Powerful radio waves generated by navigational beacons are causing "electron rain" to fall into Earth's upper atmosphere from the Van Allen radiation belts thousands of miles out in space, a team of researchers from four universities has found.

No one knows whether the effects are harmful, but they are thought to be the first "environmental" effects in space traceable to human activities on Earth.

The Van Allen belts are vast magnetic fields that loop Earth from pole to pole. If Earth were a marble, the belts would fill the size and shape of a doughnut, with the marble in the hole. The magnetism traps a barrage of subatomic particles, chiefly protons and electrons, flowing through space as part of the solar wind.

Because the particles are charged and have high energy, they are a potentially dangerous form of radiation that space travelers must avoid. The particles are also a source of beauty because, as they flow down toward the poles, they cause atoms in the air to glow as an aurora.

Last summer, Cornell University engineer Paul Kintner led a search for effects on the Van Allen belts of the low-frequency radio waves from radio transmitters used as navigational beacons. These, including one in Annapolis, dot the planet and are relied on by ships and planes.

The group launched a sounding rocket from Wallops Island, Va., that rose about 257 miles in a 10-minute flight. Near its highest point, detectors in the nose cone revealed showers of electrons raining in patterns correlated with beacons from the transmitters and with lightning bolts, which produce the bursts of random radio signals known as static.