Ice preserves evidence of an ancient, massive solar storm
Analysis of radioactive chemicals in ice cores shows that Earth was once hit by the strongest solar storm ever recorded.
Telltale chemical isotopes found in ancient ice cores suggest that one of the most massive solar storms ever occurred around 7176 BCE.
“We know that most high-energy events are accompanied by geomagnetic storms,” said Raimund Muscheler, a geology professor at Lund University in Sweden.
In a study published in Nature Communications in January, researchers presented evidence of the ancient event, which caused a massive influx of high-energy particles or gamma radiation to hit the Earth.
The event created distinct radioactive types of beryllium and chlorine in the atmosphere. These isotopes fell to the ground with seasonal snowfall and were preserved in ancient ice layers. The cause was almost certainly a solar storm made up of protons, electrons, and ions — known as solar energetic particles (SEPs) — though galactic gamma bursts or supernovae would leave similar chemical signatures in the ice.
Researchers analyzed ice cores from multiple drilling projects in Greenland and Antarctica — a challenging and time-consuming task.
In ice cores from both regions, they identified three known SEP events that occurred in CE 993 or 994, CE 774 or 775, and 660 BCE, all linked to solar storms.
But they also found evidence of another large — previously unrecorded — SEP event, which occurred around 7176 BCE, about 9,200 years ago.
By estimating its strength through the levels of radioactive beryllium and chlorine isotopes, they determined the 7176 BCE solar storm was so intense that if a similar storm were to occur today, it could have catastrophic consequences — including satellite failures, disruption of communication networks, and power grid blackouts.
“The known events of the past 70 years, for which we have instrumental data, were all much smaller,” said Muscheler, noting that these ancient events were roughly 10 times stronger.
One mysterious feature of the 7176 BCE storm is that it appears to have occurred during the supposed “quiet” phase of the Sun’s 11-year activity cycle — the so-called solar minimum, when solar storms are considered unlikely. The researchers warned that current risk assessments may not properly account for this possibility.
However, Dean Pesnell, a solar physicist at NASA’s Goddard Space Flight Center who was not involved in the study, calculates that the 7176 BCE storm did not occur during the actual solar minimum but rather at the start of a new solar cycle.
Pesnell, a scientist with the Solar Dynamics Observatory project, said solar storms can also occur at the end of the declining phase of a solar cycle. “They’re not typical, but they’re also not unexpected.”
Jan Janssens, a communications specialist at the Solar-Terrestrial Centre of Excellence in Brussels, which coordinates international solar research, agreed with Pesnell that solar storms can occur at the very beginning or end of a solar activity cycle. “It’s possible,” he said in an email. “Clearly, it doesn’t happen very often — and certainly not during the solar minimum — but it does appear to happen occasionally.”
If the solar storm occurred at the start of a new solar cycle rather than during a minimum, it would undermine the researchers’ warning that such storms can occur during quiet periods and go unaccounted for.
The solar activity cycle is caused by the twisting and untwisting of the Sun’s strong magnetic fields. Sunspots and solar storms are more common near cycle peaks and less common near the minimum.
So far, the modern world has largely been spared from major solar storms. Janssens noted that they can severely damage satellites, pose radiation risks to astronauts in space, and disrupt communication networks and radio signals used for navigation on ships and aircraft for hours.
They can also damage power grids by generating unexpected electric currents that overload transformers.
The worst recent solar storms — the 2003 “Halloween storms” — caused blackouts in parts of Europe for several hours and damaged transformers in South Africa. A severe solar storm in 1989 blacked out Quebec province in Canada.
Pesnell noted that power providers have become more aware of such risks in recent years and have “hardened” their equipment against solar storm damage.
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