‘Steve' Is a Radiant Purple Sky Ribbon That Defies Explanation

A new study confirms that Steve is not generated by particle precipitation. So what is powering this skyglow?

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Aug 21 2018, 6:30pm

Image: Krista Trinder

You may have met people named Steve in your life, but have you met the radiant ribbon of colorful light in the night sky named Steve? This unexplained phenomenon looks deceptively similar to an aurora and is observed at the same high latitudes in both hemispheres where you’d expect to see magnetic light shows.

Named by Calgary-based photographer Chris Ratzlaff—it’s a nod to the 2006 film Over the Hedge, which classifies “the unknown” as “Steve”—this ribbon appears to be made of hot gas, in the range of 3,000°C (5,430°F). It forms 450 kilometers (280 miles) above Earth’s surface.

Once scientists started studying Steve in 2016, they gave it an official backronym: Strong Thermal Emission Velocity Enhancement. Despite its visual similarity to auroras, research published Monday in Geophysical Research Letters confirms that Steve is generated by a different, unexplained process.

Led by Bea Gallardo-Lacourt, a space scientist at the University of Calgary, the new study focuses on a Steve sighting that occurred on March 28, 2008. This appearance was fortuitously chronicled by the ground-based component of NASA’s THEMIS mission (called All‐Sky Imagers), as well as NOAA’s Polar Orbiting Environmental Satellite (NOAA-17), which was overhead as Steve shone.

Light from auroras is caused by particle precipitation, which occurs when high-energy charged particles cascade into the upper atmosphere along Earth’s magnetic field lines. No such high-energy precipitation was observed from the 2008 event. While there was an observed flux of lower-energy particles, that does not explain the vibrancy of Steve’s luminosity and color. By combing through data captured from above and below the purple and green ribbon, the authors concluded that the “skyglow could be generated by a new and fundamentally different mechanism in the ionosphere.”

In addition to arranging more of these multi-perspective observations of Steve, Gallardo-Lacourt and her colleagues are planning to publish more studies about Steve’s known proclivities, like where and when it commonly shows up.

Read More: On Mars, a Brilliant Blue Aurora Colors the Night Sky

“Probably the most important question to answer now is: if Steve is not produced by precipitating particles (like aurora), how is the structure being created?” Gallardo-Lacourt told me in an email. “To answer this we need simulations (modeling the physics involved) that could help us understand all the dynamics that are playing a role.”

She added that the research that has been published about Steve so far is “just the initial steps of a really exciting research topic that has many open questions.”

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