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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 him from the photos. Unlike the infamous Southern and northern Lights, which blankets the sky in ethereal green swirls near the magnetic poles of the Earth, STEVE appears as a purplish-white ribbon of light that stretches diagonally towards the horizon, stretching hundreds of miles through the atmosphere. It may appear closer to the equator than a typical aurora and is often accompanied by a “fence” of jagged green spikes dancing next to it.
Nobody knows what causes STEVE, but scientists agree it’s not just a simple aurora. Auroras appear when charged particles from the sun sail through space and crack along the lines of the Earth’s magnetic field; STEVE, meanwhile, is a hot, turbulent river of gas that occurs regardless of the solar climate. Researchers suspect it may be the result of a native process in ionosphere – the level of the earth’s atmosphere extending between 50 and 600 miles (80 to 1,000 kilometers) above the earth’s surface, just below that of the planet magnetic field.
Related: Infographic: Earth’s atmosphere, from top to bottom
Now, a new feature of STEVE that appears only in the lower ionosphere causes scientists to question the ethereal lights again. In a study published October 1 in the journal AGU advances, NASA researchers examined hundreds of hours of STEVE footage recorded by citizen scientists to look for a strange new structure they called “the streaks.” These tiny patches of green light are sometimes seen extending horizontally from the bottom of STEVE’s green picket fence, curving back for about 20-30 seconds before disappearing from view.
What exactly are the streaks? As with all things STEVE, nobody really knows. But the new document establishes some basic characteristics. For starters, the long, tube-like appearance of the strips can be an optical illusion; according to the researchers, the stripes act more like tiny points of light, which appear elongated to us due to motion blur.
Each series appears to share a physical connection with the fence structure above it, the team discovered, and each moves along the same magnetic field lines. The streaks also seem picky about where they form; according to the team’s calculations, the stripes appear only low in the ionosphere between 62 and 68 miles (100 to 110 km) above the Earth. This makes the stripes “the smallest optical characteristic of altitude and scale associated with STEVE,” the researchers wrote in the study.
A clue to the origin of the stripes comes from their green color, which is identical to the color of STEVE’s fence. According to the researchers, this particular green wavelength is associated with atomic emissions oxygen in the atmosphere. Turbulent particles inside STEVE are likely to collide and rapidly heat ambient oxygen, the team wrote, creating small green fires in the sky that flow under the fence as they slowly die out.
Or maybe not. STEVE’s series are so new to science that this paper is probably just “the tip of the iceberg,” study co-author Elizabeth MacDonald, a space scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, he said in a statement. That depth of uncertainty is normal when it comes to STEVE, which was first reported by citizen scientists watching Canadian skies in July 2016. Astronomers continue to rely on the observations of civilian photographers and astronomers, whose time and whose passion can overcome the scientists’ – in order to decompress the mysterious river of light in our atmosphere.
Originally published in Live Science.
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