Detection of Thermal Emission from a Super-Earth

TL;DR

This study reports the first detection of infrared thermal emission from the super-Earth 55 Cnc e using Warm Spitzer, revealing insights into its temperature, albedo, and heat transport properties.

Contribution

It presents the first measurement of thermal emission from 55 Cnc e, combining multiple datasets with a global MCMC analysis to determine its brightness temperature and orbital characteristics.

Findings

Detected a 131±28 ppm occultation depth at 4.5 microns.

Derived a brightness temperature of 2360±300 K.

Constrained the orbital eccentricity to less than 0.06.

Abstract

We report on the detection of infrared light from the super-Earth 55 Cnc e, based on four occultations obtained with Warm Spitzer at 4.5 microns. Our data analysis consists of a two-part process. In a first step, we perform individual analyses of each dataset and compare several baseline models to optimally account for the systematics affecting each lightcurve. We apply independent photometric correction techniques, including polynomial detrending and pixel-mapping, that yield consistent results at the 1-sigma level. In a second step, we perform a global MCMC analysis including all four datasets, that yields an occultation depth of 131+-28ppm, translating to a brightness temperature of 2360+-300 K in the IRAC-4.5 micron channel. This occultation depth suggests a low Bond albedo coupled to an inefficient heat transport from the planetary dayside to the nightside, or else possibly that the 4.5-micron observations probe atmospheric layers that are hotter than the maximum equilibrium temperature (i.e., a thermal inversion layer or a deep hot layer). The measured occultation phase and duration are consistent with a circular orbit and improves the 3-sigma upper limit on 55 Cnc e's orbital eccentricity from 0.25 to 0.06.