In order to understand a process as complex as planet formation, the most extreme cases are often the most revealing. At the hottest extreme of planet formation are the ultra-short-period planets (USP, orbital period ~1 day, <2 R_earth) which orbit their host stars just a few stellar radii away. Our uniform analysis of USPs revealed a prevalence of Earth-like rocky composition. The high mutual inclinations among USP planets also betray a dynamically hot formation scenario. Our upcoming JWST program will probe the surface mineralogy through phase curve variations on a 0.7 R_Earth USP. The “super-puffs” (planets with anomalously low density ~0.1 g cm^-3) are extremely susceptible to rapid hydrodynamic mass loss with a timescale that is much shorter than the system's age. Even more puzzling, super-puffs are estimated to have large scale heights of ~3000 km, yet recent observations revealed completely flat transmission spectra. I will introduce a scenario that may explain these observations of “super-puff”. Finally, we will describe a few novel methods of measuring the orbital tilt of a planet. We found a population of Neptune-sized planets on polar orbits that might have initially formed further out in the disk before they dynamically arrived at their current close-in, misaligned orbits. The heat generated in the migration might have triggered an episode of intense atmospheric loss that is seen in the metastable He observation.
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