Research Highlights

Huge solar storm kept on ice

Published online 13 March 2019

A study of ancient ice cores and tree rings reveals that a powerful burst of high-energy protons from the Sun hit Earth about 2,700 years ago.

Tim Reid

A corona mass ejection (CME), associated with a solar flare, photographed by NASA's Solar Dynamics Observatory spacecraft on 1 May 2013. CMEs carry over a billion tons of particles at over a million miles per hour.
Courtesy of NASA/SDO and the AIA, EVE, and HMI science teams

Explosive events in the Sun such as solar flares or coronal mass ejections sometimes send bursts of highly energetic particles towards Earth, posing a threat to satellites, communications systems and aircraft. While modern detectors have measured various small solar bursts since the 1950s, larger events from the past must be inferred by examining natural records, such as ice cores and tree rings. Specifically, these records show increased levels of radionuclides that are produced by the impacts of solar particles.

Raimund Muscheler at Lund University, Sweden, Ala Aldahan at United Arab Emirates University, and co-workers in Switzerland, France, Korea and the USA were intrigued by a peak in levels of the carbon-14 radionuclide in German oak tree rings from around 660 B.C. To investigate further, the team analysed data for the same period from two Greenland ice cores, finding similar strong peaks in beryllium-10 and chlorine-36.

Using knowledge about the conditions required to produce these radionuclides, the researchers estimated the energy distribution that the solar protons must have had. These energies and the number of protons were too high to be explained as part of the regular 11-year solar cycle, and were similar to the largest known solar event to date, which occurred around A.D. 775.

“Our research indicates that the Sun can produce much larger solar storms than expected,” says Muscheler. “These events are probably rare, but they could have huge impacts on our society, and must be included in future risk analyses regarding the possible effects of solar storms.”

doi:10.1038/nmiddleeast.2019.36

O’Hare, P. et al. Multiradionuclide evidence for an extreme solar proton event around 2,610 B.P. (∼660 BC). PNAS http://dx.doi.org/10.1073/pnas.1815725116 (2019).