Understand how big solar flares can be


To be clear, Proxima Centauri is not like the Sun. It’s a dwarf M, a little orb that glows red. And these little stars are famous for their oversized flares. But some solar stars can also send super flares.

This achievement came from telescopes in space designed to search for planets around other stars. NASA’s now defunct Kepler Telescope did this by looking for subtle hollows in starlight as planets passed in front of their sun.

Over four years, Kepler recorded 26 super flares – up to about 100 times more energetic than the Carrington event – on 15 solar stars, researchers reported in January. NASA’s ongoing TESS mission, another space telescope searching for exoplanets, found a similar frequency of superflares on sun-like stars in its first year of operation.

Kepler’s data imply that sun-like stars experience the most powerful of these eruptions about once every 6,000 years. Our Sun’s strongest eruption during this time is an order of magnitude smaller – but could a super eruption occur in our future?

“I don’t think a theory has enough predictive power to mean anything,” says Hudson. “The dominant theory basically says that the larger the sunspot, the larger the eruption.” Sunspots mark where the Sun’s magnetic field crosses its surface, preventing hot gas from bubbling up from below. The place looks dark because it’s cooler than everything around it.

And that’s a difference between the Sun and its eruptive neighbors. Super flares seem to occur on stars with dark, cold spots much larger than ever before on the Sun. “So based on the known spot areas, there would be a limit,” says Hudson.

The intricacies of the magnetic machinations of any star – spots, flares, etc. – are still poorly understood, so tying all of these observations into one cohesive story will take time. But the quest to understand all of this could improve predictions of what to expect from the sun in the future.

Flares powerful enough to disrupt our power grid likely occur, on average, a few times a century, says Love. “Looking at 1859 helps put things in perspective, because what has happened in the space age since 1957 has been more modest. The Sun hasn’t sent us a Carrington-type flare for a while. A repeat of 1859 in the 21st century could be disastrous.

Mankind is much more dependent on technology than it was in 1859. An event similar to Carrington’s today could wreak havoc on power grids, satellites and wireless communications. In 1972, a solar flare destroyed long-distance telephone lines in Illinois, for example. In 1989, an eruption extinguished most of the province of Quebec, cutting power to about 6 million people for nine hours. In 2005, a solar storm disrupted GPS satellites for 10 minutes.

The best prevention is prediction. Knowing that a coronal mass ejection is on the way could give operators time to reconfigure or safely shut down equipment to prevent destruction.

Building additional resilience might also help. For the power grid, this could include adding redundancy or devices that can drain excess load. Federal agencies could have a stockpile of mobile power transformers ready for deployment in areas where existing transformers – which melted in previous solar storms – have been destroyed. In space, satellites could be put into safe mode while they wait for the storm to end.

The Carrington event was not a one-off event. It was just a sample of what the sun can do. If research into past solar flares has taught us anything, it’s that humanity shouldn’t be wondering if a similar solar storm could reoccur. All we can ask ourselves is when.

This article originally appeared in Known magazine, an independent journalistic company of Annual Reviews. Subscribe to bulletin.

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