演題者：Renyu Hu (NASA JPL)
講演タイトル：Toward the Observational Studies of Exoplanet Habitability
6/28 (水) 13:30-14:30 @MISHIMA Hall ＆ Zoom（Zoom IDとパスワード情報についてアウトリーチ担当の冬月までsebastian.d_at_sophia.ac.jpまでご連絡ください。）
JWST provides revolutionary capabilities to measure the atmospheric compositions of small exoplanets and the possibility of near-term observational studies of exoplanet habitability. While the number of temperate and rocky exoplanets suitable for JWST characterization is limited, profound progress in understanding the diversity, occurrence rate, and formational conditions of habitable worlds will be made by observing temperate sub-Neptunes (planets with radii between 1.5 and 2.6 times Earth radius) as well as hotter rocky planets. A subset of temperate sub-Neptunes may support liquid-water oceans if they do not have massive H2 atmospheres and are thus not too hot at the bottom of the atmospheres. I will present a novel method to combine transmission spectroscopy and planetary chemistry modeling to determine if temperate sub-Neptunes are capped by thick H2 atmospheres. With a growing sample of temperate sub-Neptunes that straddle the runaway greenhouse limit, these observations may also provide a cornerstone for this foundational theory in planetary science. Hotter rocky planets, on the other hand, are suitable for observations in the thermal infrared and thus provide a testing ground for models of atmospheric evolution and retention. I will discuss using thermal emission spectra to determine the surface or atmospheric compositions in the context of a JWST survey of ~10 likely rocky planets. The deep characterization of temperate or rocky exoplanets will bring us new questions and usher in an era for understanding the workings of small exoplanets with combined observations and models.
Dr. Renyu Hu is an expert in the research of physical and chemical processes, evolution, radiative transfer, and remote sensing of planetary and exoplanetary atmospheres. Dr. Hu developed, from the first principles, a general-purpose photochemical and thermochemical model for exploring the diversity of exoplanets, which has led to a strategy to determine whether temperate sub-Neptunes have liquid-water oceans, the revelation of an O2-CO runaway state on M stars’ rocky planets, and the prediction of helium-atmosphere exoplanets. He also pioneered the method to detect minerals on bare-rock exoplanet surfaces. Dr. Hu’s research group leads multiple JWST programs to characterize small or temperate exoplanets and also plays a significant role in the debate on the climate and atmospheric evolution of early Mars. Dr. Hu contributes to the endeavor of finding Earth-like exoplanets in our interstellar neighborhood in both science and instrumentation. His atmosphere models are used to determine what we can learn about terrestrial exoplanets from direct-imaging observations, and he has been providing project science leadership to NASA’s Starshade Technology Development to TRL-5 (S5) activity.