The discovery of argon in comet C/1995 O1 (Hale-Bopp)

On 1997 March 30.14, we observed the EUV spectrum of the bright comet C/199 5 O1 (Hale-Bopp) at the time of its perihelion, using our Extreme Ultraviol et Spectrograph sounding-rocket telescope/spectrometer. The spectra reveal the presence H Ly beta, O+, and, most notably, argon. Modeling of the retri eved Ar production rates indicates that comet Hale-Bopp is enriched in Ar r elative to cosmogonic expectations. This in turn indicates that Hale-Bopp's deep interior has never been exposed to the 35-40 K temperatures necessary to deplete the comet's primordial argon supply.