High-energy protons, nuclei, and other particles are constantly showering down on Earth’s atmosphere from space, but the origins of these cosmic rays is unknown. One possibility is that the cosmic rays come from supernovae, although the evidence for this claim is limited. Now by analyzing the cosmic ray energy spectrum, scientists have been able to deduce that some high-energy cosmic rays may have originated from a two-million-year-old supernova located roughly 100 trillion miles away.
The existence of such a supernova is also intriguing because, in unrelated work, a supernova of the same age and distance has been proposed as the source of rare iron isotopes buried in the Earth’s ocean crusts. The two different sets of data – cosmic rays and iron isotopes – both seem to point to the same exploding star as their source.