Diverse Clouds and Hazes in Planetary Atmospheres

Tuesday September 21st at 15:00-16:00 UTC
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Abstract

Clouds and hazes are ubiquitous in all substantial atmospheres in the Solar System. Abundant particles are also inferred from observations in hotter atmospheres of exoplanets and brown dwarfs. Exotic clouds in extraterrestrial atmospheres could result from condensation of water, ammonia, sulfuric acid, salts, silicates, metals, and/or nitriles and hydrocarbons produced by atmospheric chemistry upon UV radiation and high-energy particles. In this talk I plan to showcase several examples we have studied recently to elaborate significant roles of clouds and hazes on the energy budget, thermal structure, chemistry and dynamical circulation in planetary atmospheres. I will first start from our sister planet Venus and talk about sulfur chemistry and formation of sulfuric acid clouds. I will use a simple cloud model to demonstrate the critical role of binary condensation in the sulfur acid formation and its impact on gas species such as sulfuric oxides and water vapor. I will then talk about the thin, cold and hazy atmospheres in the outer Solar System. Using Titan, Triton and Pluto as examples, I will show how these atmospheres regulate themselves such that the chemically produced hydrocarbon haze/ice particles significantly dominate the radiative energy balance over the gas volatiles. In particular, the particles could explain the colder-than-expected temperature on Pluto observed by the New Horizons mission. Lastly, I would like to talk about clouds in hydrogen-dominated atmospheres such as Jupiter, hot Jupiters and brown dwarfs, highlighting the importance of clouds on the interpretation of the observed spectra and light curves and the impacts of cloud radiative feedback and moist convection on the atmospheric circulation on those bodies. Specifically, I will talk about how could clouds help us to understand some recent puzzles on Jupiter’s atmosphere observed from the Juno mission.

Dr. Xi Zhang is an associate professor in the Department of Earth and Planetary Sciences at University of California Santa Cruz. He got his bachelor degree in space science from Peking University in 2007 and received the Ph.D. degree in planetary sciences from California Institute of Technology in 2013. Then he spent two years in University of Arizona as a postdoc and started his faculty position since 2015 at UC Santa Cruz. Xi’s research covers many topics in planetary atmospheres within and out of the Solar System. He has been awarded by the AGU Ronald Greeley Early Career Award in 2019.