Station, ACE operates more than 17 years. During this time she was able to detect more than 20 closely spaced to the Ground galactic sources of cosmic rays, which, in particular, in OB Association, Scorpius-Centaurus. Only in the subgroup of Upper Scorpion is 83 stars in the Upper Centaurus — Wolf — 134 lights and in the Lower Centaurus — southern cross — 97 stars.
These objects are the most likely sources of radioactive isotope Fe-60 on Earth. In contrast to the stable Fe-56, the isotope Fe-60 half-life of 2.6 million years. Preserved on Earth, these isotopes are of alien origin, and the lifetime of the isotopes restricts the distance from the Earth to their source.
According to scientists, the isotope Fe-60 are formed in the supernova explosion, which happen every few million years. The frequency of such events coincides with the observable on the Earth content of isotope Fe-60 and their decay products.
However, radioactive isotopes do not reach the Earth after the explosion of any supernova, and the increasing products of its disintegration by the shock wave from another supernova flash (scientists estimate the time delay between events is approximately one hundred thousand to several million years).
Cosmic rays are high energy elementary particles and atomic nuclei reaching the Earth. Typically, these particles are represented by protons and helium nuclei. In their origin they are divided into four groups: solar, interplanetary, galactic (which is devoted to research) and extragalactic.