Variability in the Atmosphere of the Hot Jupiter Kepler-76b

Abstract: Phase curves and secondary eclipses of gaseous exoplanets are diagnostic of atmospheric composition and meteorology, and the long observational baseline and high photometric precision from the Kepler Mission make its dataset well-suited for exploring phase curve variability, which provides additional insights into atmospheric dynamics. Observations of the hot Jupiter Kepler-76b span more than 1,000 days, providing an ideal dataset to search for atmospheric variability. In this study, we find that Kepler-76b's secondary eclipse, with a depth of $87 \pm 6$ parts-per-million (ppm), corresponds to an effective temperature of 2,830$^{+50}_{-30}$ K. Our results also show clear indications of variability in Kepler-76b's atmospheric emission and reflectivity, with the phase curve amplitude typically $50.5 \pm 1.3$ ppm but varying between 35 and 70 ppm over tens of days. As is common for hot Jupiters, Kepler-76b's phase curve shows a discernible offset of $\left( 9 \pm 1.3 \right)^\circ$ eastward of the sub-stellar point and varying in concert with the amplitude. These variations may arise from the advance and retreat of thermal structures and cloud formations in Kepler-76b's atmosphere; the resulting thermal perturbations may couple with the super-rotation expected to transport aerosols, giving rise to a feedback loop. Looking forward, the TESS Mission can provide new insight into planetary atmospheres, with good prospects to observe both secondary eclipses and phase curves among targets from the mission. TESS's increased sensitivity in red wavelengths as compared to Kepler means that it will probably probe different aspects of planetary atmospheres.