‘Supernova iron’ discovered on the Moon

Around 2 million years ago a dying star close to our solar system exploded in spectacular fashion, ending its life in a supernova that blasted most of the star’s material into space. As it turns out, this material landed both on the Earth and on the Moon.

That material largely comprised of new chemical elements created during the explosion.

Detection of increased concentrations of the iron isotope 60Fe in Pacific ocean deep-sea crusts and in ocean-floor sediment samples is earthly evidence of that explosion.

The radioactive 60Fe isotope has a half-life of 2.62 million years, meaning that any created at the birth of our solar system should no longer be present, instead having been already converted into stable elements. The fact that the isotope is almost exclusively created by supernovas supports the theory of the cataclysmic explosion close to Earth 2 million years ago.

Experts at the Technical University of Munich (TUM) have added weight to a theory put forward by predecessors there, who produced supernova theory 17 years ago. Along with colleagues from the US, the team have now found unusually high concentration of 60Fe in samples taken from the surface of the moon, gathered between 1969 and 1972 by several Apollo missions.

Lunar samples incredibly useful for experts

It’s possible that bombardment with cosmic particles results in 60Fe on the moon, because unlike with Earth’s atmosphere these particles do not break up when colliding with air molecules; instead they directly impact the lunar surface and can therefore result in transmutation of elements. “But this can only account for a very small portion of the 60Fe found,” explained Dr. Gunther Korschinek, physicist at TUM and scientist of the Cluster of Excellence Structure and Origin of the Universe.

Therefore, he said, “we 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.”

The moon tends to give physicists a better cosmic record compared to Earth, and the new investigation has allowed the team to judge how far away the supernova event was by measuring the upper limit of the flow of 60Fe that reached the moon.

“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.”

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Image credit: Thinkstock

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