. (PDF 95 kb) ### Supplementary Figure S2 A tabulation of the temporal deviations in normalized intensity for all detector pixels not containing the star, with Fourier power spectra, for a sample data block. Shows gaussian white noise properties. (PDF 70 kb) ### Supplementary Figure S3 A tabulation of the temporal deviations in normalized intensity for all detector pixels within ± 10 pixels of the the star, for a sample data block. Shows gaussian property of the noise. (PDF 47 kb) ### Supplementary Figure Legends Legends to accompany Supplementary Figures S1-S3. (DOC 23 kb) ## Rights and permissions Reprints and Permissions ## About this article ### Cite this article Deming, D., Seager, S., Richardson, L. et al. Infrared radiation from an extrasolar planet. Nature 434, 740–743 (2005). https://doi.org/10.1038/nature03507 Download citation • Received: • Accepted: • Published: • Issue Date: • DOI: https://doi.org/10.1038/nature03507 ## This article is cited by • ### Oxygen as atmospheric thermometer • Matteo Brogi Nature Astronomy (2022) • ### The$11-billion Webb telescope aims to probe the early Universe

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