Xi Zhang received his Ph.D. in planetary sciences from California Institute of Technology in 2013. He is one of the few scientists whose research covers many subfields in planetary atmospheres, including remote sensing, fluid dynamics, chemistry, haze and cloud formation, and radiative transfer. Xi’s work revolutionized our understanding of the roles of aerosols in planetary atmospheres in many aspects. Xi’s proposal on the feedback of sulfur aerosols on gas chemistry is the leading theory to explain Venus Express’s observations of sulfur oxides. From Cassini data, Xi derived maps of temperature, chemical species, and aerosols in Jupiter’s stratosphere and identified the role of aerosols in the energy budget on Jupiter. Xi proposed an explanation for the unexpected cold atmosphere of Pluto observed by the New Horizons mission. He found out that hazes in Pluto’s atmosphere, instead of gases, dominate the radiative cooling as well as the heating. This discovery led to a paradigm shift in our understanding of the atmospheric energy balance of the new “cold and hazy” regime that also includes Neptune’s moon Triton and Saturn’s moon Titan. Xi’s work has implications for the haze and cloud formation on exoplanets and its impact on observed spectra and planetary evolution of low-mass planets, as well as on developing the next-generation three-dimensional general circulation models of the cloudy atmospheres on giant planets, exoplanets, and brown dwarfs. His contributions overall have been both wide and deep, revolutionizing our understanding of planetary climate.
—Yuk Yung, California Institute of Technology, Pasadena
