Diagnosing Clouds and Hazes in Exoplanet Atmospheres
Fraine, Jonathan David
Deming, Leo D
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Exoplanet atmospheres provide a probe into the conditions on alien worlds, from hot Jupiters to Super-Earths. We can now glimpse the behaviour of extreme solar systems that defy our understanding of planet formation and capture our imaginations about the possibilities for understanding planets and life in our universe. I combined multi-epoch, multi-instrument observations from both space and ground based facilities. I developed observational techniques and tools to constrain exoplanetary atmospheric compositions, temperature profiles, and scale heights over a span of planetary masses and wavelengths, that provided a probe into the properties of these diverse planetary atmospheres. I led a team that used the Spitzer Space Telescope, with the IR Array Camera (IRAC), to observe the well known transiting Super-Earth, GJ 1214b (~2.7 R_Earth). My precisely constrained infrared transit depth, error ~ O(40 ppm), significantly constrained the lack of any molecular detections out to a wavelength of 5 microns. The significance of this null detection challenges self-consistent models for the atmosphere of this super-Earth. Models must invoke thick, grey opacity clouds that uniformly cause the atmosphere to be opaque at all wavelengths. My team and I used the Hubble Space Telescope Wide Field Camera 3 (HST-WFC3) to spectroscopically probe the atmosphere of the transiting warm Neptune, HAT-P-11b (~4.5 R_Earth), and detected the first molecular signature from a small exoplanet (R_planet < R_Saturn), inferring the presence of a hydrogen rich atmosphere. The average densities of many transiting exoplanets are known, but the degree to which atmospheric composition -- abundance of Hydrogen relative to other atoms and molecules -- correlates with the bulk composition has not yet been established. In an effort to characterize the atmospheric metallicity in greater detail, my team observed HAT-P-11 using warm Spitzer IRAC at 3.6 and 4.5 microns. The non-detections of eclipses HAT-P-11b provided upper limits on the temperature profile at 3.6 and 4.5 microns. I am one of the founding members of the ACCESS collaboration (Arizona-CfA-Catolica Exoplanet Spectroscopy Survey), a ground based observational campaign to spectroscopically survey a catalogue of exoplanetary atmospheres using major optical telescopes. I observed several of our targets from the 6.5m Magellan-Baade telescope. The results of my first observation provided low signal-to-noise constraints on the cloud properties of the hot Jupiter WASP-4b, as well as the UV radiation environment produced by its host star, WASP-4. The combination of these observational constraints provided greater insight into the end-products of the planet formation process, and developed the knowledge base of our community for both cloudy and clear worlds.