‘STEVE’: the mysterious lights in the sky

South of the northern lights, there lies another aurora-like phenomenon: STEVE (or Strong Thermal Emission Velocity Enhancement, formally). It’s distinguished by a large, purple stream of plasma.

One of the many unique things about STEVE is its accompanied ‘picket fence’. Vertical green stripes line the purple ribbon, and these have some mystery surrounding them.

STEVE and its vertical streaks of green. Image credit: Rocky Raybell

Due to visual similarities that the stripes have with aurora borealis, scientists thought at first that they could be a type of aurora.

However, auroras are created when the sun’s solar wind gets into our atmosphere and collides with the oxygen and nitrogen from Earth’s atmosphere.

STEVE’s river of plasma and streaks of green lack the evidence of nitrogen emission required for an aurora, and show up regardless of solar weather.

Another possibility considered is that STEVE is a form of airglow, the atmospheric emission that causes the night sky to never be truly dark. It can also create bright swathes of colour.

“STEVE in general appears to not conform well to either one of those categories,” Joshua Semeter, a professor at Boston University and author on a paper for AGU Advances, said. “The emissions are coming from mechanisms that we don’t fully understand just yet.”

To mystify the light show further, horizontal streaks can be spotted tailing the vertical ones. According to the paper, the particular green seen in the picket fence is associated with emissions from atomic oxygen in the atmosphere. It’s possible that the plasma within STEVE is colliding with that oxygen, heating it up and creating green fires in the sky.

The horizontal streaks behave more like single points of lights affected by motion blur, rather than extensions of the vertical ones.

This would explain why the branches appear for about 20 to 30 seconds at a time before disappearing. Despite how cool “green fire in the sky” sounds, the unfortunate – but exciting – truth is that we simply don’t know.

STEVE’s streaks are a new anomaly that we’re only just beginning to tackle.

“This paper is the tip of the iceberg,” Elizabeth MacDonald, a space scientist at NASA’s Goddard Space Flight Center said.

Much of the information on the topic has been uncovered by citizen scientists. The first photo of STEVE that sparked researcher interest was taken by Neil Zeller, a man who was just intrigued by the beauty of the light show. Years later, and he’s co-authoring a scientific paper on it.

The beauty of science is that there is always something that is undiscovered, and with phenomenon such as this, anyone can contribute.

Featured image: Krista Trinder

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