Science

Purple Streak Named 'Steve' Is a Whole New Type of Aurora

Tuesday, 20 March

 The more familiar auroras, also called Northern and Southern Lights are diffuse, and often mainly green or yellow, sometimes with a purple or pink fringe. Amateur sky watchers brought the east-west oriented streaks to the attention of physicists.

"Steve" was a placeholder name, but stuck, later becoming official, standing for Strong Thermal Emission Velocity Enhancement. Normal auroras follow a cascade of events: charged solar particles hit Earth’s magnetic field, ultimately causing atoms high in the atmosphere to glow. A STEVE happens when plasma—charged, hot particles—flow along the magnetic field’s lines.

STEVEs occur about 100 miles up, 40 miles higher than regular auroras, and are visible beyond the better-known lights’ viewing range. Green bands sometimes seem to shoot out from the purple trunk, much lower in the atmosphere than the main streak. Their cause is unknown. And exactly how do streams of ions become a glowing, purple STEVE? That’s also a mystery.