When a dying star reaches the last stage of its life, it goes out with a bang. Most stars end with a cataclysmic explosion and turn into supernovae. Now, though, scientists have discovered that supernova iron can be found on the moon.
What's interesting is that supernovae likely occurred close to Earth in the ancient past. How do we know this? It's all down to the iron isotope 60Fe. This particular isotope is created almost exclusively in supernovae explosions. While it's almost only created at the end of a star's life, though, it can be found in Pacific Ocean deep-sea crusts. This hints that in Earth's past, material from such an explosion hit our planet.
The idea that an ancient supernova impacted Earth has been around since 1999. That's when researchers found initial evidence in deep-sea crust. Now, however, scientists may have more proof that this occurred. They've found an unusually high concentration of 60Fe in samples from our moon.
The samples themselves were first gathered between 1969 and 1972 during the Apollo lunar missions. The material was then brought back to Earth. It's possible that the samples could have been contaminated, but it's very unlikely.
It's also possible that 60Fe can occur on the moon as the result of bombardment due to cosmic particles. These particles don't break up when colliding with air molecules, which is the case with Earth's atmosphere. Instead, they impact the lunar surface and can result in transmutation of elements. With that said, this can only account for a very small proportion of the material.
"But this can only account for a very small portion of the 60Fe found," said Gunther Korschinek, physicist at TUM and one of the researchers involved in the new study. "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."
The results show that a supernova event occurred in the ancient past. It's likely that this supernova happened at a distance of about 300 light-years and blasted material toward the moon and Earth.
The findings were published in the April 13 issue of the journal Physical Review Letters.
