Supernova Debris On Earth

Supernova debris on earth,in the form of deposits of iron-60, a radioactive isotope of iron occurring on our planet at much smaller levels, has been studied by German physicists. The same team of scientists reported first signs of the deposits five years ago (Update 437). Back then they analyzed three layers of South Pacific sediment, each over 2 million years thick in geologic time.

The new measurements, acquired at a site some 3000 km away, are much more robust: 28 layers (rather than 3), from deeper depths (4830 m rather than 1300 m), with a better dating method (beryllium-10 dating) and a more accurate estimate of the layers' age (in some cases to within a few 100,000 years). On the basis of their measurement, the researchers deduce that the samples represent the remains of a star that exploded 2.8 million years ago (with an uncertainty of 0.3 million years) at a distance from Earth of some tens of parsecs.

What, if any, were the implications of this splash of foreign matter at the time? Gunther Korschinek at the Technische Universitat Muenchen (gunther.korschinek@ph.tum.de) says that depending on exactly how far away the supernova was, it might have had caused an increase in cosmic ray flux for about 300,000 years. (Knie et al., Physical Review Letters, 22 October 2004; accelerator-analysis website at http://www.bl.physik.uni-muenchen.de/gams/index.html)