July 24, 2008: Duck! Plasma bullets are zinging past Earth.
http://science.nasa.gov/headlines/y2008 ... ?list71415
That's the conclusion of researchers studying data from NASA's five THEMIS spacecraft. The gigantic bullets, they say, are launched by explosions 1/3rd of the way to the Moon and when they hit Earth—wow. The impacts spark colorful outbursts of Northern Lights called "substorms."
An artist's concept of the THEMIS satellites lined up inside Earth's magnetotail with an explosion between the 4th and 5th satellites.
The discovery came on what began as a quiet day, Feb 26, 2008. Arctic skies were dark and Earth's magnetic field was still. High above the planet, the five THEMIS satellites had just arranged themselves in a line down the middle of Earth’s magnetotail—a million kilometer long tail of magnetism pulled into space by the action of the solar wind.
That's when the explosion occurred.
A little more than midway up the THEMIS line, magnetic fields erupted, "releasing about 1015 Joules of energy," says Angelopoulos. "For comparison, that's about as much energy as a magnitude 5 earthquake."
Although the explosion happened inside Earth's magnetic field, it was actually a release of energy from the sun. When the solar wind stretches Earth's magnetic field, it stores energy there, in much the same way energy is stored in a rubber band when you stretch it between thumb and forefinger. Bend your forefinger and—crack!—the rubber band snaps back on your thumb. Something similar happened inside the magnetotail on Feb. 26, 2008. Over-stretched magnetic fields snapped back, producing a powerful explosion. This process is called "magnetic reconnection" and it is thought to be common in stellar and planetary magnetic fields.
The blast launched two "plasma bullets," gigantic clouds of protons and electrons, one toward Earth and one away from Earth. The Earth-directed cloud crashed into the planet below, sparking vivid auroras observed by some 20 THEMIS ground stations in Canada and Alaska. The opposite cloud shot harmlessly into space, and may still be going for all researchers know.
"For the first time, THEMIS has shown us the whole process in action—from magnetic reconnection to aurora borealis," says Sibeck. "We are finally solving the puzzle of substorms."
The THEMIS mission is scheduled to continue for more than another year, and during that time Angelopoulos expects to catch lots more substorms--"dozens of them," he says. "This will give us a chance to study plasma bullets in greater detail and learn how they can help us predict space weather."
"THEMIS is not finished making discoveries," believes Sibeck. "The best may be yet to come."
Great, man...Truly great...
