If Earth were struck by a superflare – extremely strong explosions on the surface of stars, with energies ten thousand times higher than solar flares – life on the planet could be wiped out.

Scientists say it is least likely to happen now, but evidence suggests that it may have already occurred thousands of years ago.

Superflares That May Have Hit Earth

Christoffer Karoff, a researcher from Aarhus University, Denmark, said small superflares may have already hit Earth thousands of years ago. Evidence from tree rings indicate that the sun may have produced a small superflare in AD 775, and another in AD 993.

Strangely large quantities of the radioactive isotope 14C were discovered to have formed in Earth's atmosphere. This isotope is formed when cosmic ray particles enter our planet's atmosphere, originating from the Milky Way or from energetic solar protons that formed in connection with solar eruptions.

Data from China's Guo Shou Jing telescope, which Karoff and his colleagues used for their study, supports the theory that the event in AD 775 may have been a small superflare.

With that, our sun should experience a small superflare every millennium or 1,000 years, the study said.

Examining The Past

The strongest recorded solar storm our planet has encountered is known as the "Carrington event," in which dark spots on the sun's surface lit up and shone brightly. The particles from this solar eruption had reached Earth, causing telegraph systems across the world to go haywire.

Four years ago, superflares were first detected by astronomers. Back then, experts had yet to understand the mechanism behind the powerful event.

Now, they believe superflares would theoretically be thousands-fold stronger than solar flares. Even more resonant than the Carrington event.

Karoff said superflares are likely formed in the same process solar flares develop.

Although Karoff and his colleagues said our sun is least likely to create a superflare because its magnetic field is not powerful enough, their analysis of other stars suggest that it is not impossible.

"We certainly did not expect to find superflare stars with magnetic fields as week as the magnetic fields on the sun," said Karoff. "This opens the possibility that the sun could generate a superflare – a very frightening thought."

Still, researchers said it is no cause for immediate worry or concern. It is also likely that we would see unprecedented sunspot activity beforehand as a forewarning.

The team's findings are published in the journal Nature Communications.

Photo : NASA Goddard Space Flight Center | Flickr