The Albedos of Kepler's Close-in super-Earths

TL;DR

This study analyzes the reflective properties of 97 close-in super-Earths from Kepler data, revealing their geometric albedos are generally higher than hot Jupiters and vary significantly, indicating diverse surface and atmospheric characteristics.

Contribution

It introduces a novel hierarchical Bayesian approach to characterize the population-level albedos of close-in super-Earths using occultation data.

Findings

Median geometric albedos range from 0.16 to 0.30 after decontamination.

Super-Earth albedos are statistically larger than hot Jupiters.

Some planets, like Kepler-10b, have albedos exceeding 0.4.

Abstract

Exoplanet research focusing on the characterization of super-Earths is currently limited to those handful targets orbiting bright stars that are amenable to detailed study. This Letter proposes to look at alternative avenues to probe the surface and atmospheric properties of this category of planets, known to be ubiquitous in our galaxy. I conduct Markov Chain Monte Carlo lightcurve analyses for 97 Kepler close-in $R_P \lesssim 2.0 R_{\oplus}$ super-Earth candidates with the aim to detect their occultations at visible wavelengths. Brightness temperatures and geometric albedos in the Kepler bandpass are constrained for 27 super-Earth candidates. A hierarchical Bayesian modeling approach is then employed to characterize the population-level reflective properties of these close-in super-Earths. I find median geometric albedos $A_g$ in the Kepler bandpass ranging between 0.16 and 0.30, once decontaminated from thermal emission. These super-Earths geometric albedos are statistically larger than for hot Jupiters, which have medians $A_g$ ranging between 0.06 and 0.11. A subset of objects, including Kepler-10b, exhibit significantly larger albedos ($A_g\gtrsim$0.4). I argue that a better understanding of the incidence of stellar irradiation on planetary surface and atmospheric processes is key to explain the diversity in albedos observed for close-in super-Earths.