A New Kind of Solar Storm

Next, if the explosion is powerful enough, a billion-ton cloud of gas billows away from the blast site. This is the coronal mass ejection or "CME." CMEs are relatively slow. Even the fastest ones, traveling one to two thousand km/s, take a day or so to reach Earth. You know a CME has just arrived when you see auroras in the sky.

Photographed by Sunspot 720 erupting on Jan. 15th 2005

En route to Earth, CMEs plow through a lot of gaseous material, first in the sun's atmosphere and then out in interplanetary space. You thought space was empty? No. The void between planets is filled with protons and other particles from the solar wind. Shock waves in front of the CME can accelerate these protons in our direction - hence the proton storm.

"CMEs can account for most proton storms," says Lin, but not the proton storm of January 20th. According to theory, CMEs can't push material to Earth quickly enough.

Back to the drawing board: If a CME didn't accelerate the protons, what did?

"We have an important clue," says Lin. When the explosion occurred, sunspot 720 was located at a special place on the sun: 60^o west longitude. This means "the sunspot was magnetically connected to Earth."

more The sun's magnetic field spirals like water from a lawn sprinkler. The field line emerging from solar longitude 60 degrees west usually leads to Earth.

He explains: The sun's magnetic field spirals out into the solar system like water from a lawn sprinkler. (Why? The sun spins like a lawn sprinkler does.)

The magnetic field emerging from solar longitude 60^o W bends around and intersects Earth. Protons are guided by magnetic force fields so, on January 20th, there was a superhighway for protons leading all the way from sunspot 720 to our planet.

"That's how the protons got here," speculates Lin. How they were accelerated, however, remains a mystery.

What does all this mean for astronauts? Stay inside when there's a big sunspot located near solar longitude 60^o W. Or, if you must go moonwalking, take a radiation shelter with you. It's not as hard as it sounds.