NASA spacecraft make new discoveries about auroras

NASA's fleet of THEMIS spacecraft, launched less than 8 months ago, has made three important discoveries about spectacular eruptions of Northern Lights (aurora borealis) called 'substorms' and the source of their power.

The discoveries include giant magnetic ropes that connect Earth's upper atmosphere to the Sun and explosions in the outskirts of Earth's magnetic field.

"The satellites have found evidence for magnetic ropes connecting Earth's upper atmosphere directly to the Sun," says Dave Sibeck, project scientist for the mission at the Goddard Space Flight Center. "We believe that solar wind
particles flow in along these ropes, providing energy for geomagnetic storms and auroras."

A "magnetic rope" is a twisted bundle of magnetic fields organized much like the twisted hemp of a mariner's rope. Spacecraft have detected hints of these ropes before, but a single spacecraft is insufficient to map their 3D structure. THEMIS's five satellites were able to perform the feat.

Full story at
http://science.nasa.gov/headlines/y2007/11dec_themis.htm

The Mystery of Auroras
http://www.nasa.gov/mission_pages/themis/
auroras/aurora_feature.html