James Webb Space Telescope Feed Post

Arxiv: JWST COMPASS: The first near- to mid-infrared transmission spectrum of the hot super-Earth L 168-9 b Published: 11/5/2024 4:55:32 PM Updated: 11/5/2024 4:55:32 PM

Paper abstract: We present the first broadband near- to mid-infrared (3-12 microns)transmission spectrum of the highly-irradiated (T_eq = 981 K) M dwarf rockyplanet L 168-9 b (TOI-134 b) observed with the NIRSpec and MIRI instrumentsaboard JWST. We measure the near-infrared transit depths to a combined medianprecision of 20 ppm across the three visits in 54 spectroscopic channels withuniform widths of 60 pixels (~0.2 microns wide; R~100), and the mid-infraredtransit depths to 61 ppm median precision in 48 wavelength bins (~0.15 micronswide; R~50). We compare the transmission spectrum of L 168-9 b to a grid of 1Dthermochemical equilibrium forward models, and rule out atmosphericmetallicities of less than 100x solar (mean molecular weights <4 g mol^{-1})to 3-sigma confidence assuming high surface pressure (>1 bar), cloudlessatmospheres. Based on photoevaporation models for L 168-9 b with initialatmospheric mass fractions ranging from 2-100%, we find that this planet couldnot have retained a primordial H/He atmosphere beyond the first 200 Myr of itslifetime. Follow-up MIRI eclipse observations at 15 microns could make itpossible to confidently identify a CO2-dominated atmosphere on this planet ifone exists.