The Direct Detectability of Giant Exoplanets in the Optical

Abstract

Motivated by the possibility that a coronagraph will be put on WFIRST/AFTA, we explore the direct detectability of extrasolar giant planets (EGPs) in the optical. We quantify a planet's detectability by the fraction of its orbit for which it is in an observable configuration ($f_{\mathrm{obs}}$). Using a suite of Monte Carlo experiments, we study the dependence of $f_{\mathrm{obs}}$ upon the inner working angle (IWA) and minimum achievable contrast ($C_{\min }$) of the direct-imaging observatory; the planet's phase function, geometric albedo, single-scattering albedo, radius, and distance from Earth; and the semi-major axis distribution of EGPs. We calculate phase functions for a given geometric or single-scattering albedo, assuming various scattering mechanisms. We find that the Lambertian phase function can predict significantly larger $f_{\mathrm{obs}}$'s with respect to the more realistic Rayleigh phase function. For observations made with WFIRST/AFTA's baseline capabilities ($C_{\min }\sim 10^{-9}$, $\mathrm{IWA}\sim 0.2^{\prime \prime }$), Jupiter-like planets orbiting stars within 10, 30, and 50 parsecs of Earth have volume-averaged observability fractions of $\sim$12%, 3%, and 0.5%, respectively. At 10 parsecs, such observations yield $f_{\mathrm{obs}}>1\%$ for low- to modest-eccentricity planets with semi-major axes in the range $\sim 2-10$ AU. If $C_{\min }=10^{-10}$, this range extends to $\sim 35$ AU. We find that, in all but the most optimistic configurations, the probability for detection in a blind search is low ($<5\%$). However, with orbital parameter constraints from long-term radial-velocity campaigns and Gaia astrometry, the tools we develop in this work can be used to determine both the most promising systems to target and when to observe them.

16 pages, 16 figures. Accepted for publication in ApJ

References in corpus (11)

• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• Wide-Field InfrarRed Survey Telescope-Astrophysics Focused Telescope Assets WFIRST-AFTA 2015 Report
• The Occurrence and Mass Distribution of Close-in Super-Earths, Neptunes, and Jupiters
• One or more bound planets per Milky Way star from microlensing observations
• On the Luminosity of Young Jupiters
• Astrometric exoplanet detection with Gaia
• Atomic and Molecular Opacities for Brown Dwarf and Giant Planet Atmospheres
• Synthetic Spectra and Colors of Young Giant Planet Atmospheres: Effects of Initial Conditions and Atmospheric Metallicity
• A Statistical Analysis of SEEDS and Other High-Contrast Exoplanet Surveys: Massive Planets or Low-Mass Brown Dwarfs?
• A grid of polarization models for Rayleigh scattering planetary atmospheres
• True Masses of Radial-Velocity Exoplanets

Cited by in corpus (13)

• Observations of Exoplanet Atmospheres
• Characterizing Earth Analogs in Reflected Light: Atmospheric Retrieval Studies for Future Space Telescopes
• Characterizing Rocky and Gaseous Exoplanets with 2-meter Class Space-based Coronagraphs
• Developing Atmospheric Retrieval Methods for Direct Imaging Spectroscopy of Gas Giants in Reflected Light I: Methane Abundances and Basic Cloud Properties
• Jupiter's Phase Variations from Cassini: a testbed for future direct-imaging missions
• Characterization of Exoplanet Atmospheres with the Optical Coronagraph on WFIRST
• Catalogue of exoplanets accessible in reflected starlight to the Nancy Grace Roman Space Telescope. A population study and prospects for phase-curve measurements
• Directly imaged exoplanets in reflected starlight. The importance of knowing the planet radius
• Prospects for Directly Imaging Young Giant Planets at Optical Wavelengths
• Unveiling non-gray surface of cloudy exoplanets: the influence of wavelength-dependent surface albedo and cloud scattering properties on retrieval solutions
• Laboratory Demonstration of Spatial Linear Dark Field Control For Imaging Extrasolar Planets in Reflected Light
• Breaking the Mass Inclination Degeneracy of Radial Velocity Measurements via Monitoring von Zeipel-Lidov-Kozai Cycles: Implications in the HD 41004 System
• Special cases : moons, rings, comets, trojans