The stable climate of KELT-9b

K. Jones*, B. M. Morris, B.-O. Demory, K. Heng, M. J. Hooton, N. Billot, D. Ehrenreich, S. Hoyer, A. E. Simon, M. Lendl, O. D. S. Demangeon, S. G. Sousa, A. Bonfanti, T. G. Wilson, S. Salmon, Sz. Csizmadia, H. Parviainen, G. Bruno, Y. Alibert, R. AlonsoG. Anglada, T. Bárczy, D. Barrado, S. C. C. Barros, W. Baumjohann, M. Beck, T. Beck, W. Benz, X. Bonfils, A. Brandeker, C. Broeg, J. Cabrera, S. Charnoz, A. Collier Cameron, M. B. Davies, M. Deleuil, A. Deline, L. Delrez, A. Erikson, A. Fortier, L. Fossati, M. Fridlund, D. Gandolfi, M. Gillon, M. Güdel, K. G. Isaak, L. L. Kiss, J. Laskar, A. Lecavelier des Etangs, C. Lovis, D. Magrin, P. F. L. Maxted, V. Nascimbeni, G. Olofsson, R. Ottensamer, I. Pagano, E. Pallé, G. Peter, G. Piotto, D. Pollacco, D. Queloz, R. Ragazzoni, N. Rando, F. Ratti, H. Rauer, C. Reimers, I. Ribas, N. C. Santos, G. Scandariato, D. Ségransan, A. M. S. Smith, M. Steller, Gy. M. Szabó, N. Thomas, S. Udry, V. Van Grootel, I. Walter, N. A. Walton, W. Wang Jungo

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Even among the most irradiated gas giants, so-called ultra-hot Jupiters, KELT-9b stands out as the hottest planet thus far discovered with a dayside temperature of over 4500 K. At these extreme irradiation levels, we expect an increase in heat redistribution efficiency and a low Bond albedo owed to an extended atmosphere with molecular hydrogen dissociation occurring on the planetary dayside. We present new photometric observations of the KELT-9 system throughout 4 full orbits and 9 separate occultations obtained by the 30 cm space telescope CHEOPS. The CHEOPS bandpass, located at optical wavelengths, captures the peak of the thermal emission spectrum of KELT-9b. In this work we simultaneously analyse CHEOPS phase curves along with public phase curves from TESS and Spitzer to infer joint constraints on the phase curve variation, gravity-darkened transits, and occultation depth in three bandpasses, as well as derive 2D temperature maps of the atmosphere at three different depths. We find a day-night heat redistribution efficiency of ~0.3 which confirms expectations of enhanced energy transfer to the planetary nightside due to dissociation and recombination of molecular hydrogen. We also calculate a Bond albedo consistent with zero. We find no evidence of variability of the brightness temperature of the planet, excluding variability greater than 1%.
Original languageEnglish
Article numberA118
Number of pages19
JournalAstronomy & Astrophysics
Early online date19 Oct 2022
Publication statusPublished - 19 Oct 2022


  • Techniques: photometric
  • Instrumentation: photometers
  • Planets and satellites: atmospheres
  • Planets and satellites: gaseous planets
  • Eclipses
  • Occultations


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