The Intricacies of Using Color-Color Diagrams to Classify Directly Imaged Planets

Thursday 5 July, 16:30

Atmospheric characterization of directly imaged planets has thus far been limited to ground-based observations of young, self-luminous, Jovian planets. NASA, however, is currently in the planning phase for WFIRST and is investigating other direct imaging missions (HabEx, LUVOIR, OST). These missions will enable direct imaging of reflected light from cooler ($T_{eff} \sim$150-300 K) exoplanets located several AU from their host star. Because the proposed design of some of these missions include both photometry and spectroscopy, the idea of using planet-colors, in addition to spectroscopy, has been proposed as a mechanism to classify planet populations. Additionally, it has been suggested that Earth's reflection spectrum, dominated by the Rayleigh scattering in the blue and ozone absorption in the visible, is unique compared to other Solar System planets. Here, we investigate the intricacies of using colors to classify planets by analyzing a grid of 10,000 reflected light spectra spread across different metallicities, temperature-pressure profiles, cloud properties, and phase angles. We determine how correlated these planet parameters are with the colors in the WFIRST photometric bins and other photometric bins proposed in the literature. We also discuss to what extent, if any, planet populations can be disentangled from each other using a variety of statistical techniques (e.g. cloudy vs. cloud-free, high and low metallicites). Lastly, we analyze the reflected light spectrum of an Earth-like planet against our grid, and determine whether or not the pale blue dot does in fact remain unique.

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