Cleaning Our Hazy and Cloudy Lens on sub-Neptune Exoplanets

Relatively little is understood about the atmospheric composition of middling size exoplanets, sub-Neptunes. Although being one of the most common planets observed [1], a subclass of these exoplanets have long eluded atmospheric characterization for their uncharacteristically flat spectra observed from the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) near-infrared 1.1-1.7 μm, grism G141. Their flattened spectra are likely due to planet-wide photochemical haze and clouds. Following Crossfields and Kriedberg [2], we use a water amplitude metric in which to measure the haziness/cloudiness of these exoplanets. We endeavor to expand upon their work and methodology by increasing the sample size and exploring and understanding new possible trends between planetary haziness and planetary or stellar parameters. We’ve added four more planets, K2-18 b, Kepler 51 b, Kepler 51 d, HD 106315 c. Our analysis shows that K2-18 b breaks the trend between the water amplitude and equilibrium temperature of the exoplanets, which indicates that exoplanet haziness may not be a simple function of one planetary parameter. Instead, we believe that multiple planetary parameters could be affecting haziness, as demonstrated by recent laboratory experiments [3] and theoretical modeling results [4]. Future work is to continue exploring trends involving other planetary parameters such as planetary radiation environments (NUV//FUV/EUV fluxes), star age, metallicity with the aid of laboratory and theoretical modeling results. [1] Fressin, F., et al., 2013, ApJ, 766, 81 [2] Crossfield, I. J. M. & Kreidberg, L, 2017, AJ, 154, 261 [3] Yu, X., et al., In prep [4] Gao, P. & Zhang X., 2020, ApJ, 890, 93