Solar blasts that could have badly damaged electrical grids and disabled satellites in space narrowly missed Earth in 2012.
The bursts matched the severity of the 1859 Carrington event, the largest solar magnetic storm ever reported on the planet, and would have wreaked havoc on the Earth's magnetic field, according to University of California, Berkeley research physicist Janet Luhmann.
The historical blast knocked out the telegraph system across the US and the Northern Lights lit up the night sky as far south as Hawaii, but a 2013 study by Lloyds insurance market estimated that a solar storm like the Carrington Event could cost the US economy up to $2.6tn (£1.6bn).
"Had it hit Earth, it probably would have been like the big one in 1859, but the effect today, with our modern technologies, would have been tremendous," Luhmann said in a statement.
The event, detected by NASA's STEREO A spacecraft, is the focus of a paper that was released in the journal Nature Communications on Tuesday by Luhmann, China's State Key Laboratory of Space Weather professor Ying Liu and their colleagues.
Massive bursts of solar wind and magnetic fields, shot into space on July 23, 2012, would have been aimed directly at Earth if they had happened nine days earlier, Luhmann said.
A considerably smaller event on March 13, 1989, led to the collapse of Canada’s Hydro-Quebec power grid and a resulting loss of electricity to six million people for up to nine hours.
“An extreme space weather storm — a solar superstorm — is a low-probability, high-consequence event that poses severe threats to critical infrastructures of the modern society,” said Liu, who is also a member of the National Space Science Centre of the Chinese Academy of Sciences in Beijing.
“The cost of an extreme space weather event, if it hits Earth, could reach trillions of dollars with a potential recovery time of 4 to 10 years. Therefore, it is paramount to the security and economic interest of the modern society to understand solar superstorms.”
The bursts from the sun, called coronal mass ejections, carried southward magnetic fields and would have clashed with Earth's northward field, causing a shift in electrical currents that could have caused electrical transformers to burst into flames, Luhmann said. The fields also would have interfered with global positioning system satellites.
Although coronal mass ejections can happen several times a day during the sun's most active 11-year cycle, the blasts are usually small or weak compared to the 2012 and 1859 events, she said. This event was also particularly unusual because it happened during a very calm solar period.
“Observations of solar superstorms have been extremely lacking and limited, and our current understanding of solar superstorms is very poor,” Liu said. “Questions fundamental to solar physics and space weather, such as how extreme events form and evolve and how severe it can be at the Earth, are not addressed because of the extreme lack of observations.”
Luhmann said that by studying images captured by the sun-observing spacecraft, scientists can better understand coronal mass ejections and predict solar magnetic storms in the future.
"We have the opportunity to really look closely at one of these events in all of its glory and look at why in this instance was so extreme," Luhmann said.