Simulation of exoplanet spectra, particularly reflection spectra, is key to planning for and eventual interpretation of observations of directly imaged exoplanet spectra. We demonstrate the use of the Planetary Spectrum Generator (PSG) to produce simulations of reflected light exoplanet spectra. We use PSG to examine multiple issues relevant to the simulation of all directly imaged exoplanet spectra and to produce sample spectra of a promising direct imaging exoplanet target, Ups And d, with different assumptions regarding its atmosphere. Our simulations introduce a new, fast and accurate sub-sampling technique that enables calculation of accurate disk integrated spectra an order of magnitude faster than Chebyshev-Gauss sampling for moderate to high resolution sampling. Additionally, we demonstrate that the significant differences that exist in opacities of key molecules between some of the most well known databases can drive measurable and significant differences in simulated spectra for cloudless and (to a lesser extent) cloudy atmospheres.
We simulate spectra for Ups And d with different metallicity, cloud and haze properties and convolve the spectra with current Nancy Grace Roman Space Telescope spectral capabilities to demonstrate their detectability. The eccentric orbit of Ups And d results in an apastron distance that should enable Roman to observe the planet, and the simulated spectra suggests the planet may be a favorable target for detection and potentially characterization by Roman. Ups And d represents a unique class of planet, a Jupiter-size gas giant in the conventional habitable zone of its star. Using lessons from our solar system’s gas giants, our simulated spectra demonstrates that composition, the presence of clouds and hazes, condensate particle size and cloud position are all features of Ups And d that may be accessible to future direct imaging exoplanet characterization efforts.