Ejecta, rings and dust in SN 1987A with JWST MIRI/MRS

Supernova (SN) 1987A is the nearest supernova explosion in $\sim$400 years. Using the superb sensitivity and angular resolution of the {\em JWST} MIRI Medium Resolution Spectrograph, we have spatially resolved the ejecta, equatorial ring (ER) and outer rings in the mid-infrared 12,927 days ($\sim$35 years) after the explosion. The spectra are rich in line and dust continuum emission, both in the ejecta and the ring. Hydrogen recombination line emission, from dense clumps of gas in the ring, is more compact compared to the dust emission. Broad emission lines (280-380~km~s$^{-1}$ FWHM) seen from all singly ionized species originate from the expanding ER, with properties consistent with dense post-shock cooling gas. Narrower emission lines (100-170~km~s$^{-1}$ FWHM) seen from highly ionized species originate from a more extended lower-density component whose higher degree of ionization may have been produced either by radiation from the shocks progressing through the ER, or by the UV radiation pulse associated with the original supernova event. The asymmetric east-west dust emission in the ER has continued to fade, with constant temperature, signifying a reduction in dust mass. Small grains in the ER are preferentially destroyed, with larger grains from the progenitor surviving the transition from SN into SNR. The ER is fit with a single set of optical constants, eliminating the need for a secondary featureless hot dust component spatially coexisting with the silicates. We find several broad emission lines from [Ne~{\sc ii}], [Ar~{\sc ii}], [Fe~{\sc ii}], and [Ni~{\sc ii}] from the ejecta. With the exception of the [Fe~{\sc ii}]~25.99$\mu$m line, these all originate from the ejecta close to the ring, and being excited by X-rays from the interaction. The [Fe~{\sc ii}] ~5.34$\mu$m to 25.99$\mu$m line ratio indicates a temperature of only a few hundred K in the inner core, consistent with being powered by ${}^{44}$Ti decay.