New findings have revealed that a supernova struck Earth 10 million years ago, and the evidence lies at the bottom of the sea. An unexpected deep-sea deposit could be irrefutable proof of a nearby star that exploded as a supernova in the relatively recent past. Specifically, a recent article in Astronomy & Astrophysics explores the possibility that this marine discovery points to a supernova that occurred 10 million years ago, when Earth was going through the Late Miocene.
This radioactive isotope is formed when cosmic rays strike Earth’s atmosphere
What scientists found were sediments at the bottom of the Pacific Ocean containing large quantities of beryllium-10. This radioactive isotope is formed when cosmic rays strike Earth’s atmosphere. From there, it falls, sinks, and is deposited on the seabed before becoming embedded in the crust. The presence of the isotope itself wasn’t unusual, but its accumulation in such high concentrations about 10 million years ago was. An anomalous event caused this spike in beryllium-10. One plausible explanation is that a supernova exploded near Earth around that time.
To understand the context, given that the beryllium-10 rain is fairly constant across the planet, the rock record should be similarly uniform. However, the team found a strange concentration dating back about 10 million years. Numerous studies indicate that during its nearly 4.6 billion years of existence, Earth has walked through graveyards of dead stars and preserved the traces of those encounters on its surface. The researchers used data from the European Space Agency’s Gaia survey to track the trajectories of the Sun and 2,725 nearby star clusters over the past 20 million years and calculate how many supernovae should occur, on average, in those clusters during that time. The field presents significant challenges, as it involves, among other things, reconstructing the path of the solar system around the Milky Way as well as the trajectory of any particles ejected by a hypothetical supernova.
The team also identified 19 clusters with more than a 1% probability of a supernova occurring
Experts discovered that there was approximately a 68% chance of a star exploding within 326 light-years of the Sun within one million years of the beryllium-10 peak. The researchers also noted that, of the 2,700 star clusters mapped, at least 19 had a greater than 1% probability of having produced a supernova near the Sun. The team also identified 19 clusters with more than a 1% probability of a supernova occurring at that distance, around the time of the anomaly.
“Our results support the possibility of a supernova origin for the beryllium-10 anomaly”
One of the key points is that the beryllium-10 anomaly appears only in one ocean. To solidify the theory, isotopes of the same age would need to be found elsewhere on the planet. Furthermore, other classic traces of cosmic explosions, such as iron-60, are missing from that same time period. “Our results support the possibility of a supernova origin for the beryllium-10 anomaly,” the team writes in their paper. Although the data strengthen the hypothesis that Earth received supernova particles during that time, the authors urge caution. The fact is that if the spike is localized only in certain parts of the Pacific Ocean, this suggests that some local force, such as a change in ocean currents, concentrated the beryllium-10 there.
“In conclusion, we find that a nearby supernova remains a possible explanation for the beryllium-10 anomaly, especially given the solar system’s proximity to the Orion region during that period. The estimated supernova probability is non-zero at 35 parsecs and increases with distance, with ASCC 20 and OCSN 61 emerging as the most promising candidate groups,” the authors said. However, if a cosmic cause exists, the same peak should be present worldwide at the same age, so taking and analyzing samples from different locations could help unravel the mystery.