Discriminating Between Cloudy, Hazy and Clearsky Exoplanets Using Refraction

TL;DR

This paper introduces a rapid method using refracted light observations to distinguish between cloudy, hazy, and clear exoplanet atmospheres, aiding in selecting optimal targets for detailed study.

Contribution

The authors propose a novel technique leveraging broadband refracted light measurements to identify cloud- and haze-free exoplanets efficiently.

Findings

Refracted light detection can be achieved in <10 hours with JWST for Jovian planets.

The method is most effective for planets with temperatures between 200-500 K.

Detection of refracted light indicates a clear atmosphere, ideal for further characterization.

Abstract

We propose a method to distinguish between cloudy, hazy and clearsky (free of clouds and hazes) exoplanet atmospheres that could be applicable to upcoming large aperture space and ground-based telescopes such as the James Webb Space Telescope (JWST) and the European Extremely Large Telescope (E-ELT). These facilities will be powerful tools for characterizing transiting exoplanets, but only after a considerable amount of telescope time is devoted to a single planet. A technique that could provide a relatively rapid means of identifying haze-free targets (which may be more valuable targets for characterization) could potentially increase the science return for these telescopes. Our proposed method utilizes broadband observations of refracted light in the out-of-transit spectrum. Light refracted through an exoplanet atmosphere can lead to an increase of flux prior to ingress and subsequent to egress. Because this light is transmitted at pressures greater than those for typical cloud and haze layers, the detection of refracted light could indicate a cloud- or haze-free atmosphere. A detection of refracted light could be accomplished in <10 hours for Jovian exoplanets with JWST and <5 hours for Super-Earths/Mini-Neptunes with E-ELT. We find that this technique is most effective for planets with equilibrium temperatures between 200 and 500 K, which may include potentially habitable planets. A detection of refracted light for a potentially habitable planet would strongly suggest the planet was free of a global cloud or haze layer, and therefore a promising candidate for follow-up observations.