Forty years ago it was proposed that gas phase organic chemistry in the interstellar medium can be initiated by the methyl cation CH3+ (1–3), but hitherto it has not been observed outside the Solar System (4, 5). Alternative routes involving processes on grain surfaces have been invoked (6, 7). Here we report JWST observations of $${{\rm{CH}}}_{3}^{+}$$ in a protoplanetary disk in the Orion star forming region. We find that gas-phase organic chemistry is activated by UV irradiation.
