UC Santa Cruz

Planets both inside and beyond the solar system have different atmospheres, making them display various phenomena. With the increasing number of exoplanets detected, in particular with detailed observations taken by the advanced JWST nowadays, more samples are available to widen such diversity. One of the key challenges is to understand their atmospheric components and physical properties via remote sensing (like images, spectra, and lightcurves) rather than in-situ detection of probes, especially for these distant objects. So applying physical models could offer additional assistance in explaining currently limited data, as well as give some guidance for conducting future observations. Moreover, the Bayesian retrieval approach makes it possible to seek the most probable solutions in a high-dimension parameter space efficiently.

Chapter One describes two possible scenarios of Pluto's atmospheric haze, directly based on the temperature-pressure profile acquired by the New Horizons spacecraft. A radiative-conductive-conductive model was used to examine the energy balance of gases and haze individually, suggesting that an additional mechanism of eddy heat transport is essential in Pluto's lower atmosphere. An icy haze, 20 times smaller than Titan's tholins in opacity, is also proposed and will be determined by infrared observations of JWST.

Chapter Two further studies Pluto's haze by rotational emission lightcurves indirectly. The total outgoing thermal emission comes from not only Pluto's and Charon's surfaces as previously believed, but also Pluto's atmospheric haze as learned in Chapter One. A two-dimensional surface model of heat conduction is developed to estimate the surface parameters and flux contribution more accurately. After removing surfaces, the remaining total flux should come from Pluto's haze, which is significant in the mid-infrared but may be neglected in the far-infrared. Predictions at other mid-infrared wavelengths are then given in view of current haze knowledge. JWST MIRI works at these wavelengths to prove or constrain such haze.

Chapter Three jumps out of the solar system and pays attention to the sub-Neptune planets that are intermediate in size between Earth and Neptune. Helium enrichment due to preferential hydrogen escape is suggested for their thin atmospheric envelopes, which requires a method to obtain its helium amount correctly. Transmission spectra featured by the mechanism of collision-induced absorption are applied to retrievals for assessing how accurate it can be when future JWST data arrive. The results are optimistic in the helium-enhanced situation with 30 ppm errors.

In summary, this dissertation thesis consists of three projects exploring the physics of planetary atmospheres, two of which are constraining Pluto's haze opacity but from different aspects. The other one is loosely related to icy planets (like Pluto) and is mainly focused on the helium abundances in sub-Neptune's atmosphere. These projects cover the flux calculations of emission and transmission, along with the time or wavelength sequences, from the surface or atmosphere. The physical modeling method is applied as a bridge between the physical understanding of atmospheric components and current or future observations, in the era of JWST.