Left: MRS image of the CO₂ 15 μm band toward NGC 1333 IRAS4B showing the peak emission to be ~1000 au (~4″) offset from the source itself, whose position from millimeter interferometry is indicated by the white star. The beam size is indicated in the lower left corner. Right: MIRI-MRS spectrum of the NGC 1333 IRAS4B jet “knot” position in the 13-15 μm range highlighting its rich spectrum including hot C₂H₂ (600 K). For comparison, the spectrum of the high-mass protostar IRAS 23385, which shows only cold C₂H₂, is presented (Francis et al. 2024). The model spectra at the bottom show the contributions from C₂H₂ (100 and 600 K) and H₂O (280 K) in this wavelength range.