Variability in the super-Earth 55 Cnc e

TL;DR

This study reports a significant detection of variability in the thermal emission of super-Earth 55 Cnc e, suggesting dynamic atmospheric or surface processes, which challenges previous assumptions of featureless spectra in such planets.

Contribution

First detection of thermal emission variability in a super-Earth, indicating complex surface or atmospheric activity not explained by star spots or simple atmospheric changes.

Findings

Thermal emission from 55 Cnc e varies by a factor of 3.7.

Variability cannot be explained by star spots or short-term atmospheric changes.

Large-scale surface activity or circumstellar material are plausible causes.

Abstract

Considerable progress has been made in recent years in observations of atmospheric signatures of giant exoplanets, but processes in rocky exoplanets remain largely unknown due to major challenges in observing small planets. Numerous efforts to observe spectra of super-Earths, exoplanets with masses of 1-10 Earth masses, have thus far revealed only featureless spectra. In this paper we report a 4-$\sigma$ detection of variability in the dayside thermal emission from the transiting super-Earth 55 Cancri e. Dedicated space-based monitoring of the planet in the mid-infrared over eight eclipses revealed the thermal emission from its dayside atmosphere varying by a factor 3.7 between 2012 and 2013. The amplitude and trend of the variability are not explained by potential influence of star spots or by local thermal or compositional changes in the atmosphere over the short span of the observations. The possibility of large scale surface activity due to strong tidal interactions possibly similar to Io, or the presence of circumstellar/circumplanetary material appear plausible and motivate future long-term monitoring of the planet.