Average Albedos of Close-in Super-Earths and Super-Neptunes from Statistical Analysis of Long-cadence Kepler Secondary Eclipse Data

Abstract

We present the results of our work to determine the average albedo for small, close-in planets in the Kepler candidate catalog. We have adapted our method of averaging short cadence light curves of multiple Kepler planet candidates to long cadence data, in order to detect an average albedo for the group of candidates. Long cadence data exist for many more candidates than the short cadence, and so we separate the candidates into smaller radius bins than in our previous work: 1-2 R ⊕ , 2-4 R ⊕ , and 4-6 R ⊕ . We find that on average, all three groups appear darker than suggested by the short cadence result, but not as dark as many hot Jupiters. The average geometric albedos for the three groups are 0.11 ± 0.06, 0.05 ± 0.04, and 0.11 ± 0.08, respectively, for the case where heat is uniformly distributed about the planet. If heat redistribution is inefficient, the albedos are even lower, since there will be a greater thermal contribution to the total light from the planet. We confirm that newly-identified false positive Kepler Object of Interest (KOI) 1662.01 is indeed an eclipsing binary at twice the period listed in the planet candidate catalog. We also newly identify planet candidate KOI 4351.01 as an eclipsing binary, and we report a secondary eclipse measurement for Kepler-4b (KOI 7.01) of ∼ 7.50 ppm at a phase of ∼ 0.7, indicating that the planet is on an eccentric orbit.

WASP-104b is Darker Than Charcoal

“…Typical visual geometric albedos of hot Jupiters are of the order of 0.1 (Schwartz & Cowan 2015) and are statistically lower than for hot super-Earths (Demory 2014) and Neptunes (Sheets & Deming 2017). According to the atmospheric models, the lower albedos may be attributed to the presence of alkali metals as well as TiO and VO in hotJupiter atmospheres, which causes significant absorption in the visual wavelengths (Demory et al 2011).…”

Aerosols in Exoplanet Atmospheres

“…Cooler planets observed at shorter wavelengths (Shporer & Hu, 2015) are much more likely to yield precise albedo measurements. Finally, the geometric albedos of hot and warm ( T eq ≥ 600 K) Neptune‐size, mini‐Neptune, and rocky exoplanets in the Kepler bandpass have been constrained to low values (≤0.2) (Demory, 2014; Jansen & Kipping, 2018; Sheets & Deming, 2014, 2017). Though the large measurement uncertainties have prevented solid conclusions to be drawn about aerosol properties in their atmospheres, reflective, spatially extensive aerosols are unlikely.…”

Multi-season optical modulation phased with the orbit of the super-Earth 55 Cancri e

“…However, 55 Cnc e should be compared to planets of its own size. Albedo measurements of the Kepler close-in super-Earth and Neptune sample as a whole have revealed that these worlds are somewhat less dark than hot Jupiters, but still have A g values generally below 0.3 (Demory 2014;Sheets & Deming 2017;Jansen & Kipping 2018). One exception is the hot rocky exoplanet Kepler-10b (Batalha et al 2011).…”