Cleaning our Hazy Lens: Statistical Trends in Transmission Spectra of Warm Exoplanets
Physical and Biological Sciences
Department of Physics; Senior Thesis, PHYS 195A,B
Relatively little is understood about the atmospheric composition of temperate to warm out-of-our solar system planets (exoplanets), as many of them are found to have unexpectedly flat light-spectra (with little to no absorption features) from the star light that has passed through their atmospheres. This spectrum is called the transmission spectra. Their flattened spectra are likely due to atmospheric effects such as planet-wide hazes and clouds. We compile the transmission spectra of 23 warm exoplanets previously observed by the Hubble Space Telescope and quantify the haziness of each exoplanet using a normalized amplitude of the water absorption feature, the water amplitude. By examining the relationships between the water amplitude and various planetary and stellar forcing parameters, we endeavor to find trends of haziness associated with planetary properties. Our analysis shows that the previously identified linear trends between water amplitude and temperature or hydrogen-helium atmospheric mass fraction break down with the addition of new exoplanet data. Among all the parameters we investigated, the characteristic atmospheric height, planet gravity, and planet density hold the most statistically significant linear trends with the water amplitude. We also tentatively identified positive correlations for the orbital eccentricity and the age of the stars with the water amplitude Specifically, lower characteristic atmospheric height, higher planet gravity, density, orbital eccentricity, or the age of the star lead to clearer atmospheres. However, none of the parameters show very strong linear trends with the water amplitude, suggesting that haziness in warm exoplanets is not simply controlled by any single planetary/stellar parameter. Additional observations and laboratory experiments are needed to fully understand the complex physical and chemical processes that lead to the hazy/cloudy atmospheres in warm exoplanets.
