Scientists finally find answer to mysterious purple lights called STEVE

15 Mar 2018

STEVE and the Milky Way at Childs Lake, Manitoba, Canada. The picture is a composite of 11 images stitched together. Image: Courtesy of Krista Trinder

An aurora unlike any other – and called STEVE – mystified scientists for the past few years until a recent breakthrough.

The aurora borealis – or the lesser-known aurora australis – are the great stargazing wonders of the world, where Earth’s magnetic field interacts with charged particles from the sun to create a dazzling display of green, red and blue colours in the sky.

However, in 2016, one stargazer in Canada called Notanee Bourassa went out one night and captured an aurora that appeared to be unlike any he had seen before and, as it turns out, many astronomers, either.

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While it looked similar to a typical aurora, this one was purple in colour and lasted for a period of 20 minutes, and was one of 30 other reportedly similar auroras elsewhere.

These reports were taken to a team of citizen scientists called Aurorasaurus, which is funded by NASA and others to track the visual phenomenon.

With no clear idea what they were dealing with, the team settled on the pretty ordinary name STEVE (Strong Thermal Emission Velocity Enhancement) – but new findings show it is anything but ordinary.

By using a series of ground-based, all-sky cameras to snap sweeping vistas of the night sky, researchers from the University of California, Berkeley and the University of Calgary found that STEVE might be an extraordinary puzzle piece, painting a better picture of how Earth’s magnetic fields function and interact with charged particles in space.

In a paper published to Science Advances, the research team said it is very different in structure to typical auroras. Instead of an oval shape, it appears as a line with a defined middle and end.

The mysteries of STEVE

Also, while STEVE goes through the same large-scale creation process as auroras, it travels along different magnetic field lines along much lower latitudes.

That means the charged particles that create STEVE connect to magnetic field lines that are closer to Earth’s equator, hence why STEVE is often seen in southern Canada.

In fact, what proved to be the biggest surprise was that this new aurora wasn’t new at all, and had actually been studied since the 1970s as a fast-moving stream of extremely hot particles called a sub auroral ion drift, or SAID. Until now, scientists didn’t know that it also had an accompanying visual effect.

“STEVE can help us understand how the chemical and physical processes in Earth’s upper atmosphere can sometimes have local noticeable effects in lower parts of Earth’s atmosphere,” said Liz MacDonald, lead of the Aurorasaurus team. “This provides good insight on how Earth’s system works as a whole.”

Colm Gorey was a senior journalist with Silicon Republic