2025NatAs...9.1680W

Debris disks are exosystems thought to arise from collisions among planetesimals. Despite being dust dominated, ALMA has detected reservoirs of CO gas in some debris disks. The origin of this gas is debated, as it could be primordial H ₂ -dominated gas from the parent protoplanetary disk, or it could be released by volatile-rich minor bodies. Here we report JWST/NIRSpec observations of the 49 Ceti debris disk that spatially resolve ro-vibrational CO emission. The CO spectra can be explained by fluorescent excitation from ultraviolet and infrared stellar photons. We show that this technique of resolving fluorescently excited CO is sensitive to small CO masses that could go undetected by ALMA. We compare the CO excitation temperatures derived from our model fitting of the JWST spectra to predictions for an H ₂ -rich and secondary gas model for the system and find that our results do not appear consistent with the H ₂ -rich gas model. Resolving fluorescently excited CO emission opens a door for probing the nature of gas in debris disks and determining if it is long-lived primordial gas or if it is released from volatile-rich minor bodies.