The citizen scientists were right - mystery light phenomenon STEVE is no aurora

STEVE – not an aurora. Picture: Ryan Sault

  • Amateur photographers snapping light show for decades
  • Scientists only discovered it last year
  • Confirmed STEVE was not an aurora, maybe “entirely new celestial phenomenon”

A spectacular band of light burning through the sky in a 3000° celsius arc that became famous around April last year could be an entirely new celestial phenomenon.

The light show had actually been recorded by amateur photographers for decades.

In the Facebook era, they dubbed the thin ribbons of purple and white light “STEVE”, after the urban hedge given the same name by forest animals in the movie “Over the Hedge”.

Specifically, a group called the Alberta Aurora Chasers had occasionally noticed the bright, thin streams of white and purple light running east to west in the Canadian night sky.

The difference between STEVE and a regular aurora was that STEVE was only visible a few times per year, and closer to the equator than the aurora, which can be seen at any time of the year if all the right conditions are met in the Earth’s ionosphere.

University of Calgary professor Eric Donovan was hosting a talk for the group when he saw a picture of STEVE taken by one member.

He kept in touch with the group, waiting for a moment when a STEVE sighting date coincided with the overpass of one of the European Space Agency’s three Swarm satellites.

Krista Trinder/ NASA Goddard Space Flight CenterSTEVE (Strong Thermal Emission Velocity Enhancement) and the Milky Way at Childs Lake, Manitoba, Canada

Donovan said that just 20 years ago, there was only one sky imager in North America which could be coordinated with sightings.

“Back then we would be lucky if we got one photograph a night of the aurora taken from the ground that coincides with an observation from a satellite,” he said.

These days, there are “more than 100” of those opportunities a night, and when a Swarm satellite was in the right place at the right time, it recorded STEVE as responsible for the temperature 300km above Earth jumping by 3000°C.

“The data revealed a 25 km-wide ribbon of gas flowing westwards at about 6 km/s compared to a speed of about 10 m/s either side of the ribbon,” Donovan said.

STEVE became a celebrity and there are now hundreds of images dedicated to it. Most of which label it an “aurora” or a “new type of aurora”.

But back when it originally became famous, the Aurora Australis Tasmania group, which had been sharing snaps of the phenomenon for years, said it preferred to call STEVE a “proton arc”.

Megan Hoffman/ NASA Goddard Space Flight Center

It usually appeared in a solar storm display, “when the event is waning”, Margaret Sonnemann, author of The Aurora Chaser’s Handbook said.

The scientists got onto the case. In March this year, one team found a stream of fast-moving ions and super-hot electrons passing through the ionosphere right where STEVE was observed.

The researchers suspected these particles were connected to STEVE somehow but were unsure whether they were responsible for producing it.

A follow-up study coordinated ground-based imagery of STEVE with data from NOAA’s Polar Orbiting Environmental Satellite 17, which can measure charged particles precipitating into the ionosphere – the process which causes auroras to appear.

And the POES-17 satellite detected no charged particles raining down to the ionosphere during the STEVE event.

STEVE is definitely not an aurora. In fact, no one knows what STEVE is.

“So right now, we know very little about it. And that’s the cool thing, because this has been known by photographers for decades,” Bea Gallardo-Lacourt, a space physicist at the University of Calgary in Canada and lead author of the new study, said.

“But for the scientists, it’s completely unknown.”

The study’s results suggest STEVE is an entirely new phenomenon. For now, scientists are just calling it “skyglow”.

Here’s a video from NASA showing how STEVE is formed:

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