Allende Presolar Grains

Presolar grains are tiny dust particles that formed around another star. These grains were incorporated into the matrix of the carbonaceous chondrites.
The presolar grains formed from the cooling gas in the outflows of stars such as red giants,and in supernova explosions. They were part of the interstellar medium before becoming part of the cloud of gas and dust from which the Sun, Earth and planets formed. They are important clues to the processes by which the elements are formed in stars, as well as to the formation of our solar system. How these grains survived for us to find them in meteorites is a mystery. The unique mixtures of isotopes in these grains were first noticed in chemical analyses of large samples of carbonaceous chondrite meteorites. The search for the material carrying these isotopic signatures led to the isolation of presolar grains from their meteorite host by dissolving the host rock with acids. The extremely unusual mixture of the isotopes of xenon suggest that these grains originated in supernova explosions.
Presolar grains of a few types have been isolated. Nanometer scale diamonds are must abundant, but very small. Silicon carbide (0.1 micron-20 micron), graphite (to 20 microns) and a few other types of minerals are the other dominant presolar grain types. Study of these grains is a very active area of current research.