Ocean rocks reveal evidence that a star explosion hit Earth 10 million years ago

Star explosions don’t just happen in movies, they’re real and frequent cosmic events. New evidence seems to show that one such supernova smashed our corner of space about 10 million years ago, hitting Earth with high doses of cosmic rays.

Clues sit in metal rich rocks on the Pacific seafloor, and they tell a story written by particles from space.

Lead author Efrem Maconi from the University of Vienna, and colleagues asked a simple question with big stakes:

“Did a nearby supernova send a surge of cosmic rays toward Earth just when those rocks recorded a spike in a rare isotope?”

Earlier this year, deep Pacific ferromanganese crust samples showed a sharp rise in beryllium-10 around 10.1 million years ago.

This isotope is a cosmogenic nuclide, created when high energy particles hit atoms in the upper air.

Understanding supernovae – the basics

A supernova is the explosive death of a star. These massive cosmic events release a flood of light, high-energy particles, and radiation.

Astronomers group them into two main types: massive stars that run out of fuel and collapse (core-collapse supernovae), and white dwarfs that ignite runaway fusion in binary systems (Type Ia).

These blasts briefly outshine entire galaxies and forge many of the heavy elements in your body and in Earth’s crust.

Space is huge, though, and distance matters. The energy spreads out as it travels, so most supernovae are too far away to affect us beyond putting on a great show for telescopes.

If a supernova went off within roughly 30 light-years, it could strip part of Earth’s ozone layer, letting in extra ultraviolet light and stressing ecosystems.

Even at a few hundred light-years, a strong event might nudge ozone chemistry and raise cosmic ray levels for a while, but not enough to wipe out life.

Ocean rocks and star explosions

The team that measured the crusts saw a signal that stood out cleanly from the background. They dated the anomaly to between 11.5 and 9.0 million years ago, with a single peak at 10.1 million years.

“At around 10 million years, we found almost twice as much beryllium-10 as we had anticipated,” reported Dr. Dominik Koll from the Helmholtz Zentrum Dresden Rossendorf (HZDR).

Maconi’s group looked for likely sources in the stellar neighborhood.

They traced the motions of open cluster groups relative to the Sun and asked which ones could have hosted a star that died at the right time.

Their new letter used Gaia astrometry to rewind the orbits of 2,725 clusters over the last 20 million years.

The analysis found a 68 percent chance that at least one star exploded within about 326 light-years during the beryllium spike.

Origin of the star explosion

Two clusters rise to the top as candidates. Open star cluster ASCC 20 gets closest, roughly 110 light-years at minimum around 11.8 million years ago.

Another, OCSN 61, stays farther, not closer than about 196 light-years, but it could have contributed if the event happened at that range. The probability spread increases with distance out to about 326 light years.

None of the clusters come within roughly 65 light-years.

Recent modeling indicates that the most serious biosphere effects from cosmic ray driven supernova scenarios are unlikely beyond about 65 light-years, and that lethal cases center nearer to 65 to 20 light years.

Sun’s past location

Ten million years ago, our system sat in a busier part of the local Milky Way.

The path crossed a long, wavy chain of gas and young stars called the Radcliffe Wave, which maps the spine of nearby star formation.

This structure was charted with three dimensional dust maps and Gaia, and it reshaped how we see our backyard.

The discovery paper identified a 9,000 light year long gas ribbon that threads many well known clouds.

Other possible causes

Geology is a fair rival to astrophysics here. Changes in Antarctic ocean circulation about 10 to 12 million years ago could concentrate beryllium-10 in the Pacific without changing production in the air.

The Sun’s heliosphere, the magnetic bubble that shields cosmic rays, could also have shrunk if the solar system entered a dense cloud. That would let more cosmic rays in without any nearby star blowing up.

“Only new measurements can indicate whether the beryllium anomaly was caused by changes in ocean currents or has astrophysical reasons,” said Dr. Koll.

Researchers have already found traces of live iron 60 in Earth materials. That isotope forms in massive stars and their explosions, and it rides to us on dust.

A global survey reported two distinct influxes in the last 10 million years along with tiny amounts of plutonium 244. Those signals point to one or more nearby events that sprinkled interstellar debris across our planet.

Iron rich dust moves far slower than near light speed cosmic rays. A time offset is possible, where 10Be from particle cascades peaks first, and dust carried isotopes arrive later.

Star explosions and Earth safety

The new probability map starts near zero inside about 114 light-years and grows with distance. It rises steadily to the 68 percent figure by about 326 light-years.

Open star cluster ASCC 20 dominates the closer bin, and OCSN 61 dominates beyond roughly 228 light-years.

The modeling does not place any candidate within the hazard range that is most worrisome for the ultimate survival of life on Earth.

Independent records from outside the Pacific are essential. If the anomaly appears worldwide, an astrophysical cause of these readings starts to become more likely.

If it remains regional, ocean circulation or sediment processes become the better bet. Either way, the signal could serve as a new time marker for rocks that formed in that window.

The Sun’s past route matters too. The Radcliffe Wave context suggests our system shared space with many young clusters that could have birthed massive stars in that era.

Better constraints on cluster ages, masses, and membership will sharpen the odds. Better transport models for cosmic rays and dust will help match timing across isotopes.

The study is published in Astronomy & Astrophysics.

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