Detection of Carbon Monoxide’s 4.6 Micron Fundamental Band Structure in WASP-39b’s Atmosphere with JWST NIRSpec G395H

Carbon monoxide (CO) is predicted to be the dominant carbon-bearing molecule in giant planet atmospheres, and, along with water, important for discerning oxygen and therefore carbon-to-oxygen ratio of these planets. The fundamental absorption mode CO has a broad double-branched structure composed many individual lines from 4.3 5.1 $\mathrm{\mu}$m, which can now spectroscopically measured JWST. Here we present technique detecting rotational sub-band at medium resolution NIRSpec G395H instrument. We use single transit observation hot Jupiter WASP-39b JWST Transiting Exoplanet Community Early Release Science (JTEC ERS) program native instrument ($R \,{\sim} 2700$) resolve structure. robustly detect by CO, an increase depth 264 $\pm$ 68 ppm, agreement contribution best-fit model low resolution. This detection confirms our theoretical expectations that WASP-39b's atmosphere, further supports conclusions C/O super-solar metallicities presented JTEC ERS papers WASP-39b.