Since the moon generally provides a better cosmic record than Earth, the scientists were also able to specify for the first time an upper limit for the flow of 60Fe that must have reached the moon. Credit: © SkyLine / Fotolia
Confirmation of supernova explosion in the neighborhood of our solar system. ~2 million yrs ago a star exploded in a supernova close to our solar system: Its traces can still be found today in the form of an iron isotope found on the ocean floor. Now scientists have found increased concentrations of this supernova-iron in lunar samples as well. They believe both discoveries to originate from the same stellar explosion.
Estimation of the local fluence of Fe60 on the Moon’s surface. The dashed curves represent two different integration scenarios.
Increased concentrations of the iron isotope 60Fe detected in Pacific ocean deep-sea crusts and in ocean-floor sediment samples. This evidence is highly compelling: The radioactive 60Fe isotope is created almost exclusively in supernova explosions. And with a half-life of 2.62 million years, relatively short compared to the age of our solar system, any radioactive 60Fe originating from the time of the solar system’s birth should have long ago decayed into stable elements and thus should no longer be found on Earth.
This supernova hypothesis was first put forth in 1999 by Technical University of Munich (TUM) researchers who had found initial evidence in a deep-sea crust. Now they have succeeded in demonstrating an unusually high concentration of 60Fe in lunar ground samples as well gathered between 1969 and 1972 during Apollo lunar missions 12, 15 and 16.
The presence of iron-60 on Earth is proof that a near supernova explosion sprinkled radioactive fallout on the planet.
It’s also conceivable that 60Fe can occur on the moon as the result of bombardment with cosmic particles, since these particles do not break up when colliding with air molecules, as is the case with Earth’s atmosphere. Instead they directly impact the lunar surface and can thus result in transmutation of elements. “But this can only account for a very small portion of the 60Fe found,” explains Dr. Gunther Korschinek. “We therefore assume that the 60Fe found in both terrestrial and lunar samples has the same source: These deposits are newly created stellar matter, produced in one or more supernovae,” says Dr. Korschinek.
Since the moon generally provides a better cosmic record than Earth, the scientists were also able to specify for the first time an upper limit for the flow of 60Fe that must have reached the moon. Among other things this also makes it possible for the researchers to infer the distance to the supernova event: “The measured 60Fe-flow corresponds to a supernova at a distance of about 300 light years,” says Korschinek. “This value is in good agreement with a recently theoretical estimation published in nature.” The lunar samples were investigated using the high-sensitivity accelerator mass spectrometer of the Maier-Leibnitz Laboratory near Munich. http://www.eurekalert.org/pub_releases/2016-04/tuom-sif041416.php
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