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A transiting giant planet with a temperature between 250 K and 430 K


Of the over 400 known1 exoplanets, there are about 70 planets that transit their central star, a situation that permits the derivation of their basic parameters and facilitates investigations of their atmospheres. Some short-period planets2, including the first terrestrial exoplanet3,4 (CoRoT-7b), have been discovered using a space mission5 designed to find smaller and more distant planets than can be seen from the ground. Here we report transit observations of CoRoT-9b, which orbits with a period of 95.274 days on a low eccentricity of 0.11 ± 0.04 around a solar-like star. Its periastron distance of 0.36 astronomical units is by far the largest of all transiting planets, yielding a ‘temperate’ photospheric temperature estimated to be between 250 and 430 K. Unlike previously known transiting planets, the present size of CoRoT-9b should not have been affected by tidal heat dissipation processes. Indeed, the planet is found to be well described by standard evolution models6 with an inferred interior composition consistent with that of Jupiter and Saturn.

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Figure 1: Light curve and model fit of the CoRoT-9b transit.
Figure 2: CoRoT-9 radial velocities.
Figure 3: Evolutionary model for a CoRoT-9b like planet.
Figure 4: The orbital parameters of CoRoT-9b among extrasolar planets.

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The CoRoT space mission has been developed and is operated by CNES, with the contributions of Austria, Belgium, Brazil, ESA, Germany and Spain. CoRoT data are available to the public from the CoRoT archive: The team at IAC acknowledges support by grant ESP2007-65480-C02-02 of the Spanish Ministerio de Ciencia e Innovación. The German CoRoT Team (TLS and Univ. Cologne) acknowledges DLR grants 50OW0204, 50OW0603 and 50QP07011. Observations with the HARPS spectrograph were performed under the ESO programme ID 082.C-0120, and observations with the VLT/UVES under ID 081.C-0413(C).

Author Contributions H.J.D. coordinated the analysis and its interpretation. P. Barge., S.A., J.M.A., R.A., J.C., L.C., T.M., M.O., M.P. and B. Samuel contributed to the treatment of the light curve and the detection of the transits in the CoRoT data. F.B., D.Q., C.M., G.H., M.M., C.L., F. Pepe, A.H., W.B., S.A., S.U. and F. Pont prepared, performed and analysed radial velocity observations; A. Baglin, M.A., J.S., L.J., P. Bordé. A. Léger, A. Llebaria and P.B. contributed fundamentally to the definition, design and operation of the CoRoT instrument. A.E., B.T., S.C., R.D., M.F., M.G., M. Hidas, T.L., H.R., D.R., R.S., A.S., H.J.D., R.d.H., R.A., M.R., P.K., B. Stecklum and D.C. performed ground-based photometry; Sz.C., R.A., M.B. and A. S. Bonomo worked on light curve modelling and parameter fitting. M.D., H.B., D.G., J.-C.G., E.G. and M.F. constitute the team that performed the stellar typing and related observations. T.G., M. Havel, J.S., H.L., G.W. and S.F.-M. performed the modelling of the planet and the interpretation of its characteristics. All authors discussed the results and commented on the manuscript.

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Correspondence to H. J. Deeg.

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This file contains Supplementary Table 1: Measured radial velocities of CoRoT-9. (PDF 78 kb)

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Deeg, H., Moutou, C., Erikson, A. et al. A transiting giant planet with a temperature between 250 K and 430 K. Nature 464, 384–387 (2010).

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