Stardust in Our Hands

Abstract

Although every atom in our body has at one time been inside a star or was made by a star, atoms are elementary constituents of our body. They have been recycled many times through various chemical reactions, and absorbed by our bodies through eating and breathing. It seems rather unlikely that we can pick up a piece of material that was made by a star and is preserved in its original form. It was therefore a total shock when, in 1987, Ernst Zinner and his group at Washington University in St. Louis, Missouri, was able to identify certain diamond and silicon carbide particles in primitive meteorites were to be of pre-solar origin based on their isotopic composition. Isotopes are the same chemical elements but with a different number of neutrons in their nuclei. For example, the element oxygen can have 8, 9, or 10 neutrons in addition to 8 protons in the nuclei. Usually, the ratios among different isotopes of the same elements are determined by their nucleosynthesis history, and objects in the Solar System all have pretty much the same isotopic ratios. Stellar materials, however, have different isotopic ratios than the Solar System value and therefore can be distinguished. These small solid grains can be traced directly to carbon stars or supernovae, giving the first direct evidence that stardust can be transported intact across the Galaxy to the Solar System.