The Northern Lights were visible much farther south than usual this year, and pictures of the colorful hues filled social media. Now, imagine an aurora hundreds of times brighter – except no one would be able to snap a photo of it, as the onslaught of particles rushing in from the sun would instantly turn smartphones into bricks.
Such extreme solar storms are rare – only six are known to have left their traces on Earth in the past 14,500 years, and none have been witnessed since the height of the Assyrian Empire nearly 2,700 years ago.
A research team led by Irina Panyushkina of the University of Arizona Laboratory for Tree-Ring Research and Timothy Jull at U of A Department of Geosciences has now pinpointed the last time there was a burst of cosmic radiation so powerful that if it happened today, it would wreak havoc on power grids, satellites and communication networks around the globe.
The team published its findings in the journal Communications Earth & Environment.
Analyzing tree-rings for carbon-14, a naturally occurring radioactive variant of carbon, the team discovered a spike dating to the year 664 B.C., pinpointing the only extreme solar storm event whose timing had long eluded researchers.
Panyushkina, lead study author and a research associate professor of dendrochronology at the Laboratory for Tree-Ring Research. said determining the precise timing of a massive solar eruption event provides important data for scientists who study and develop models of the sun's activity over time.
Carbon-14 continually forms in the atmosphere as a result of cosmic radiation, Panyushkina said. Eventually, carbon-14 reacts with oxygen to form carbon dioxide.
"After a few months, carbon-14 will have traveled from the stratosphere to the lower atmosphere, where it is taken up by trees and becomes part of the wood as they grow," Panyushkina said.
It wasn't until 2012 that extreme solar storms, known as Miyake events, were known to exist. That year, Fusa Miyake, a Japanese physicist and collaborator of Panyushkina's team, published a paper reporting the storms' telltale signature: spikes in radioactive carbon isotopes in the growth rings of trees.