Meet the Fellows Research Searching for trends across the atmospheric conditions of diverse giant exoplanets to uncover their formation pathways. Host University University of California, Los Angeles Year Awarded 2025 Website Professional Page Jerry Xuan, Ph.D. Ph.D., Astronomy, California Institute of Technology Research Searching for trends across the atmospheric conditions of diverse giant exoplanets to uncover their formation pathways. Host University University of California, Los Angeles Year Awarded 2025 Website Professional Page “The Gliese 229 B system stretches our imagination and our theory as to how different planetary or stellar systems can be. It highlights that there are a lot of unknowns out there, so we should be ready for surprises.”Jerry Xuan, Ph.D.As a first-year undergraduate student, Jerry Xuan, Ph.D., helped assemble a prototype instrument that transmits light through narrow optical fibers to a spectrograph—a concept now central to the Keck Planet Imager and Characterizer (KPIC). Years later, he used KPIC data to study giant planets and their atmospheres. As KPIC’s successor, the High-resolution Infrared Spectrograph for Planet Characterization (HISPEC), prepares to come online, Dr. Xuan is coming full circle—using the next-generation instrument to unlock new planetary discoveries.Dr. Xuan specializes in detecting and characterizing directly imaged gas giant companions to understand whether they shape slowly as solid particles clump together to form a core and attract a gaseous atmosphere, or emerge rapidly as an imbalance of density causes a disk of gas and dust to collapse. His Ph.D. research focused on brown dwarf companions, massive bodies that blur the line between stars and planets. By analyzing their atmospheres, he found that brown dwarf companions almost always share their host star’s chemical makeup, suggesting that they form like stars rather than planets. He has also uncovered evidence that giant planets, in contrast to brown dwarfs, contain a higher proportion of metals than their stars. An illustration showing the twin brown dwarfs Gliese 229 Ba and Gliese 229 Bb orbiting closely around each other. Credit: K. Miller, R. Hurt (Caltech/IPAC) More recently, Dr. Xuan has been investigating whether certain gas giant companions are, in fact, binary systems—two astronomical objects that orbit each other due to their mutual gravity. His discovery that Gliese 229 B is not one brown dwarf, but two, solved a decades-old puzzle about its unexpected dimness and provided new evidence that brown dwarfs form through gravitational instability. To do this, he assembled one of the most comprehensive datasets ever collected on a single astronomical object. During his 51 Pegasi b Fellowship, Dr. Xuan will turn his focus to Jupiter and Saturn analogs. Using the Near-Infrared Spectrograph (NIRSpec) on the JWST to study key wavelength regions, along with next-generation instruments SCALES and HISPEC at the Keck Observatory, he will map the atmospheres of a large sample of gas giants orbiting their stars. Jerry is eager to see whether extrasolar gas giants resemble those in our own solar system—and whether more binary worlds are waiting to be found. Beyond research, he aims to pay forward the guidance that shaped his own path by mentoring others.Dr. Xuan received a Ph.D. in astronomy from the California Institute of Technology in Winter 2025.