When several of the Apollo missions returned from the moon between 1969 and 1972, they brought back samples of the lunar soil. New research into some of those samples has revealed that those missions also brought back something else – the remnants of a star that died near our solar system about two million years ago.

When researchers at the Technical University of Munich (TUM) analyzed the soil brought back by Apollo missions 12, 15 and 16, they found high levels of an iron isotope known as 60Fe. This element is created almost exclusively when a star dies and goes supernova in a massive explosion that spews gas and other material into the universe.

While it's possible that the lunar soil got some 60Fe through bombardment from cosmic particles, Dr. Gunther Korschinek, physicist at TUM, says that the amount they discovered was well in excess of simple background particle accumulation on the moon's surface. Also, because 60Fe has a half life of 2.62 million years, the researchers are able to conclude that it got deposited on our moon no more than that long ago – a relatively short time in terms of our galaxy, which is estimated to be over 13 billion years old.

This isn't the first time scientists have discovered 60Fe in our neighborhood. It was previously found in deep-sea crusts and ocean-floor sediment beneath the Pacific Ocean, where it's believed it accumulated from the same supernova explosion.

Because elements that reach the moon's surface don't degrade as they collide with air molecules as they do on Earth, the researchers were also able to use the lunar 60Fe to determine that the supernova from which the radioactive iron came was only about 300 light years from our own planet.

Korschinek told Gizmag that the lunar soil he and his team worked with was obtained from NASA's CAPTEM, the Curation and Analysis Planning Team for Extraterrestrial Materials.

While the discovery was first detailed in a 2004 dissertation from TUM physicist Leticia Fimiani, the findings were just published in the journal Physical Review Letters on April 13.