A primary science goal of JWST is to understand the atmospheres of other worlds and investigate how a planet's atmospheric composition can inform us about its formation and evolutionary history. Of particular interest is the recently-discovered sample of short-period, Jupiter-sized planets orbiting M-dwarfs, which present challenges to our current theories of planet formation. This new sample of planets also represents an extreme regime of planet formation that has not yet been probed in the context of atmospheric characterization.
The path to understanding how these systems form therefore begins with a fundamental question: How do the atmospheres of these M-dwarf giant planets compare to giant planets orbiting Sun-like stars? Thanks to the large transit-depths and warm temperatures of M-dwarf giant planets, we can access the absorption features for both water and methane in the planet atmospheres. We therefore have the unique opportunity to observe this new sample of close-in giant planets orbiting M dwarfs with JWST to precisely characterize their atmospheric composition and metallicity, and compare them with their FGK host analogues.
With this JWST large program, we will obtain transmission spectra of seven M-dwarf short-period Jupiters using the NIRSpec/PRISM to observe between 0.6-5.3 µm, a region where molecular features from water and methane are dominant, which we will use as tracers for atmospheric metallicity. Ultimately, this study will shed light on whether M-dwarf gas giants have similar formation and evolution pathways to their FGK counterparts.