Explosion calculations of SN 1987A generate pictures of Rayleigh-Taylor fingers of radioactive 56Ni (56Ni → 56Co → 56Fe) which are boosted to velocities of several thousand km s−1. From the KAO observations of the mid-IR iron lines, a picture of the iron in the ejecta emerges which is consistent with the ‘frothy iron fingers’ having expanded to fill about 50% of the metal-rich volume of the ejecta (vm ≤ 2500 km s−1). The ratio of the nickel line intensities I([Ni I]7.5µm)/I([Ni II]6.6µm) yields a high ionization fraction of xNi 0.9 in the volume associated with the iron-group elements at day 415, before dust condenses in the ejecta.

From the KAO observations of the dust's thermal emission (2 µm − 100 µm), it is deduced that when the grains condense their infrared radiation is trapped, their apparent opacity is gray, and they have a surface area filling factor of about 50%. The dust emission from SN 1987A is featureless: no 9.7 µm silicate feature, nor PAH features, nor dust emission features of any kind are seen at any time. The total dust opacity increases with time even though the surface area filling factor and the dust/gas ratio remain constant. This suggests that the dust forms along coherent structures which can maintain their radial line-of-sight opacities, i.e., along fat ringers. The coincidence of the filling factor of the dust and the filling factor of the iron strongly suggests that the dust condenses within the iron, and therefore the dust is iron-rich.