Discriminating Between Cloudy, Hazy and Clearsky Exoplanets Using Refraction

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.

Accepted for publication in ApJ Letters

References in corpus (21)

• Habitable Zones Around Main-Sequence Stars: New Estimates
• Detection of an Extrasolar Planet Atmosphere
• The NextGen Model Atmosphere grid for $3000\le \Teff \le 10000\K$
• Characteristics of planetary candidates observed by Kepler, II: Analysis of the first four months of data
• Clouds in the atmosphere of the super-Earth exoplanet GJ 1214b
• Infrared Transmission Spectroscopy of the Exoplanets HD209458b and XO-1b Using the Wide Field Camera-3 on the Hubble Space Telescope
• Hubble Space Telescope Transmission Spectroscopy of the Exoplanet HD 189733b: High-altitude atmospheric haze in the optical and near-UV with STIS
• A featureless transmission spectrum for the Neptune-mass exoplanet GJ 436b
• How to Distinguish between Cloudy Mini-Neptunes and Water/Volatile-Dominated Super-Earths
• Discovery and Characterization of Transiting SuperEarths Using an All-Sky Transit Survey and Follow-up by the James Webb Space Telescope
• HST hot Jupiter transmission spectral survey: evidence for aerosols and lack of TiO in the atmosphere of WASP-12b
• Identification of Absorption Features in an Extrasolar Planet Atmosphere
• Feasibility Studies for the Detection of $O_2$ in an Earth-like Exoplanet
• TiO and VO broad band absorption features in the optical spectrum of the atmosphere of the hot-Jupiter HD209458b
• Impact of atmospheric refraction: How deeply can we probe exo-Earth's atmospheres during primary eclipse observations?
• Glancing views of the Earth. From a lunar eclipse to an exoplanetary transit
• Using Dimers to Measure Biosignatures and Atmospheric Pressure for Terrestrial Exoplanets
• The Effects of Refraction on Transit Transmission Spectroscopy: Application to Earth-like Exoplanets
• Spectral features of Earth-like planets and their detectability at different orbital distances around F, G, and K-type stars
• Transmission spectrum of Venus as a transiting exoplanet
• The June 2012 transit of Venus. Framework for interpretation of observations

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• The Habitability of Proxima Centauri b: II: Environmental States and Observational Discriminants
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• Refraction in planetary atmospheres: improved analytical expressions and comparison with a new ray-tracing algorithm
• Effects of refraction on transmission spectra of gas giants: decrease of the Rayleigh scattering slope and breaking of retrieval degeneracies
• How to Characterize the Atmosphere of a Transiting Exoplanet
• Exoplanet phase curves at large phase angles. Diagnostics for extended hazy atmospheres
• Out-of-Transit Refracted Light in the Atmospheres of Transiting and Non-Transiting Exoplanets
• Refraction in exoplanet atmospheres: Photometric signatures, implications for transmission spectroscopy, and search in Kepler data
• Influence of Biomass Emissions upon Habitability, Biosignatures and Detectability in Earth-like Atmospheres