On March 1, 2010, the Kepler space telescope spotted a distant star brighten slightly. Compared with the ferocious intensity of a supernova or gamma-ray burst, this event was feeble. It was merely a stellar flare, and by no means the most powerful flare ever seen. Nevertheless, it was ominous. Fig. 1. One of the largest flares ever seen on the Sun—captured here in extreme ultraviolet light by the Solar and Heliospheric Observatory—erupted in November 2003. Classed as an X28 flare, it had greater energy than any other flare seen in the space exploration era but still falls far short of a superflare. Image credit: SOHO/EIT (ESA and NASA). The star, known as KIC9944137, lies more than 1800 light-years away between the constellations Cygnus and Lyra. It closely resembles our Sun: about the same size, about the same temperature, about the same rotation rate. Yet the flare was at least 10 times as powerful as anything recorded on the Sun. Kepler has detected many more such superflares on sunlike stars. In May this year, a team of astronomers led by Yuta Notsu of Kyoto University in Japan published a study confirming that many of these stars share our Sun’s composition and other properties (1). This raises the prospect of superflares on the Sun, perhaps one every few centuries. Such events could have serious consequences for society. But other evidence for these events is strangely lacking. They should deposit much more radioactive material on Earth and the Moon than researchers have found thus far. Either our Sun is subtly different from these superflare stars, or a superflare is possible in the foreseeable future. Flares happen because of convulsions in the Sun’s magnetic field. The field stretches out through the solar atmosphere and into deep space. Electromagnetic forces fuse the field to the electrically …