There's a light in the night sky over Canada that's puzzling scientists. It looks like a white-purple ribbon. It's very hot, and doesn't last long. And it's named STEVE.
STEVE: as in, Strong Thermal Emission Velocity Enhancement.
Scientists don't actually know what's causing the atmospheric phenomenon, which has been known to amateur photographers of the night sky for decades but only recently came to the attention of researchers.
But in research published this week in Geophysical Research Letters, they pin down what it definitely isn't. It's not an aurora.
An aurora is a phenomenon that causes parts of the sky at high latitudes to glow colors such as green, blue or red. It has to do with electrons and protons from a region around the Earth called the magnetosphere.
"These charged, energetic particles sometimes are able to rain down into the Earth's upper atmosphere, and when they do they produce these displays of colors that we call an aurora," says Bea Gallardo-Lacourt, a space physicist at the University of Calgary who is one of the authors of the study.
So, the researchers set out to figure out whether STEVE is caused by particle precipitation, the main hallmark of an aurora.
They searched satellite data archives for an instance when a satellite was crossing an area experiencing STEVE, and found a good example from a NOAA satellite during an event in eastern Canada in March 2008.
"We didn't see any evidence of these particles," Gallardo-Lacourt said. "So that gave us a clue that STEVE might not be produced in the same sense that an aurora is produced."
The study concludes that STEVE is "clearly distinct" from an aurora and "its skyglow could be generated by a new and fundamentally different mechanism in the ionosphere."
STEVE has more mysteries. She says it's unclear what produces STEVE, which is within a stream of very fast-moving and hot gas. The scientists want to take spectrographic measurements of STEVE, which will help them to figure out the altitude in the atmosphere where it forms.
And STEVE appears at lower latitudes than auroras do, Gallardo-Lacourt says, but auroras and STEVE may still have a relationship. She notes that STEVE is "usually associated with a lot of auroral activity at higher latitudes, so one of the questions that we are evaluating is how the activity happening at higher latitudes can help the ionosphere to create the correct conditions for STEVE to form."
Gallardo-Lacourt says the scientific community learned about STEVE when a NASA scientist was chatting in 2016 with a group of amateur photographers called the Alberta Aurora Chasers.
The aurora chasers had been calling the phenomenon a "proton arc," which the scientists thought was not an accurate description. So they asked the aurora chasers to pick a different name, and they settled on "Steve."
Before it was an acronym, it was a reference to a scene in the 2006 children's movie Over the Hedge.
In it, a group of animals stand dumbfounded next to what to them is another awe-inspiring phenomenon – a garden hedge.
"What is this thing?" one creature says. "I'm scared," another mutters.
"I'd be a lot less afraid of it if I just knew what it was called."
A squirrel blurts out: "Let's call it Steve." The animals breathe a sigh of relief.
"I love the name," says Gallardo-Lacourt. "It shows the connection between citizen scientists and the formal scientists."
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