Citizen scientists help solve mystery of the purple sky

"People have studied a lot of SAIDs, but we never knew it had a visible light," researcher Eric Donovan said.

By Brooks Hays

March 14 (UPI) -- The aurora borealis has a cousin, a related geomagnetic phenomenon, and citizen scientists helped discover it.

In 2015 and 2016, citizen scientists reported seeing a mysterious purple light dance across the sky some 30 times. The reports were filed by participants of Aurorasaurus, an online project funded by NASA and the National Science Foundation.


Aurorasaurus links backyard skywatchers with trained astronomers as part of an effort to track auroras, the colorful light shows produced when high-energy particles from sun penetrate Earth's magnetosphere and collide with gas molecules in the upper atmosphere.

But as NASA scientists realized, Aurorasaurus participants were witnessing a phenomenon unique from the typical aurora.

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The average aurora takes on an oval shape and features blues, greens and reds. The phenomenon documented by several citizen scientists glowed purple and took on a linear shape, with a beginning and an end. The purple ribbon, or line, is often underlined by a picket fence-like green glow. The average aurora lasts hours, but the mystery aurora usually only lasted around 20 minutes.

To stir up additional interest among Aurorasaurus participants, scientists gave the phenomenon an unusual name -- Steve.

While backyard astronomers documented Steve's whereabouts, scientists used ground telescopes to capture photographs of large swaths of the sky, securing several shots of Steve. At the same time, the European Space Agency's Swarm satellite documented Steve from above.

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Both the reports of citizen scientists and the telescope photos confirmed that Steve tends to appear at lower latitudes, which explains why it is mostly spotted in Southern Canada.

The satellite data linked Steve with a phenomenon known as a sub auroral ion drift, or SAID, a string of high-energy particles that flows along magnetic field lines in the sub auroral zone, lines close to the equator.

"People have studied a lot of SAIDs, but we never knew it had a visible light," Eric Donovan, a researcher at the University of Calgary, said in a news release. "Now our cameras are sensitive enough to pick it up and people's eyes and intellect were critical in noticing its importance."

But while Steve may exist at lower latitudes than the aurora borealis, they typically appear together, suggesting a link between the higher latitude auroral zone and lower latitude sub auroral zone. Scientists suggest additional analysis of Steve could help researchers better understand the interactions between solar particles and Earth's electromagnetic fields.

The most recent analysis of Steve was published this week in the journal Science Advances.

"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, a space scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "This provides good insight on how Earth's system works as a whole."


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