Controlling the speed of solar eruptions

The billion-ton blobs of magnetized gas that the sun sporadically hurls into space have a speed limit, a new study suggests. These solar eruptions, known as coronal mass ejections (CMEs), can’t reach Earth in less than half a day.

SOLAR STORM. Coronal mass ejection (lower right) lifts off from the sun. Disk masks the solar surface; white circle indicates sun’s apparent size. NASA, European Space Agency

That’s important information because CMEs heading toward Earth can harm satellites and interfere with radio communication and power systems. “We now know we have at least 12 hours to take preventive measures,” says Nat Gopalswamy of NASA’s Goddard Space Flight Center in Greenbelt, Md.

Gopalswamy and his colleagues, analyzing CME travel times dating back to 1859, propose that the speed limit comes about because the sun can pack only a limited amount of energy into an individual eruption. Active regions never seem to exceed 20 times the surface area of Earth, and the strength of their magnetic fields also seems to be capped. Gopalswamy presented the study on June 1 at a meeting of the American Astronomical Society in Denver.

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