Exploding stars scattered traces of iron over Antarctic snow

Unlike previous similar detections, the interstellar material dribbled down on Earth recently

by EMILY CONOVER

supernova Vela
SUPERNOVA SNOWFALL Scientists have found a fingerprint of exploding stars, or supernovas, in Antarctic snow that fell within the last 20 years. Here, part of a supernova remnant, Vela, is shown.

Iron from outside the solar system has sprinkled down on Antarctica in recent years. Measurements of half a ton of snow turned up interstellar iron deposited within the last two decades, scientists report in a study accepted in Physical Review Letters. That iron comes from the explosions of massive stars, or supernovas, the team says.

Within the snow, the researchers isolated 10 atoms of iron-60, a radioactive variety, or isotope, of iron with a total of 60 protons and neutrons in its nucleus. Previous studies have found iron-60, an isotope spewed from supernovas, in ocean sediments and on the moon (SN: 7/10/99, p. 21). But those depositions were a few million years old, and are thought to be the result of ancient nearby explosions blasting waves of debris through space. The new study reveals that the Earth is still encountering the isotope in modern times.

Nuclear physicist Gunther Korschinek of the Technical University of Munich and colleagues transported the snow — still frozen thanks to careful packing and shipping — back to their lab. They melted, filtered and evaporated the snow, and used a technique called accelerator mass spectrometry on the remnants to identify iron-60.

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