The locations and timing of the closest supernovae to Earth within the last few million years are described this week in a paper published in Nature. The study models the transport of a specific iron isotope (60Fe) - produced when a supernova explodes - to Earth’s deep-sea crust, and provides insight into the formation of stars and our local stellar environment.

The presence of 60Fe in Earth’s deep-sea crusts suggests that one or more supernovae exploded in the solar neighbourhood about 2.2 million years ago, with recent analysis consistent with a distance of 60-130 parsecs, or 196-424 light years, from the Sun.

To discover the times and locations of the supernova explosions, Dieter Breitschwerdt and colleagues calculated the most probable trajectories and masses of the massive stars that became the supernovae. They report that the 60Fe signal in the Earth’s deep-sea crusts arises from two supernovae at distances of between 90 and 100 parsecs from the Sun. They find that the closest had a mass of 9.2 times that of the Sun and occurred 2.3 million years ago, and the second-closest had a mass of 8.8 times that of the Sun and occurred about 1.5 million years ago.