The first-ever discovery of an extraterrestrial radioactive isotope on Earth has scientists rethinking the origins of the elements on our planet. The tiny traces of plutonium-244 (Pu-244) were found in ocean crust alongside radioactive iron-60. The two isotopes are evidence of violent cosmic events in the vicinity of Earth millions of years ago.
“It must have been a supernova, not so near as to kill us but not too far to be diluted in space,” said physicist Dominik Koll, at Australian National University, about the new discovery that our planet probably picked up stray particles not naturally produced on Earth while traveling through the Local Interstellar Cloud (image above), also known as the Local Fluff, for somewhere between 40,000 and 150,000 years and will probably not emerge for another 20,000 years.
“We have the Local Bubble in the interstellar medium. We’re right on its edge,” says Adrian Melott at the University of Kansas. “It’s a giant region about 300 light years long. It’s basically very hot, very low-density gas — nearly all the gas clouds have been swept out of it. The best way to manufacture a bubble like that is a whole bunch of supernovae blows it bigger and bigger, and that seems to fit well with idea of a chain. When we do calculations, they’re based on the idea that one supernova that goes off, and its energy sweeps by Earth, and it’s over.