have together stumbled on the ultimate electron beam, a spike of energy that shot into space high above Earth and left a hole in the sky.If the discovery stands, it could help scientists understand the space electronics involved in turning on colorful night-sky lights known as aurora.
A study based on data produced by a team of Earth-orbiting satellites that make up the European Space Agency's Cluster mission is being presented today at a meeting of the American Geophysical Union and will be detailed in the Dec. 13 issue of the journal Nature.
Like a florescent light
Aurora are wild sheets and filaments of colorful light that grace the night sky for residents of the far northern and southern parts of Earth. Also known as the Northern or Southern Lights, the illumination is driven by the Sun's energy. The basic mechanisms behind the phenomenon are understood: Think of typical office lighting.
"In a florescent light tube, the inside is a near vacuum," explains Patrick Newell, a Johns Hopkins University scientist who was not involved in the research but analyzes it in an accompanying article in Nature. "An electric field (the voltage from your wall socket) is applied across the ends. The electric field accelerates electrons, that then strike the small amount of gas inside, giving off light."
Aurora are generated in a near-vacuum, too. Electrons flung earthward by the Sun strike a few atoms in the planet's very thin upper atmosphere. The atoms are excited and give off light.
"The difference of course is that there is no wall socket to supply the electric fields," Newell said. "So we have to understand where these electric fields come from, and how they are maintained."
The new findings may help.
A study of the Cluster data, led by Goran Marklund of the Royal Institute of Technology in Stockholm, found that an upward-moving beam of electrons grew and then vanished within a period of time that lasted just over 3 minutes.
Hole in the sky
The activity took place in a layer above Earth called the ionosphere, where electrons roam freely after being split up by solar energy. The ionosphere starts about 30 miles up (50 kilometers) and ranges up to more than 620 miles (1,000 kilometers). Radio waves can be bounced off the ionosphere to enable long-distance transmissions.
The electrons spotted by Cluster were evacuated into space, the researchers say, leaving a hole in the ionosphere.
Marklund and his colleagues suggest that the electron beam allowed a corresponding downward beam to develop, which led to visible aurora.
"The findings suggest an explanation for why the cold background electrons in space do not short out the electric field that causes the aurora: because they are drained away first," Newell said.
But Newell cautioned that the encounter was with "a very unusual auroral structure, at very high altitudes. So there is some question about how typical this event is." A proper study of the phenomenon would require a similar multi-craft mission dedicated to the task at a lower altitude, he said.
The observations were made over Earth's north polar region Jan. 14, 2001. The Cluster satellites orbit Earth at different altitudes, ranging from 124 miles (200 kilometers) to 11,600 miles (19,000 kilometers) up.
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