The mysterious, aurora-like phenomenon called STEVE just got a little weirder.
If you don’t know STEVE (short for Strong Thermal Emission Velocity Enhancement) by name, you may know it from photos. Unlike the infamous Southern and Northern Lights, which blanket the sky in ethereal green swirls near Earth’s magnetic poles, STEVE appears as a purplish-white ribbon of light that slashes diagonally toward the horizon, stretching hundreds of miles through the atmosphere. It can appear closer to the equator than a typical aurora, and is often accompanied by a “picket fence” of jagged green points dancing beside it.
Nobody knows what causes STEVE, but scientists agree it’s no mere aurora. Auroras appear when charged particles from the sun sail across space and crackle along Earth’s magnetic field lines; STEVE, meanwhile, is a river of hot, turbulent gas that shows up independently of that solar weather. Researchers suspect that it may be the result of some native process in the ionosphere — the level of Earth’s atmosphere that extends between 50 and 600 miles (80 to 1,000 kilometers) above Earth’s surface, just below the planet’s magnetic field.
Now, a newfound feature of STEVE that only appears in the lower ionosphere has scientists puzzling over the ethereal lights again. In a study published Oct. 1 in the journal AGU Advances, NASA researchers reviewed hundreds of hours of STEVE footage recorded by citizen scientists to look for a strange new structure they’ve named “the streaks.” These tiny smears of green light are sometimes seen extending horizontally from the bottom of STEVE’s green fence pickets, curving backward for about 20 to 30 seconds before vanishing from view.