First look at an electron dance.

First look at an electron dance

The data that electrons can become trapped on the lines of a planet's magnetic field and spiral around them, at the same time speeding back and forth between the northern and southern hemispheres along the lines, has for years been a familiar phenomenon in theory and in laboratory demonstrations. Now a group of scientists has obtained what they describe as the first images of such a spiral glowing around one of Earth's own magnetic field lines.

In a project called Echo 7, last in a series that began in 1970, a NASA sounding rocket soared aloft from the Poker Flat Research Range in Alaska on Feb. 8. Among the payloads deployed from the rocket during the complex mission was an electron-beam "gun" developed by a team under Perry R. Malcom of the Air Force Geophysical Laboratory at Hanscom Air Force Base in Massachusetts. Also deployed was a low-light television camera, which recorded the images produced as the geomagnetically trapped and spiraling electrons fired in pulses by the gun ionized neutral atoms of the upper atmosphere.

The images, says principle investigator John R. Winckler of the University of Minnesota in Minneaplis, initially showed a diffuse, essentially cylindrical glow as the rocket descended to an altitude of about 120 kilometers from 290 km, with the spiral structure becoming most clearly visible between about 100 and 90 km.

The Echo project is so named because its overall purpose is the study of phenomena such as the aurora borealis and Earth's Van Allen trapped-radiation belts, associated with particles "echoing" alnog the magnetic field lines between north and south.