  Thanks to mid-infrared observations, we provide new clues to the element
mixing during a supernova explosion by probing the mixing between three
adjacent layers: the oxygen burning products layer (sulfur, argon,...), the
silicate layer and the neon layer. The silicate and neon layers are both
contaminated by sulfur and argon in a macroscopic way, but appear segregated,
so that the mixing is heterogeneous. This finding complements the microscopic
mixing information deduced from presolar grains found in meteorites and implies
that, at present time, supernovae are probably not the main dust factory in the
Galaxy. The mixing is often interpreted in terms of hydrodynamical
instabilities driven by the outward shock following the implosion of the
supernova core. Testing whether such instabilities can lead to the injection of
material from a layer into upper layers without complete mixing, as suggested
by the observations presented in this paper, should be possible with the
intense lasers which are starting to be used to simulate astrophysical plasmas.
