To reach Steve’s place, turn south at the northern lights

For years, sky gazers in Canada have been training their camera lenses on a wispy strand of purple light running across the country from east to west, sometimes flanked by neon green fingers that appear to wave.

It looks like a piece of the aurora borealis, or the northern lights: blushes of pink or green that illuminate the night sky at high latitudes, caused by solar particles interacting with the Earth’s magnetic field. But this strip of light is different. It has always appeared farther south, beyond the bounds of normal aurora sightings.

Amateur aurora watchers have taken hundreds of photographs of this adjacent phenomenon, often drawing out its fluorescent colours with long exposures or photo editing. They called it Steve, as a sort of placeholder until a more formal name can be found.

Now a research paper has shed light on what Steve actually is, and scientists have proposed a moniker: Strong Thermal Emission Velocity Enhancement. So, it’s still Steve. But as a “bacronym” – a retroactive acronym.

The paper, published in Science Advances, a peer-reviewed journal from the American Association for the Advancement of Science, suggests that Steve has a lot in common with a phenomenon called a “subauroral ion drift”, or SAID, in which ions flow very quickly from east to west, closer to the equator than the aurora borealis.

Like the northern lights, SAID results from interactions between charged solar particles and the Earth’s magnetosphere.

“It’s something that we know that’s actually been studied for 40 years,” says Elizabeth A MacDonald, a space physicist at Nasa’s Goddard Space Flight centre who led the paper’s research team. “But they have never been seen to have this optical component.”

In other words, SAID usually looks nothing like Steve, with its long purplish streak and green fingers. That leaves many questions unanswered, and scientists are still working on those.

MacDonald and others worked with data from Swarm, a constellation of satellites run by the European Space Agency, and learned that Steve is a strip of ionised gas as hot as the Earth’s core and moving through the air at around 4 miles per second.

Further research revealed that Steve was similar to a sub-auroral ion drift.