55 Cancri e's occultation captured with CHEOPS

TL;DR

This study reports the first detection of 55 Cnc e's occultation in visible light using CHEOPS, providing new insights into its albedo and potential planetary signals amidst stellar noise.

Contribution

It presents the first individual occultation detections of 55 Cnc e in visible light and identifies a planetary-origin sinusoidal pattern in occultation depths.

Findings

Detected 55 Cnc e occultation with 12±3 ppm depth

Set an upper limit on geometric albedo A_g < 0.55

Found a 47.3-day sinusoidal pattern in occultation depths

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 $12\pm3$ ppm. We derive a corresponding 2-$\sigma$ upper limit on the geometric albedo of $A_g < 0.55$ once decontaminated from the thermal emission measured by Spitzer at 4.5$\mu$m. 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.