Abstract:
Ever since the Nobel-prize-winning discovery (in 1995) of the first extra-solar planet (exoplanet) orbiting a Sun-like star, more exoplanets are being more rapidly discovered now. With knowledge of masses and radii of exoplanets, their densities can be estimated --- some agree with a rocky density (rocky worlds), some agree with a gas density (hot Jupiters), and some agree with a density of water-rock mixture (ocean worlds or sub-Neptunes). These new discoveries rekindle interests in habitability of other worlds and biosignatures therein. The goal of this talk is threefold: (1) introduce this exoplanetary revolution to a geoscience audience; (2) overview the findings so far in the astrophysics community; (3) highlight a special type of exoplanets --- ocean worlds or water worlds, and discuss the highly controversial planet K2-18b on which biosignatures like dimethyl sulfide (DMS) are claimed to be detected.

Biography:
Dr. Meng Tian is a Staff Scientist (junior group leader) at University Observatory Munich of Ludwig-Maximilians-Universität München (LMU), Germany. He obtained his Ph.D. from Department of Earth and Planetary Sciences of Yale University in 2016, and holds a B.Sc. in Geochemistry from Peking University. He applies fundamental physics and math principles to the study of a broad range of topics in Earth and planetary sciences, including magma dynamics, deep carbon transport, volcanic outgassing, and ocean chemistry during Snowball Earth. Recently, he embarked on exoplanet studies in an effort to translate our understanding of the Earth to the understanding of planets beyond our Solar System. He published works in geosciences, planetary sciences, and astrophysics, served on the James Webb Space Telescope time allocation committee (Cycle 3), and has been (co)conveners for sessions of major conferences like AGU and EGU. His research aims at bridging the gap between geosciences and astrophysics.