It's generally accepted that several stars have gone supernova about 300 light years from Earth within the past few million years. Recent evidence for these supernovae comes from two studies published in April. In one, researchers traced the amount of iron-60, a radioactive form of iron, in deep-sea crusts. Iron-60 is catapulted into space by supernovae or in winds from massive stars; its presence can reveal when a star exploded nearby. Scientists found two influxes of iron-60, one about 1.5 to 3.2 million years ago, another at 6.5 to 8.7 million years ago. Another group calculated the likely trajectories of recent supernovae, and found that the stars were probably nine times the size of our own sun, and exploded about 300 light years from Earth.