地点：教学行政楼1514
时间：2014年7月7日上午10：00
报告人：Xi Zhang 
单位：University of Arizona
摘要：It wasn’t until mid-1990s that the first planet outside the solar system as well as the first brown dwarf, an intermediate object between planet and star, were discovered. In the past twenty years, the research of those two kinds of objects has experienced a spectacular series of observational breakthroughs. We now know, most of these bodies have atmospheres, but with strange behaviors different from anything encountered on Earth or other planets in the Solar System. That challenges our current understanding of how atmosphere works. As the number of alien worlds increases, more strange behaviors are expected. Two examples are provided here.

There exists one kind of exoplanet called the “super-earth”. Depending on the metallicity of the protoplanetary disk, the details of planetary formation and planetary evolution, the atmospheres of exoplanets could exhibit a variety of bulk compositions. Examples include hydrogen-dominated atmospheres like Jupiter, more metal-rich atmospheres like Neptune, evaporated atmospheres dominated by helium in analogy to helium white dwarfs, or carbon dioxide, water vapour, nitrogen, and other heavy molecules as exhibited by terrestrial planets in the solar system. What are the effects of bulk composition on the atmospheric dynamics on the exoplanets? Despite differing opacities that will impact the radiative energy deposition, differing bulk compositions also differ in molecular weight and specific heat. The latter two fundamental parameters might have crucial effects on various aspects of atmospheric structure and dynamics. 

In the second half, I would like to talk about the atmospheres on brown dwarfs, which are as interesting as exoplanets. Under the conditions of fast rotation, strong radiative dissipation and no external stellar flux, brown dwarfs occupy a unique corner of the parameter space of atmospheric dynamics theories. Do the atmospheres of the brown dwarfs exhibit east-west jets pattern as exist on both the gas giants in our solar system and the close-in extra-solar giant planets, or are they dominated by isotropic turbulence and vortices instead? My recent work is mainly driven by those questions as well as some quite puzzling observations on brown dwarfs.

The slides will be in English, but the talk will be given in Chinese.