The ice contains evidence of an ancient massive solar storm

(Inside Science) — For a few nights more than 9,000 years ago, when many of our ancestors wore animal skins, the northern sky would have been bright with twinkling lights.

Telling chemical isotopes in ancient ice cores suggest that one of the most massive solar storms ever took place around 7176 BC. J. – C., and that would have been noticed.

“We know that most high-energy events are accompanied by geomagnetic storms,” ​​said Raimund Muscheler, professor of geology at Sweden’s Lund University. “So it’s likely that there were visible auroras.”

Muscheler is the lead author of a study published in January in the journal Nature Communication reporting evidence of the ancient event that resulted in a massive flux of high-energy particles or gamma rays hitting Earth.

The event created distinctive radioactive varieties of beryllium and chlorine in the atmosphere; these isotopes then fell to the ground with the annual seasonal snowfall and were preserved in layers of ancient ice. The cause was almost certainly a solar storm of protons, electrons and ions – called solar energetic particles, or SEPs – although galactic gamma-ray bursts and supernovae have left a similar chemical signature in the ice.

Researchers have now examined ice cores from several drilling projects in Greenland and Antarctica, a difficult and time-consuming task.

In ice cores from both regions they saw evidence of three SEP events known to have occurred in AD 993 or 994, AD 774 or 775, and AD 660 and are all associated with solar storms .

But they also found evidence of another large MS event – unrecorded until now – which happened around 7176 BC, or around 9,200 years ago.

Because its strength could be estimated by the levels of the radioactive isotopes beryllium and chlorine, they determined that the solar storm of 7176 BC. AD was so violent that if a storm of similar intensity occurred today, it could have catastrophic consequences, including knocking out orbiting satellites. , disrupting communication networks and cutting power grids.

“The known events of the past 70 years, for which we have instrumental data, were all much smaller,” Muscheler said. These ancient events, he noted, were about 10 times larger.

Researchers say a puzzling feature of the 7176 BC solar storm. is that it occurred during a supposedly “quiet” phase – known as the “solar minimum” – of the 11-year solar activity cycle, when solar storms are unlikely . They warn that current risk assessments do not properly account for this possibility.

But solar physicist Dean Pesnell of NASA’s Goddard Space Flight Center, who was not involved in the study, calculates that the storm of 7176 BC did not occur during actual solar minimum, but at the beginning of a new cycle of solar activity.

Pesnell, who is the project scientist for the Solar Dynamics Observatory, said solar storms can also occur at the end of a declining phase of the solar activity cycle. “They’re not typical, but neither are they unexpected.”

Jan Janssens, a communications specialist at the Brussels Solar-Terrestrial Center of Excellence, which coordinates international solar studies, agrees with Pesnell that solar storms can occur at the very beginning or at the very end of the sun. a cycle of solar activity. “It’s possible,” he said in an email. “Obviously it doesn’t happen too often, and certainly not during a minimum solar cycle, but it does apparently happen once in a while.”

And if the solar storm did not occur during solar minimum, but instead occurred at the start of a new solar cycle, it would undermine the researchers’ warning that such storms can occur at that time and are not not properly taken into account.

The solar activity cycle is caused by the entanglement and untangling of the sun’s powerful magnetic fields. Sunspots and solar storms are more common near cycle maximums and less common near cycle minimums.

Mary Hudson, a physics and astronomy professor at Dartmouth College who studies solar storms, said that while the storm of 7176 BC. J.-C. had occurred near a solar minimum, it could have been more severe than usual. However, storms near a solar maximum could be less severe than usual, although they are more frequent. (The solar mechanism behind this apparent peculiarity is not understood, however, and some scientists dispute that it really exists.)

Hudson, who was also not involved in the ice core study, noted in an email that the famously powerful solar storm observed by astronomers in 1859, called the “Carrington Event”, happened. also produced near a solar minimum, as does the powerful solar storm. from 774 or 775 AD.

So far, the modern world hasn’t been hit very hard by solar storms. Janssens noted that they can severely damage satellites, threaten the health of astronauts in space with bursts of intense radiation, and interfere for several hours with radio signals used in communication networks and for the navigation of ships and ships. planes.

They can also damage electrical networks by creating unexpected electrical currents that overrun a network’s transformers. Some of the worst solar storms in recent memory, the “Halloween storms” of 2003, darkened parts of Europe for several hours and damaged transformers in South Africa, while an intense solar storm in 1989 darkened the Canadian province of Quebec. But Pesnell said power companies have become more risk-aware in recent years and have “hardened” their equipment against damage from solar storms.

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