Solar flares on the sun frequently shower Earth with high-energy particles causing the Aurora Borealis and, occasionally, less-welcome disruptions to power networks and communications. But researchers say that there is a chance—though small—that the sun could one day blast us with a solar flare thousands of times as powerful, potentially frying our atmosphere and obliterating life. Other stars occasionally produce such “superflares,” some up to 10,000 times the power of the largest solar flare ever detected. To see whether these are generated by the same process as happens on the sun—the breaking and reconnection of magnetic fields (pictured above)—astronomers studied light from 100,000 stars using China’s Guo Shouiing Telescope. As they report online today in Nature Communications, superflares do seem to be produced by the same process, but they usually occur in stars with much stronger magnetic fields than the sun’s. Still, the researchers found that about 10% of the superflaring stars had magnetic fields similar to or weaker than the sun’s. From evidence in tree rings, the researchers say, it looks like Earth suffered small superflares—10 to 100 times bigger than normal—in 775 C.E. and 993 C.E. We can expect more, they conclude, once per millennium. (As for the chances of an Earth-frying flare, they don’t say.) So, back up your data and stock up on candles.