The Transient Outgassed Atmosphere of 55 Cancri e

TL;DR

This paper investigates the transient, outgassed atmosphere of 55 Cancri e, proposing it explains observed eclipse variability through geochemical outgassing and atmospheric escape, with specific atmospheric compositions matching observations.

Contribution

It introduces the hypothesis of a transient, outgassed atmosphere on 55 Cancri e that accounts for its eclipse variability, supported by atmospheric modeling and observational predictions.

Findings

Pure CO2 or CO atmospheres explain optical eclipse depths.

Methane atmospheres are inconsistent with observations.

Atmospheric escape causes rapid temperature fluctuations.

Abstract

The enigmatic nature of 55 Cancri e has defied theoretical explanation. Any explanation needs to account for the observed variability of its secondary eclipse depth, which is at times consistent with zero in the visible/optical range of wavelengths -- a phenomenon that does not occur with its also variable infrared eclipses. Yet, despite this variability its transit depth remains somewhat constant in time and is inconsistent with opaque material filling its Hill sphere. The current study explores the possibility of a thin, transient, secondary atmosphere on 55 Cancri e that is sourced by geochemical outgassing. Its transient nature derives from the inability of outgassing to be balanced by atmospheric escape. As the outgassed atmosphere escapes and is replenished, it rapidly adjusts to radiative equilibrium and the temperature fluctuations cause the infrared eclipse depths to vary. Atmospheres of pure carbon dioxide or carbon monoxide produce sufficient Rayleigh scattering to explain the observed optical/visible eclipse depths, which vanish in the absence of an atmosphere and the presence of a dark rocky surface. Atmospheres of pure methane are ruled out because they produce insufficient Rayleigh scattering. Upcoming observations by the James Webb Space Telescope will potentially allow the atmospheric temperature and surface pressure, as well as the surface temperature, to be measured.