DIX Planetary Science Seminar

JWST provides a unique opportunity to spectroscopically characterize the surface compositions of terrestrial exoplanets for the first time. Close-in, rocky planets orbiting M dwarfs are ideal targets for these studies, and recent Spitzer and JWST measurements have shown that many have little to no atmosphere. There are currently six hot rocky exoplanets, including LHS 3844 b, with approved JWST programs to measure their thermal emission spectra with MIRI LRS. Current models for the bare-rock spectra of these planets utilize a spectral library spanning a limited number of surface types. This library was also measured at room temperature, and does not capture temperature-dependent changes in spectral feature shapes. Here we present a new spectral library that includes a larger variety of rock types with varying textures (solid slab, coarsely crushed, and fine powder), as well as high temperature (up to 830 K) emissivity measurements for select samples. We use this new library to highlight the importance of spectroscopically resolved measurements for constraining the surface compositions of hot, rocky exoplanets.

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Close-in exoplanets undergo intense radiation from their host stars, driving atmospheric escape that can catastrophically alter the planets' evolution. The majority of atmospheric escape observations are for systems with K star hosts, as these stars optimally populate metastable helium, a ground-accessible tracer of atmospheric loss. While most of these outflows are narrowly confined, the first two detections of atmospheric escape on planets orbiting F stars reveal much faster outflows that extend far beyond the planet's Roche Lobe. Such detections are surprising, and hint at the possible presence of additional energy sources (e.g., Balmer-driven escape) that can drive outflows for planets orbiting hot stars. We recently initiated the first dedicated mass loss survey of planets orbiting F stars in order to determine whether these first two detections are representative of the broader population, and to test competing models for the origin of the fast observed outflow rates. We report detections of outflows for four additional planets orbiting F stars, all of which are significantly smaller than prior published detections despite being nearly analogous systems. We explore potential explanations for the different outflow behaviors, including the role of stellar rotational velocity and XUV flux in setting outflow rates.