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We reassess the claimed detection of variability in the atmosphere of the hotJupiter HAT-P-7 b, reported by Armstrong et al. (2016). Although astronomersexpect hot Jupiters to have changing atmospheres, variability is challenging todetect. We looked for time variation in the phase curves of HAT-P-7 b in Keplerdata using similar methods to Armstrong et al. (2016), and identifiedapparently significant variations similar to what they found. Numerous testsshow the variations to be mostly robust to different analysis strategies.However, when we injected unchanging phase curve signals into the light curvesof other stars and searched for variability, we often saw similar levels ofvariations as in the HAT-P-7 light curve. Fourier analysis of the HAT-P-7 lightcurve revealed background red noise from stellar supergranulation on timescalessimilar to the planet's orbital period. Tests of simulated light curves withthe same level of noise as HAT-P-7's supergranulation show that this effectalone can cause the amplitude and phase offset variability we detect forHAT-P-7 b. Therefore, the apparent variations in HAT-P-7 b's atmosphere couldinstead be caused by non-planetary sources, most likely photometric variabilitydue to supergranulation on the host star.

Reassessing the Evidence for Time Variability in the Atmosphere of the Exoplanet HAT-P-7 b