Both meteorites were found in Antarctica, and appear to date from before the solar system was born 4.6 billion years ago. Each contains a single grain of silica (SiO2, which is the main ingredient of sand). The chemical signature of these grains is identical, and extremely rare — so rare, in fact, that scientists suspect both grains came from a single supernova. This type of supernova occurs when a massive star runs out of fuel for nuclear fusion and collapses in on itself in a giant explosion.