The night sky lit up so bright that some people thought it was morning. Gold miners in the Rocky Mountains woke up at 1 a.m. to make breakfast and start their day. Birds began singing as if the sun had already risen. Telegraph systems worldwide went offline, and no one could send a message.
That event in 1859, known as the Carrington Event, has long been thought of as the benchmark for the most intense geomagnetic storm observed on Earth, sending northern lights displays as far south as Florida and Central America and knocking out communication systems. But now, new research has unveiled evidence of a much larger solar storm that could reset record books.
In a study released Monday, researchers identified what appears to be the largest solar storm to hit Earth, estimated to be larger than the Carrington Event by an order of magnitude. The storm occurred 14,300 years ago, but is evidence of a yet unknown dimension of the sun’s extreme behavior and hazards to Earth.
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“It’s clear that if one of these events [occurred] today … this would be quite destructive on our energy network and also internet network,” said Edouard Bard, lead author of the study. “This would really freeze, in fact, all communications and [travel] would be totally disrupted.”
Unlike the Carrington storm, the 14,300-year-old event does not have ground reports of bright, dancing lights or changes in animal behavior. Instead, scientists found traces of the solar storm in ancient tree rings in the French Alps and ice cores in Greenland.
The journey from space to our trees may seem fortuitous, but physics helps explain the cosmic connection, said astronomer Benjamin Pope, who was not involved in the research. Cosmic rays, or high energy particles, from space can strike Earth’s atmosphere and cause nuclear reactions. For example, the high-energy radiation can turn nitrogen atoms in our upper atmosphere into radioactive carbon-14, known as radiocarbon. The radiocarbon filters through Earth, including plants, animals, people, oceans — but also tree rings, which can preserve the records for thousands of years.
“It’s a huge interdisciplinary science involving archaeologists, chemists and physicists, which is our only real way of understanding the physics of the sun before modern times,” said Pope, a researcher at Australia’s University of Queensland.
The team measured radiocarbon levels in trees in the French Alps, which were older than previously sampled trees. Bard said typically these measurements are very boring and monotonous — but, in this case, a very distinct spike appeared in a single year 14,300 years ago.
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The amount of radiocarbon produced may have been between five to 10 times the amount normally produced in an entire year, said Tim Heaton, a co-author of the study. The team suggests the radiocarbon spike was caused by a massive solar storm or from a huge solar flare, which sent a huge amount of energetic particles into Earth’s atmosphere.
“I certainly wasn’t expecting anything as significant as this,” said Heaton, a statistician at the University of Leeds in Britain. “It looks like it might be the biggest one that’s ever been seen so far.”
The team confirmed the radiocarbon spike by analyzing ice cores in Greenland. Just as solar particles and cosmic rays can create carbon-14, they can also create beryllium-10 isotope, which can settle in ice cores. Bard said the fact that spikes were found in both data sets “is really indicating to us that the mechanism is well understood.”
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Following the spike, the study authors also found radiocarbon levels tend to stay elevated for about a century, marking a period where the sun went quiet. The sun’s activity naturally ebbs and flows through an 11-year cycle, but this event shows the peaks of several consecutive solar cycles were lower than normal — known as a grand solar minimum. Heaton explained that typically the sun’s magnetic field helps shield Earth from cosmic rays, but when the sun’s activity is lower, then more cosmic rays reach Earth enabling more radiocarbon production.
Others are not fully convinced that the data is tied to a large solar storm. Researcher Florian Adolphi, who was not involved in the study, said the researchers also need to look at the concentrations of another type of isotope, the chlorine-36 isotope, which is more sensitive to solar cosmic radiation than radiocarbon or beryllium. Bard and his colleagues are already collecting additional data, including looking at the chlorine isotope from ice cores in Antarctica.
“Similarly, it remains to be tested, whether the event was really the strongest of the so far observed events,” said Adolphi, a senior scientist at the Alfred Wegener Institute for Polar and Marine Research in Germany. Overall, Adolphi said the study was “well done,” and shows compelling evidence for another past solar event, providing a great opportunity for further research investigating the exact cause and amplitude.
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This 14,300-year-old event appears to be bigger than any on record, but is one of nine extreme solar storms to occur in the last 15,000 years, discovered in tree rings over the past decade. These extreme events are known as Miyake events, named after Japanese physicist Fusa Miyake, who first discovered the radiocarbon spikes in tree rings in 2012. No Miyake event has been directly observed, like the Carrington Event.
Pope said these Miyake events seem to occur at random, about once every thousand years. He estimated that could mean about a 1 percent risk of such an event occurring each decade, which is a threat to power grids, satellites and the internet.
“Even if these Miyake Events occur once a thousand years … I think [it] is pretty serious and definitely merits investment in understanding these events and how to predict and mitigate their effects, if any,” said Pope, who called it a really interesting study.
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Bard, a climate scientist at Collège de France and CEREGE, said learning about the sun’s past behavior is important for forecasting future solar storms, but also for understanding the sun’s impact on Earth’s climate. The sun’s effect on Earth’s climate is not as large as warming from greenhouse gas emissions, but it is a factor to consider in climate models.
“The solar activity is also changing the output of the sun,” said Bard. “We can’t assume the sun as constant. We need also to enter its behavior over long time periods in order to calculate climate variability.”
This article is part of Hidden Planet, a column that explores wondrous, unexpected and offbeat science of our planet and beyond.
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