Presolar Grains in Meteorites
Presolar grains are tiny dust particles that are literally bits of stars we can study in the laboratory. They condensed from the gas phase in the cooling outflows of stars (such as red giants and supernova explosions) billions of years ago, before the formation of our solar system. These dust grains became swept up in the interstellar medium and eventually made their way into the cloud of gas and dust ("molecular cloud") from which the Sun, Earth and planets formed 4.6 billion years ago. Most of the pre-existing dust in the Sun's parent molecular cloud (at least the dust that was in what became the inner solar system where the Earth now sits) was vaporized as the forming solar system heated up. However, a small fraction of the dust survived solar system formation, protected inside asteroids. Occasionally, pieces of these asteroids fall to the Earth and are called "primitive meteorites." By breaking up the meteorites and dissolving them away in strong acids, we have been able to isolate some of the presolar stardust. The entire process is illustrated by the cartoon below:
Because the atoms in the grains are the original atoms from the parent stars, by studying this dust we can probe processes that occur inside stars and in the interstellar medium. Thus, the discovery of presolar grains has essentially opened up a new branch of astronomy, where laboratory microanalytical instrumentation takes the place of telescopes.
© Larry R. Nittler Last modified May 20, 1999