Astrophysicist Spiro Antiochos describes the fast CME of November 6, 1997, and its impact on the SOHO spacecraft.

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Sun-Earth Connection Continued

The CME on November 6, 1997, was the fastest and most energetic one yet observed with SOHO. The image above (left) shows the CME exploding at a speed of approximately 4.5 million miles per hour. This CME produced an intense radiation storm of high-energy protons that hit SOHO and caused the ''blizzard'' that appears in the image (right). To view a QuickTime movie of this event, make a selection below. (1 meg) (700k)

What Causes CMEs?

The sun is constantly kicking out material from its atmosphere, generating what's known as the solar wind. The solar wind travels through space and is usually deflected by the earth's magnetosphere. Compared to the gentle breeze from the solar wind, fast-moving CMEs are a hurricane of plasma and coiled magnetic field lines spinning through space. Until recently, scientists didn't know what caused these violent magnetic eruptions.

Normally, magnetic field lines move up through the sun slowly, at about one mile a second. This slow, continuous movement creates the solar wind. When a CME takes off, however, it can move thousands of miles a second. The mystery, says astrophysicist Spiro Antiochos, is: What allows a CME to build energy in the sun's atmosphere until it bursts through in a violent explosion?

A new theory, developed by Antiochos and colleagues at the Naval Research Lab, involves competing magnetic field lines that hold down the developing CME like tethers hold down an expanding helium balloon. Antiochos compares these tethering field lines to rubber bands that can stretch but never break. Through a process called magnetic reconnection, opposing magnetic field lines merge and cancel. Then, with no tether holding the ballooning material in place, the CME erupts out of the sun's atmosphere.

The longer magnetic fields keep the CME pinned down, the more energy it builds and the faster and more violent the explosion when it's finally set free. Fast CMEs can reach speeds of 1250 miles per second and eject a billion tons of hot, ionized gas into space.