JWST reveals the rapid and strong day-side variability of 55 Cancri e
Journal article, 2024
Context. The nature of the close-in rocky planet 55 Cnce is puzzling, despite it having been observed extensively. Its optical and infrared occultation depths show temporal variability, in addition to a phase curve variability observed in the optical. Aims. We wish to explore the possibility that the variability originates from the planet being in a 3:2 spin- orbit resonance, and 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. Methods. JWST/NIRCam (Near Infrared Camera) observed five occultations (secondary eclipses) of the planet - of which four were observed within a week - 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. Results. 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 119-19+34 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 day-side temperature of bare rock with no heat redistribution (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. Conclusions. The observed variability could be explained by stochastic outgassing of CO/CO2, which is also hinted at 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.
Planets and satellites: atmospheres
Planets and satellites: terrestrial planets
Techniques: photometric
Planets and satellites: individual: 55 Cnc e
Techniques: spectroscopic
Author
J. A. Patel
Stockholm University
A. Brandeker
Stockholm University
D. Kitzmann
University of Bern
Dominique J.M. Petit dit de la Roche
University of Geneva
Aaron Bello-Arufe
California Institute of Technology (Caltech)
Kevin Heng
The University of Warwick
University College London (UCL)
University of Bern
Ludwig Maximilian University of Munich (LMU)
E. Meier Valdes
University of Bern
Carina Persson
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Michael Zhang
University of Chicago
B.O. Demory
University of Bern
V. Bourrier
University of Geneva
A. Deline
University of Geneva
D. Ehrenreich
University of Geneva
Malcolm Fridlund
Leiden University
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Renyu Hu
California Institute of Technology (Caltech)
M. Lendl
University of Geneva
A. V. Oza
California Institute of Technology (Caltech)
Y. Alibert
University of Bern
M.J. Hooton
University of Cambridge
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 690 A159Exoplanets from space -CHEOPS and PLATO ESA's next two projects (Phase 2)
Swedish National Space Board (177/19), 2020-01-01 -- 2022-12-31.
Swedish National Space Board (65/19), 2020-01-01 -- 2022-12-31.
Subject Categories (SSIF 2011)
Aerospace Engineering
Astronomy, Astrophysics and Cosmology
Probability Theory and Statistics
DOI
10.1051/0004-6361/202450748
Related datasets
URI: https://cdsarc.cds.unistra.fr/cgi-bin/qcat?J/ A+A/690/A159