Tuesday, 12 March 2019

Strongest known solar storms blasted Earth in 660 B.C.

Greenland’s ancient ice sheet holds evidence of a solar storm that struck Earth more than 2,600 years ago. Researchers found radioactive evidence of an “extreme solar event” that occurred around the year 660 BC.

It’s unclear how common such extreme events are; satellite- and ground-based instruments have tracked them for only about 70 years. To look farther back in time, researchers hunt for spikes in cosmogenic radionuclides such as carbon-14 — recorded in tree rings — or beryllium-10 and chlorine-36 — preserved in ice cores. Such radionuclides form when cosmic rays interact with molecules in Earth’s atmosphere.
The abundance of the radionuclides in the ice suggested that the 660 B.C. event was about 10 times more powerful than a 1956 event, the strongest solar storm recorded by instruments.

The only known solar storm to rival the ancient storm’s power occurred in A.D. 774–775, an event also recorded in tree rings and ice cores.