Samples from moon confirm supernova explosion created radioactive iron

Scientists used samples from Moon to confirm a supernova explosion that happened in the neighbourhood of our solar system about two million years ago. A star exploded in a supernova close to our solar system and its traces can still be found today in the form of an iron isotope found on the ocean floor. Now scientists at the Technical University of Munich (TUM), and colleagues from the US, have found increased concentrations of this supernova-iron in lunar samples as well. They believe both discoveries to originate from the same stellar explosion.

A dying star ends its life in a cataclysmic explosion, shooting the majority of the star’s material, primarily new chemical elements created during the explosion, out into space. One or more such supernovae appear to have occurred close to our solar system approximately two million years ago.

Evidence of the fact has been found on the Earth in the form of 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.

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 the Earth.

This supernova hypothesis was first put forth in 1999 by researchers at the Technical University of Munich (TUM) who had found initial evidence in a deep-sea crust. Now, researchers have succeeded in demonstrating an unusually high concentration of 60Fe in lunar ground samples as well.

The samples were gathered between 1969 and 1972 during Apollo lunar missions 12, 15 and 16, which brought the lunar material back to Earth. It is 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 the 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,” said Gunther Korschinek, physicist at TUM. “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,” said Korschinek.