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 A159

Exoplanets from space -CHEOPS and PLATO ESA's next two projects (Phase 2)

Swedish National Space Board (65/19), 2020-01-01 -- 2022-12-31.

Swedish National Space Board (177/19), 2020-01-01 -- 2022-12-31.

Subject Categories

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

More information

Latest update

11/5/2024