The group of Borealis enthusiasts, known as the Alberta Aurora Chasers, were recently combing through old photos of their favorite light phenomenon when they came across a few images of something they had not noticed before. Several of their photos had a bright purple streak that had not yet been identified. They have chosen to call this new phenomenon “Steve”.
What is Steve?
The AAC is a Facebook page that attracts membership interested in the night sky, especially the Aurora Borealis. They take photographs of an atmospheric phenomenon and share them on the page. Many of the photos are viewed by experts in the field, who also share the amateur’s passion. One of those experts is Eric Donovan from the University of Calgary.
While looking through the photos one evening, Donovan discovered the strange arc of purple light. He had not noticed it before in pictures. It reappeared in several other photographs taken by the group. The AAC had been referring to the atmospheric phenomenon as a “Proton Arc”. Donovan was not so sure, and in order to confirm his suspicions, he was able to use the European Space Agency’s Swarm satellites. This is a trio of devices in orbit that examine Earth’s magnetic field.
He discovered that the event is due to a sudden change in temperature far above the Earth’s surface, almost 3000 degrees Centigrade. This causes the gasses in the air beneath it to travel at speeds close to six kilometers per second, as opposed to the ten meters per second of the surrounding gasses. It also creates the purple streak, which Swarm has recorded several times since then.
“It turns out that Steve is actually remarkably common, but we hadn’t noticed it before.”