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2019-08-19. A Supernova Was Hiding in Antarctica’s Snow.

posted Aug 21, 2019, 8:15 PM by Alan Gould
By Katherine Kornei, The New York Times. [https://www.nytimes.com/2019/08/19/science/antarctica-snow-supernova.html] For GSS A Changing Cosmos chapter 6. Excerpt: Earth is continuously plowing through extraterrestrial dust. Tens of thousands of tons of the stuff, mostly from asteroids and comets, settles all over the planet every year. ...Recently, scientists analyzed dust collected from Antarctic snow and found an excess of radioactive iron. After ruling out contamination from nuclear weapons testing and other sources, the team concluded that the iron was produced by supernovas, fleeting explosions of stars more massive than the sun. This discovery suggests that stellar blasts might have rocked Earth and the rest of the solar system in the not-too-distant past. The results were published on Aug. 12 in Physical Review Letters [https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.123.072701]. Meteorite hunters are drawn to Antarctica because the space rocks, which are dark, stand out against the snow. Dominik Koll, a doctoral candidate in nuclear physics at the Australian National University in Canberra, appreciates Antarctica for other reasons: its remote location and desert climate, which ensure that whatever extraterrestrial dust falls from the sky remains relatively uncontaminated and undiluted. In 2015, a colleague of Mr. Koll’s collected roughly 1,100 pounds of snow near Kohnen Station in Antarctica. ...The researchers were looking for a rare, unstable variety of iron containing 26 protons and 34 neutrons. This radioactive isotope, iron-60, is produced by supernovas. ...Iron-60 has been found on Earth in oceanic crust that is millions of years old and on the surface of the moon, indications that the isotope circulated through the solar system long ago. But iron-60 from supernovas has never been found in geologically young material; its discovery in relatively fresh snow would suggest that it’s still raining down on Earth....