-
Plutonium discovered at the bottom of the ocean was found to be refuse from a kilonova that exploded close to Earth 10 million years ago.
-
Kilonovas occur when binary neutron stars spiral closer and closer to each other until they finally collide and release tons of heavy elements into space.
-
Our best chance of finding more evidence of this kilonova is on the lunar surface, which is not affected by the same weather phenomena as Earth.
Headed for your next beach getaway? You’re probably going to be floating around in the debris of ancient star explosions.
When supermassive stars gasp their last proverbial breath and go supernova, they release tons of heavier elements into space, and some of that refuse has drifted down to Earth. Astronomer Brian Fields of the University of Illinois Urbana-Champaign has now found evidence of something even more explosive. He and his research team discovered traces of a radioactive plutonium isotope from the deep sea that are actually remnants of a kilonova—the collision of two neutron stars—that is thought to have happened relatively close to Earth about 10 million years ago.
Fields, who declared that we live in a “supernova graveyard” during a recent presentation at the 2025 American Physical Society Global Physics Summit, has been analyzing cosmic debris from both Earth and the Moon for decades. He had previously found the refuse from supernovae that went off 3 million years ago and 8 million years ago. Later, he discovered plutonium in those samples, meaning it would have been impossible for the debris samples to have come from either of those supernovas.
Stars whose lives end in a supernova have exhausted all their hydrogen and fused it into helium. When they run out of helium, they keep fusing that into heavier elements until they get to iron, which they can no longer fuse because it is too stable. These stars are so massive (at least 8 solar masses) that gravity causes them to collapse in on themselves. Those with the most enormous cores become black holes. When the cores of slightly smaller stars collapse, they end up fusing most of their electrons and protons into neutrons, morphing into unbelievably hot and dense neutron stars.
If neutron stars are orbiting each other in a binary system, gravitational forces keep them spiraling closer and closer together until they crash spectacularly. Elements heavier than iron emerge from what is known as the rapid neutron-capture process or r-process. The force of the collision blasts existing isotopes with neutrons at such incredible speeds that they can form many elements heavier than iron, and a blaze of light comes from those elements that radioactively decay into lighter ones. Earth has been showered with gold, platinum, thorium and other heavy elements.
That’s how plutonium can wind up at the bottom of the ocean. The only problem is that geological processes on Earth, such as plate tectonics and all sorts of weather phenomena, have scattered supernova and kilonova dust everywhere. However, any explosion close enough to Earth to leave behind stardust must have also left some on the Moon, which may get hit by meteoroids and solar wind particles but does not experience weather like Earth does. Anything that falls on the lunar surface tends to stay where it landed.
On the Moon, the remains of dead stars which exploded millions or even billions of years ago probably haven’t gone anywhere. They could reveal more about the kilonova that rocked nearby space in the distant past. This is why Fields insists that collecting samples with this material should be an objective for the Artemis III mission, which will be the first to put boots on the moon since the Apollo era.
By the way, about that plutonium, you don’t need to worry because it’s so far down chances are you won’t be wading or swimming or surfing anywhere near it.
You Might Also Like