May 18, 2017: For years, northern sky watchers have occasionally spotted a mysterious ribbon of purple light dancing among the aurora borealis. It was widely called a “proton arc” until researchers pointed out that protons probably had nothing to do with it. So members of the Alberta Aurora Chasers group gave it a new name: “Steve.” Recent widespread reporting about Steve has led to even more sightings–and indeed he appeared just this week over Calgary:
“Steve hung out with me for about 15 minutes on May 17th,” reports photographer Harlan Thomas, who witnessed a spectacular display of auroras over Twisted Ponds. The lights appeared as Earth moved through a stream of fast-moving solar wind that briefly interacted with our planet two days ago.
Steve is still a mystery. No one fully understands the underlying physics of the ribbon. However, one of the European Space Agency’s SWARM satellites recently flew overhead while Steve was active, providing some clues.
“As the satellite flew straight though Steve, data from the electric field instrument showed very clear changes” reports Eric Donovan from the University of Calgary. “The temperature 300 km above Earth’s surface jumped by 3000°C and 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.”
These clues, confirmed and supplemented by similar flybys in the future, may yet crack the mystery of this phenomenon. For now, Steve is unpredictable and may appear in the aurora gallery at any time. Stay tuned!