Characterizing Rocky and Gaseous Exoplanets with 2-meter Class Space-based Coronagraphs: General Considerations
Robinson et al
Several concepts now exist for small, space-based missions to directly characterize exoplanets in reflected light. Here, we develop an instrument noise model suitable for studying the spectral characterization potential of a coronagraph-equipped, space-based telescope. We adopt a baseline set of telescope and instrument parameters, including a 2 m diameter primary aperture, an operational wavelength range of 0.4-1.0 um, and an instrument spectral resolution of 70, and apply our baseline model to a variety of spectral models of different planet types, including Earth twins, Jupiter twins, and warm and cool Jupiters and Neptunes. With our exoplanet spectral models, we explore wavelength-dependent planet-star flux ratios for main sequence stars of various effective temperatures, and discuss how coronagraph inner and outer working angle constraints will influence the potential to study different types of planets. For planets most favorable to spectroscopic characterization---cool Jupiters and Neptunes as well as nearby Earth twins and super-Earths---we study the integration times required to achieve moderate signal-to-noise ratio spectra. We also explore the sensitivity of the integration times required to detect the base of key absorption bands (for methane, water vapor, and molecular oxygen) to coronagraph raw contrast performance, exozodiacal light levels, and the distance to the planetary system. Most modeled observations have noise dominated by dark current, indicating that improving CCD performance could substantially drive down requisite integration times. Finally, we briefly discuss the extension of our models to a more distant future Large UV-Optical-InfraRed (LUVOIR) mission.