Detection of visible light from the darkest world

TL;DR

This paper reports the detection of the faintest orbital phase variation in visible light from the exoplanet TrES-2b, revealing its extremely low albedo and significant emission, using Kepler data analysis.

Contribution

First detection of visible light from the darkest known exoplanet, demonstrating robust measurement of its low day-night contrast and implications for its atmospheric properties.

Findings

Detected a 6.5 ppm day-night contrast with 3.7 sigma confidence

Estimated geometric albedo of approximately 0.0253, indicating a very dark planet

Models suggest significant emission and low optical albedo, with moderate heat redistribution

Abstract

We present the detection of visible light from the planet TrES-2b, the darkest exoplanet currently known. By analysis of the orbital photometry from publicly available Kepler data (0.4-0.9 microns), we determine a day-night contrast amplitude of (6.5 +/- 1.9 ppm), constituting the lowest amplitude orbital phase variation discovered. The signal is detected to 3.7 sigma confidence and persists in six different methods of modelling the data and thus appears robust. In contrast, we are unable to detect ellipsoidal variations or beaming effects, but we do provide confidence intervals for these terms. If the day-night contrast is interpreted as being due to scattering, it corresponds to a geometric albedo of Ag = 0.0253 +/- 0.0072. However, our models indicate that there is a significant emission component to day-side brightness, and the true albedo is even lower (<1%). By combining our measurement with Spitzer and ground-based data, we show that a model with moderate redistribution (Pn ~ 0.3) and moderate extra optical opacity (kappa' ~ 0.3-0.4) provide a compatible explanation to the data.