Computer Simulation Solves Space Mystery

Article excerpt

A mysterious phenomenon detected by space probes has been explained by a massive computer simulation precisely aligned with spacecraft observations. Besides solving an astrophysical puzzle, the simulation findings might also lead to better predictions of high-energy electron streams in space that could damage satellites.

The simulation shows that an active region in Earth's magnetotail--a vast and intense magnetic field swept outward from Earth by the solar wind--is roughly 1,000 times larger than had been thought. This means a volume of space energized by "reconnection" events is sizeable enough to explain the large numbers of high-speed electrons detected by a number of spacecraft missions, including the Cluster mission.

Jan Egedal, an associate professor of physics at the Massachusetts Institute of Technology (MIT) and a researcher at the Plasma Science and Fusion Center, working with MIT graduate student Ari Le and William Daughton of the Los Alamos National Laboratory (LANL), report on this solution to the space conundrum in a paper published in the journal Nature Physics.

Egedal explains that as the solar wind stretches Earth's magnetic field lines, the field stores energy like a stretched rubber band. When the parallel field lines suddenly reconnect, they release that energy--like releasing the rubber band. This propels electrons with great energy (tens of thousands of volts) toward Earth, where they impact the upper atmosphere. This impact is thought, directly or indirectly, to generate the glowing upper-atmosphere plasma called the aurora, producing spectacular displays in the night sky.

What had puzzled physicists is the number of energetic electrons generated in such events. According to theory, it should be impossible to sustain an electric field along the direction of the magnetic field lines, because the plasma (electrically charged gas) in the magnetotail should be a near-perfect conductor. But such a field is just what's needed to accelerate the electrons. And, according to the new simulation, the volume of space where such fields can build up can, in fact, be at least 1,000 times larger than theorists thought possible--and thus large enough to explain the observed electrons. …