In the last decade, scientists have discovered traces on Earth of six intense bursts of radiation, known as Miyake events, scattered over the last 9,300 years. The most popular explanation is that these mysterious signatures were left behind by massive solar storms, leading some scientists to warn that the next Miyake event could cripple the world’s electrical grid. But new research, published in the October Proceedings of the Royal Society A, suggests that might be behind the enigmatic radiation.
Science News headlines, in your inboxHeadlines and summaries of the latest Science News articles, delivered to your email inbox every Thursday.
Miyake events were first discovered in trees. As trees grow, their trunks accrue layers, or rings, which lock in chemical signatures from their surroundings. By analyzing the composition of individual tree rings, researchers can uncover clues about environmental conditions going back thousands of years (SN: 6/1/20).In 2012, physicist Fusa Miyake of Nagoya University in Japan was studying Japanese cedar tree rings when she found — a variant of carbon that can form when cosmic radiation strikes Earth’s atmosphere — in rings dating to about A.D. 774. Since then, , now named Miyake events, have been detected in tree rings around the world as well as in .
Due to the spikes’ global occurrence, many scientists contend that the events have an extraterrestrial origin. The most popular explanation is that especially large solar storms, or flares, blasted Earth with big bursts of radiation (SN: 2/26/21).The most powerful solar storm in recorded history was the , which broke telegraph lines and sparked a circuit fire in Pittsburgh. The radiation levels associated with Miyake events are more than 80 times those of the Carrington event, says physicist Benjamin Pope of the University of Queensland in St. Lucia, Australia. “They could pose serious risks to global technology.” But the solar storm story has holes. Radiation levels from the 774 event to have come from a single solar flare, some researchers have suggested. And ice cores, which can also store chemical traces of solar flares, have not yet yielded evidence of increased solar activity . So, Pope and his colleagues put the leading hypothesis to the test. They analyzed all publicly available tree ring data on the six Miyake events using computer simulations of Earth’s carbon cycle. This allowed the team to calculate the duration, timing and amplitude of each event.