Stardust. Coloured scanning electron micrograph showing a single grain of circumstellar graphite; a carbon dust particle which is found in space near a star. Grains such as this are formed from carbon in the atmospheres of dying stars, and are thrown into space as the star dies. Samples retrieved near Earth come from stars which died out before our own solar system formed, so are at least 5 billion years old. The grains typically have a concentric 'onion-like' pattern of shells, revealed best in partially-broken samples. Stardust grains are around 5 microns (millionths of a metre) in diameter.