Using the JWST MIRI coronagraphic filters F1065C, F1140C and F1550C, this work reports the first unambiguous mid-infrared detection of ammonia (NH3) near 10.5 micron in GJ 504 b, one of the coldest directly imaged planetary-mass companions (~500 K). By subtracting the stellar diffraction pattern with a reference-star image library and fitting Exo-REM atmospheric-model grids to combined near- and mid-infrared photometry, it measures the NH3 abundance and refines the companion's effective temperature and radius. Students learn how NH3 acts as a diagnostic molecule for the temperature and surface gravity of cold substellar atmospheres.
Ammonia (NH3) has a mid-infrared absorption feature near 10.5 micron that atmospheric models predict should be detectable in giant planets colder than about 1200 K. Using the JWST/MIRI coronagraphic …