UCLA

Atmospheric mass loss plays a central role in planetary evolution, shaping the observed distribution of radii and compositions. This dissertation investigates escape mechanisms across multiple evolutionary stages using complementary observational strategies. First, I use high-precision radial velocity measurements from Gemini-N/MAROON-X to constrain the masses of super-Earths and sub-Neptunes in the disordered TOI-1266 system. These measurements test predictions from photoevaporation and core-powered mass loss models. Second, I detect ongoing atmospheric escape from the mature hot Jupiter WASP-69b using high-resolution near-infrared transmission spectroscopy from Keck/NIRSPEC. He I 10830 Å absorption is consistent with a comet-like tail extending at least seven planetary radii, shaped by stellar wind. The inferred mass-loss rate is approximately 1~$M_{\oplus}$~Gyr$^{-1}$. Finally, I search for extreme real-time escape from the young (15–25 Myr) sub-Saturn planets V1298 Tau c and d using Keck/NIRSPEC. I report upper limits on mass-loss rates for both planets. Together, these studies provide a multi-angle approach of studying atmospheric escape and investigating how planetary atmospheres evolve over both long and short timescales.