55 Cancri e’s occultation captured with CHEOPS

Abstract

Past occultation and phase-curve observations of the ultra-short period super-Earth 55 Cnc e obtained at visible and infrared wavelengths have been challenging to reconcile with a planetary reflection and emission model. In this study, we analyse a set of 41 occultations obtained over a two-year timespan with the CHEOPS satellite. We report the detection of 55 Cnc e's occultation with an average depth of 12 ± 3 ppm. We derive a corresponding 2-σ upper limit on the geometric albedo of A g < 0.55 once decontaminated from the thermal emission measured by Spitzer at 4.5µm. CHEOPS's photometric performance enables, for the first time, the detection of individual occultations of this super-Earth in the visible and identifies short-timescale photometric corrugations likely induced by stellar granulation. We also find a clear 47.3-day sinusoidal pattern in the time-dependent occultation depths that we are unable to relate to stellar noise, nor instrumental systematics, but whose planetary origin could be tested with upcoming JWST occultation observations of this iconic super-Earth.

The Transient Outgassed Atmosphere of 55 Cancri e

“…I now suggest an alternative interpretation of the observations reported by Demory et al (2016aDemory et al ( , 2016b, Tamburo et al (2018), Demory et al (2023), and Meier Valdés et al (2023). When the optical/visible secondary eclipse depths are consistent with being zero, this is interpreted as the observations probing mainly the bare rocky surface of the dayside of 55 Cancri e. To be consistent with zero optical/visible eclipse depth, the geometric albedo of the surface must be close to zero.…”

“…These recently reported observations by the CHEOPS space telescope (Meier Valdés et al 2022Demory et al 2023), as well as upcoming eclipse observations by the James Webb Space Telescope (JWST), 4 motivate a qualitatively different approach of interpreting the data of 55 Cancri e. In the current study, it is suggested that the reported observations collectively describe a thin, transient, outgassed atmosphere that does not survive over long timescales, because atmospheric escape dominates the outgassing flux.…”

“…There is a rich debate on how the treatment of the spectral energy distribution of the 55 Cancri e star affects the interpretation of the secondary eclipses of 55 Cancri e (Crossfield 2012). To check the sensitivity of the computed eclipse depths to this issue, the PHOENIX model spectrum of 55 Cancri e used by Demory et al (2023) and Meier Valdés et al (2023) is used. The preceding expressions for D th and D r are generalized by substituting B λ (T å ) with F å /π, where F å is the PHOENIX model spectrum (in flux, rather than intensity, units).…”

“…A key hint to understanding the nature of 55 Cancri e lies in the variability of its secondary eclipses, both in the optical/ visible (Meier Valdés et al 2022;Demory et al 2023;Meier Valdés et al 2023) and infrared (Demory et al 2016a;Tamburo et al 2018) range of wavelengths. At times, the optical/visible secondary eclipses become consistent with zero (Demory et al 2023;Meier Valdés et al 2023), but this phenomenon does not occur with the infrared secondary eclipses (Demory et al 2016a;Tamburo et al 2018). Yet its primary transit depths remain somewhat constant (Tamburo et al 2018;Meier Valdés et al 2023).…”

A Nondetection of Iron in the First High-resolution Emission Study of the Lava Planet 55 Cnc e

“…Repeating this exercise in the CHEOPS band yields occultation depths of 5 ppm and 10 ppm for our BSE and Venusian models, respectively. While these models at first glance are discrepant from existing single Spitzer (Mercier et al 2022) and CHEOPS (Demory et al 2023) observed occultation depths of 209 47 50 -+ ppm and 12 ± 3 ppm, respectively, the models fall within the full range of observed variable occultations (Demory et al , 2023. In light of the lack of consensus on the observed variability's origin, it is not immediately clear whether our models are constrained by existing photometric data.…”