Supernova 'smoking gun' linked to mass extinctionsLuckily for us, the astronomers say, there is very little danger of it happening again anytime soon... The cluster, called the Scorpius-Centaurus OB association, is now positioned a safe 350 light-years from Earth. But the group says it passed within 130 light-years of Earth about two million years ago. This puts it in the right place at the right time to explain evidence uncovered on Earth by German researchers in 1999. They found atoms of a very rare isotope of iron, 60Fe, in cores taken from the ocean floor. 60Fe is rare in the solar system because it has a half-life of 1.5 million years.
by Eugenie Samuel
Star Material Discovered In South PacificInterstellar matter formed in a supernova has been discovered on Earth now for the first time. Light coming to Earth from distant supernovas is recorded all the time. Likewise, a dozen or so neutrinos from nearby Supernova 1987A have been detected. But atoms from supernovas are a different matter. In a sense, all the heavy atoms on Earth have been processed through or created in supernovas long ago and far away. But now comes evidence of atoms from a supernova that may have been deposited here only a few million years ago. An interdisciplinary team of German scientists from the Technical University of Munich (Gunther Korschinek, 011-49-89-289-14257, firstname.lastname@example.org), the Max-Planck Institute (Garching), and the University of Kiel have identified radioactive iron-60 atoms in an ocean sediment layer from a seafloor site in the South Pacific. First, several sediment layers were dated, and only then were samples scrutinized with accelerator mass spectroscopy, needed to spot the faintly-present iron. The half-life of 60Fe (only 1.5 million years), the levels detected in the sample, and the lack of terrestrial sources point to a relatively nearby and recent supernova as the origin. How recent? Several million years. How close? An estimated 90-180 light years. If the supernova had been any closer than this, it might have had an impact on Earth's climate. The researchers believe traces of the 60Fe layer (like the iridium layer that signaled the coming of a dinosaur-killing meteor 65 million years ago) should be found worldwide but have not yet been able to search for it. (K. Knie et al., Physical Review Letters, 5 July 1999.)
by Phillip F. Schewe and Ben Stein
Physics News Update
July 2, 1999