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arXiv · 2407.12898

JWST reveals a rapid and strong day side variability of 55 Cancri e

J. A. Patel·A. Brandeker·D. Kitzmann·D. J. M. Petit dit de la Roche·A. Bello-Arufe·K. Heng·E. Meier Valdés·C. M. Persson·M. Zhang·B. -O. Demory·V. Bourrier·A. Deline·D. Ehrenreich·M. Fridlund·R. Hu·M. Lendl·A. V. Oza·Y. Alibert·M. J. Hooton
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Abstract

The nature of the close-in rocky planet 55 Cnc e is puzzling despite having been observed extensively. Its optical and infrared occultation depths show temporal variability, in addition to a phase curve variability observed in the optical. We wish to explore the possibility that the variability originates from the planet being in a 3:2 spin-orbit resonance, thus showing different sides during occultations. We proposed and were awarded Cycle 1 time at the James Webb Space Telescope (JWST) to test this hypothesis. JWST/NIRCam observed five occultations (secondary eclipses), of which four were observed within a week, of the planet simultaneously at 2.1 and 4.5 μm. While the former gives band-integrated photometry, the latter provides a spectrum between 3.9-5.0 μm. We find that the occultation depths in both bandpasses are highly variable and change between a non-detection (-5 +/- 6 ppm and 7 +/- 9 ppm) to 96 +/- 8 ppm and 119 (+34) (-19) ppm at 2.1 μm and 4.5 μm, respectively. Interestingly, the variations in both bandpasses are not correlated and do not support the 3:2 spin-orbit resonance explanation. The measured brightness temperature at 4.5 μm varies between 873-2256 K and is lower than the expected dayside temperature of bare rock with no heat re-distribution (2500 K) which is indicative of an atmosphere. Our atmospheric retrieval analysis of occultation depth spectra at 4.5 μm finds that different visits statistically favour various atmospheric scenarios including a thin outgassed CO/CO2 atmosphere and a silicate rock vapour atmosphere. Some visits even support a flat line model. The observed variability could be explained by stochastic outgassing of CO/CO2, which is also hinted by retrievals. Alternatively, the variability, observed at both 2.1 and 4.5 μm, could be the result of a circumstellar patchy dust torus generated by volcanism on the planet.

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J. A. Patel, A. Brandeker, D. Kitzmann, D. J. M. Petit dit de la Roche, A. Bello-Arufe, K. Heng, E. Meier Valdés, C. M. Persson, M. Zhang, B. -O. Demory, V. Bourrier, A. Deline, D. Ehrenreich, M. Fridlund, R. Hu, M. Lendl, A. V. Oza, Y. Alibert, M. J. Hooton. 2024-07-17. JWST reveals a rapid and strong day side variability of 55 Cancri e. https://doi.org/10.1051/0004-6361%2F202450748

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