Just call it purple rain.
On Thursday, scientists published a study reporting findings of a material called iron-60 — a radioactive isotope found in cosmic rays — in the Earth's atmosphere. According to the Verge, the presence of the rare material suggests that multiple supernovae — star explosions — have occurred in our solar system over the last few million years.
NASA scientists have been tracking the material for the last 19 years using its Advanced Composition Explorer spacecraft, which measures solar, interplanetary, interstellar and galactic particles. Honing in on 17 years of data, the scientists found that the ACE had come in contact with 15 iron-60 nuclei.
Washington University physicist Martin Israel, the study's author, told the Verge that this discovery helps make sense of the radioactive material's presence in lunar soil and the Earth's ocean floor and crust.
Previously, scientists had been unable to account for iron-60's 2.6-million-year half-life, which meant that it couldn't have been native to Earth. Now, Israel said scientists can logically conclude the material had showered down on the planet from outer space.
"It all fits together very nicely," Israel said according to the Verge. "It's all consistent."