Short-period planets exhibit day–night temperature contrasts of hundreds to thousands of kelvin. They also exhibit eastward hotspot offsets whereby the hottest region on the planet is east of the substellar point1; this has been widely interpreted as advection of heat due to eastward winds2. We present thermal phase observations of the hot Jupiter CoRoT-2b obtained with the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. These measurements show the most robust detection to date of a westward hotspot offset of 23 ± 4°, in contrast with the nine other planets with equivalent measurements3,4,5,6,7,8,9,10. The peculiar infrared flux map of CoRoT-2b may result from westward winds due to non-synchronous rotation11 or magnetic effects12,13, or partial cloud coverage, that obscure the emergent flux from the planet’s eastern hemisphere14,15,16,17. Non-synchronous rotation and magnetic effects may also explain the planet’s anomalously large radius12,18. On the other hand, partial cloud coverage could explain the featureless dayside emission spectrum of the planet19,20. If CoRoT-2b is not tidally locked, then it means that our understanding of star–planet tidal interaction is incomplete. If the westward offset is due to magnetic effects, our result represents an opportunity to study an exoplanet’s magnetic field. If it has eastern clouds, then it means that a greater understanding of large-scale circulation on tidally locked planets is required.
Your institute does not have access to this article
Open Access articles citing this article.
Space Science Reviews Open Access 01 December 2020
Subscribe to Nature+
Get immediate online access to the entire Nature family of 50+ journals
Subscribe to Journal
Get full journal access for 1 year
only $8.25 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Get time limited or full article access on ReadCube.
All prices are NET prices.
Knutson, H. A. et al. A map of the day-night contrast of the extrasolar planet HD 189733b. Nature 447, 183–186 (2007).
Showman, A. P. & Guillot, T. Atmospheric circulation and tides of “51 Pegasus b-like” planets. Astron. Astrophys. 385, 166–180 (2002).
Cowan, N. B. et al. Thermal phase variations of WASP-12b: defying predictions. Astrophys. J. 747, 82 (2012).
Knutson, H. A. et al. 3.6 and 4.5 μm phase curves and evidence for non-equilibrium chemistry in the atmosphere of extrasolar planet HD 189733b. Astrophys. J. 754, 22 (2012).
Maxted, P. F. L. et al. Spitzer 3.6 and 4.5 μm full-orbit light curves of WASP-18. Mon. Not. R. Astron. Soc. 428, 2645–2660 (2013).
Zellem, R. T. et al. The 4.5 μm full-orbit phase curve of the hot Jupiter HD 209458b. Astrophys. J. 790, 53 (2014).
Wong, I. et al. 3.6 and 4.5 μm phase curves of the highly irradiated eccentric hot Jupiter WASP-14b. Astrophys. J. 811, 122 (2015).
Wong, I. et al. 3.6 and 4.5 μm Spitzer phase curves of the highly irradiated hot Jupiters WASP-19b and HAT-P-7b. Astrophys. J. 823, 122 (2016).
Demory, B.-O., Gillon, M., Madhusudhan, N. & Queloz, D. Variability in the super-Earth 55 Cnc e. Mon. Not. R. Astron. Soc. 455, 2018–2027 (2016).
Stevenson, K. B. et al. Spitzer phase curve constraints for WASP-43b at 3.6 and 4.5 μm. Astron. J. 153, 68 (2017).
Rauscher, E. & Kempton, E. M. R. The atmospheric circulation and observable properties of non-synchronously rotating hot Jupiters. Astrophys. J. 790, 79 (2014).
Rogers, T. M. & Komacek, T. D. Magnetic effects in hot Jupiter atmospheres. Astrophys. J. 794, 132 (2014).
Rogers, T. M. Constraints on the magnetic field strength of HAT-P-7 b and other hot giant exoplanets. Nat. Astron. 1, 0131 (2017).
Demory, B.-O. et al. Inference of inhomogeneous clouds in an exoplanet atmosphere. Astrophys. J. Lett. 776, L25 (2013).
Parmentier, V., Fortney, J. J., Showman, A. P., Morley, C. & Marley, M. S. Transitions in the cloud composition of hot Jupiters. Astrophys. J. 828, 22 (2016).
Lee, G., Dobbs-Dixon, I., Helling, C., Bognar, K. & Woitke, P. Dynamic mineral clouds on HD 189733b. I. 3D RHD with kinetic, non-equilibrium cloud formation. Astron. Astrophys. 594, A48 (2016).
Roman, M. & Rauscher, E. Modeling the effects of inhomogeneous aerosols on the hot Jupiter Kepler-7b’s atmospheric circulation. Astrophys. J. 850, 17 (2017).
Guillot, T. & Havel, M. An analysis of the CoRoT-2 system: a young spotted star and its inflated giant planet. Astron. Astrophys. 527, A20 (2011).
Moses, J. I., Madhusudhan, N., Visscher, C. & Freedman, R. S. Chemical consequences of the C/O ratio on hot Jupiters: examples from WASP-12b, CoRoT-2b, XO-1b, and HD 189733b. Astrophys. J. 763, 25 (2013).
Wilkins, A. N. et al. The emergent 1.1–1.7 μm spectrum of the exoplanet CoRoT-2b as measured using the hubble space telescope. Astrophys. J. 783, 113 (2014).
Alonso, R. et al. The secondary eclipse of the transiting exoplanet CoRoT-2b. Astron. Astrophys. 501, L23–L26 (2009).
Snellen, I. A. G., de Mooij, E. J. W. & Burrows, A. Bright optical day-side emission from extrasolar planet CoRoT-2b. Astron. Astrophys. 513, A76 (2010).
Alonso, R., Deeg, H. J., Kabath, P. & Rabus, M. Ground-based near-infrared observations of the secondary eclipse of CoRoT-2b. Astron. J. 139, 1481–1485 (2010).
Gillon, M. et al. The thermal emission of the young and massive planet CoRoT-2b at 4.5 and 8 μm. Astron. Astrophys. 511, A3 (2010).
Deming, D. et al. Warm Spitzer photometry of the transiting exoplanets CoRoT-1 and CoRoT-2 at secondary eclipse. Astrophys. J. 726, 95 (2011).
Schwartz, J. C. & Cowan, N. B. Balancing the energy budget of short-period giant planets: evidence for reflective clouds and optical absorbers. Mon. Not. R. Astron. Soc. 449, 4192–4203 (2015).
Delorme, P. et al. In-depth study of moderately young but extremely red, very dusty substellar companion HD206893B. Astron. Astrophys. https://doi.org/10.1051/0004-6361/201731145 (2017).
Rauscher, E. & Kempton, E. M. R. Erratum: “The atmospheric circulation and observable properties of non-synchronously rotating hot Jupiters”. Astrophys. J. 799, 241 (2015).
Armstrong, D. J. et al. Variability in the atmosphere of the hot giant planet HAT-P-7 b. Nat. Astron. 1, 0004 (2016).
Yadav, R. K. & Thorngren, D. P. Estimating the magnetic field strength in hot Jupiters. Astrophys. J. Lett. 849, L12 (2017).
Menou, K. Magnetic scaling laws for the atmospheres of hot giant exoplanets. Astrophys. J. 745, 138 (2012).
Kempton, E. M.-R., Bean, J. L. & Parmentier, V. An observational diagnostic for distinguishing between clouds and haze in hot exoplanet atmospheres. Astrophys. J. Lett. 845, L20 (2017).
Feng, Y. K. et al. The impact of non-uniform thermal structure on the interpretation of exoplanet emission spectra. Astrophys. J. 829, 52 (2016).
Arras, P. & Socrates, A. Thermal tides in fluid extrasolar planets. Astrophys. J. 714, 1–12 (2010).
Alonso, R. et al. Transiting exoplanets from the CoRoT space mission. II. CoRoT-Exo-2b: a transiting planet around an active G star. Astron. Astrophys. 482, L21–L24 (2008).
Fazio, G. G. et al. The infrared array camera (IRAC) for the Spitzer Space Telescope. Astrophys. J. Suppl. Ser. 154, 10–17 (2004).
Werner, M. W. et al. The Spitzer Space Telescope mission. Astrophys. J. Suppl. Ser. 154, 1–9 (2004).
Cabrera, J. et al. Planetary transit candidates in CoRoT-LRc01 field. Astron. Astrophys. 506, 501–517 (2009).
Skrutskie, M. F., Cutri, R. M. et al. The Two Micron All Sky Survey (2MASS). Astron. J. 131, 1163–1183 (2006)
Kreidberg, L. batman: BAsic Transit Model cAlculatioN in python. Publ. Astron. Soc. Pacific 127, 1161–1165 (2015).
Mandel, K. & Agol, E. Analytic light curves for planetary transit searches. Astrophys. J. Lett. 580, L171–L175 (2002).
Schröter, S. et al. The corona and companion of CoRoT-2a. Insights from X-rays and optical spectroscopy. Astron. Astrophys. 532, A3 (2011).
Lanza, A. F. et al. Magnetic activity in the photosphere of CoRoT-Exo-2a. Active longitudes and short-term spot cycle in a young Sun-like star. Astron. Astrophys. 493, 193–200 (2009).
Cowan, N. B. & Agol, E. Inverting phase functions to map exoplanets. Astrophys. J. Lett. 678, L129 (2008).
Charbonneau, D. et al. Detection of thermal emission from an extrasolar planet. Astrophys. J. 626, 523–529 (2005).
Stevenson, K. B. et al. Transit and eclipse analyses of the exoplanet HD 149026b using BLISS mapping. Astrophys. J. 754, 136 (2012).
Ingalls, J. G. et al. Repeatability and accuracy of exoplanet eclipse depths measured with post-cryogenic spitzer. Astron. J. 152, 44 (2016).
Schwartz, J. C. & Cowan, N. B. Knot a bad idea: testing BLISS mapping for Spitzer space telescope photometry. Publ. Astron. Soc. Pacific 129, 014001 (2017).
Deming, D. et al. Spitzer Secondary Eclipses of the Dense, Modestly-irradiated, Giant Exoplanet HAT-P-20b Using Pixel-level Decorrelation. Astrophys. J. 805, 132 (2015).
Benneke, B. et al. Spitzer observations confirm and rescue the habitable-zone super-earth K2-18b for future characterization. Astrophys. J. 834, 187 (2017).
Foreman-Mackey, D., Hogg, D. W., Lang, D. & Goodman, J. emcee: the MCMC hammer. Publ. Astron. Soc. Pacific 125, 306 (2013).
Espinoza, N. & Jordán, A. Limb darkening and exoplanets: testing stellar model atmospheres and identifying biases in transit parameters. Mon. Not. R. Astron. Soc. 450, 1879–1899 (2015).
Kipping, D. M. Efficient, uninformative sampling of limb darkening coefficients for two-parameter laws. Mon. Not. R. Astron. Soc. 435, 2152–2160 (2013).
Keating, D. & Cowan, N. B. Revisiting the energy budget of WASP-43b: enhanced day-night heat transport. Astrophys. J. Lett. 849, L5 (2017).
Schwarz, G. et al. Estimating the dimension of a model. Ann. Statistics 6, 461–464 (1978).
Wit, E., Heuvel, E. & Romeijn, J. ‘All models are wrong…’: an introduction to model uncertainty. Stat. Neerl. 66, 217–236 (2012).
Kass, R. E. & Raftery, A. E. Bayes factors. J. Am. Statistical Assoc. 90, 773–795 (1995).
Zhang, M. et al. Phase curves of WASP-33b and HD 149026b and a new correlation between phase curve offset and irradiation temperature. Preprint at http://arxiv.org/abs/1710.07642 (2017).
Cowan, N. B., Voigt, A. & Abbot, D. S. Thermal phases of Earth-like planets: estimating thermal inertia from eccentricity, obliquity, and diurnal forcing. Astrophys. J. 757, 80 (2012).
Cowan, N. B. & Agol, E. The statistics of albedo and heat recirculation on hot exoplanets. Astrophys. J. 729, 54 (2011).
Perez-Becker, D. & Showman, A. P. Atmospheric heat redistribution on hot Jupiters. Astrophys. J. 776, 134 (2013).
Schwartz, J. C., Kashner, Z., Jovmir, D. & Cowan, N. B. Phase offsets and the energy budgets of hot Jupiters. Astrophys. J. 850, 154 (2017).
STScI Development Team pysynphot Synthetic photometry software package (2013); http://ascl.net/1303.023
Hansen, C. J., Schwartz, J. C. & Cowan, N. B. Features in the broad-band eclipse spectra of exoplanets: signal or noise? Mon. Not. R. Astron. Soc. 444, 3632–3640 (2014).
Perna, R., Menou, K. & Rauscher, E. Magnetic drag on hot jupiter atmospheric winds. Astrophys. J. 719, 1421–1426 (2010).
Van der Walt, S., Colbert, C. C. & Varoquaux, G. The NumPy array: a structure for efficient numerical computation. Comp. Sci. Eng. 13, 22–30 (2011).
Astropy Collaboration. Astropy: a community python package for astronomy. Astron. Astrophys. 558, A33 (2013).
Hunter, J. D. Matplotlib: a 2D graphics environment. Comp. Sci. Eng. 9, 90–95 (2007).
Foreman-Mackey, D. corner.py: scatterplot matrices in python. J. Open Source Software 1, 24 (2016).
Pérez, F. & Granger, B. E. IPython: a system for interactive scientific computing. Comp. Sci. Eng. 9, 21–29 (2007).
L.D. thanks S. Carey, J. Ingalls and W. Glaccum from the Spitzer IRAC team for the helpful discussions that contributed to the reduction of the data. Funding for this work was provided in part by the Natural Sciences and Engineering Research Council of Canada (NSERC) discovery grant and the California Institute of Technology’s Infrared Processing and Analysis Center (Caltech/IPAC) Visiting Graduate Research Fellowship. Work by S.S. was funded by the Google Summer of Code programme. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech.
The authors declare no competing financial interests.
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary Tables 1–6, Supplementary Figures 1–15, Supplementary text, Supplementary references.
Binned data supporting Supplementary Figure 1.
Full data supporting Supplementary Figure 1.
Data supporting top panel of Supplementary Figure 13.
Data supporting bottom panel of Supplementary Figure 13.
Data supporting Supplementary Figure 4.
Data supporting Supplementary Figure 14.
About this article
Cite this article
Dang, L., Cowan, N.B., Schwartz, J.C. et al. Detection of a westward hotspot offset in the atmosphere of hot gas giant CoRoT-2b. Nat Astron 2, 220–227 (2018). https://doi.org/10.1038/s41550-017-0351-6
Experimental Astronomy (2022)
Nature Astronomy (2020)
Nature Astronomy (2020)
Space Science Reviews (2020)
Nature Astronomy (2019)