Recent detections of iron-60 in ocean sediments reveal that Earth has been passing through a vast cloud of gas and dust from a supernova explosion for approximately 33,000 years.
As Earth orbits the Sun, our Solar System drifts through the Milky Way, completing one rotation every 225 to 250 million years—much like the hundreds of billions of other stars in our galaxy.
Supernovae explode roughly every 50 years somewhere in the Milky Way. Given the galaxy's vast diameter of about 150,000 light-years, such events occur once every few million years within 400 light-years of the Sun.
Over Earth's 4.5-billion-year history, our planet has encountered supernova remnants multiple times, statistically speaking.
These explosions have sculpted the interstellar medium our Solar System traverses. Though the "interstellar void" seems empty, it's filled with extremely diffuse gas and dust.
Astronomers measure variations in this medium's density by comparing stars of similar luminosity. Dimmer stars indicate dust extinction, where gas and dust absorb light.
Observations of nearby stars map a denser cloud—0.3 atoms per cubic centimeter versus the local interstellar medium's 0.05—spanning roughly 30 by 40 light-years. Remarkably, we're inside it, known as the Local Bubble.
Millions of years ago, ancient ocean bacteria incorporated iron particles, including radioactive iron-60 from supernovae, to align with Earth's magnetic field.
Fossilized remains show iron-60 use around 6 million years ago and 1.7 to 3.3 million years ago, confirming past supernova dustfalls on Earth.
Today, researchers at the Australian National University detected iron-60 atoms in marine sediments deposited over the past 33,000 years. A 2023 study also found it in Antarctic snow, suggesting arrivals within the last 20 years.
This evidence indicates Earth has been traversing supernova "ashes" for at least 33,000 years.
The debris likely originates from the Scorpius-Centaurus Association (Sco-Cen), 400 light-years away, home to massive O- and B-type stars that explode as supernovae after short lives.
ESA data from 1997 shows our Solar System was nearer Sco-Cen 5 to 7 million years ago, supporting repeated passages through its supernova remnants.
