Let me introduce you to Steve. He’s a bit of a recluse, but really dazzles when he does show up. Perhaps most importantly, he’s actually not a person, but a stripe of purple light in the evening sky. And according to new research, it looks like he has a twin.
The name STEVE is actually an acronym for “strong thermal emission velocity enhancement,” a technical term used to describe this brief purple-pink splash across the sky. Although he might look like one, Steve isn’t an aurora either. He’s pink and purple and only appears briefly, unlike the better known aurora borealis, which usually comes in shades of red, blue, and green and goes on for hours.
Aurorae—including the one that stunned viewers as far south as Florida last month—are generally caused by electrons funneled along Earth’s magnetic field lines into the atmosphere. Steve, however, is his own weird thing: this phenomenon is caused by a rapidly moving stream of ultra-hot gas rushing through Earth’s atmosphere.
In the evening, when Steve shows up, this gas stream is moving westward. Scientists know there’s a similar stream moving eastward in the morning, but hadn’t spotted the corresponding visuals of purple and pink—until now.
An international team of scientists and photographers recently imaged Steve’s long-lost twin: a similar purple streak in the sky that happens at dawn instead of dusk. This discovery, published in the journal Earth, Planets, and Space, continues the mystery of Steve, as scientists are still trying to figure out the exact mechanism that causes these atmospheric lights.
This work “clearly demonstrates that Steve-like emissions are not exclusive to the evening side but also occur on the morning side,” explains Boston University space physicist Toshi Nishimura, who is not affiliated with the new work.
Steve and company are still relatively newly known phenomena—the original Steve was first spotted less than a decade ago in 2016, by the Alberta Aurora Chasers citizen science group in Canada. Steve’s early-riser twin was first noticed by Norwegian photographer Gabriel Arne Hofstra, using a large archive of data available online.
“I developed this website to help photographers and tourists,” explains lead author Sota Nanjo, a space scientist at Japan’s University of Electro-Communications. “It was personally exciting to know that people were actually using it, and that a new aspect of atmospheric phenomena was discovered through it.”
In addition to the twin, Nanjo and collaborators noticed an unexplained patchy glow, “potentially revealing a wider family of Steve,” says Nishimura.
How to see Steve
And if you’re hoping to spot Steve yourself, you might even be able to see him between sunset and midnight if you live in the so-called “subauroral zone,” a little bit south of where you’d traditionally go for the aurora borealis in southern Canada or the northern U.S. “Steve can be seen with the naked eye, but it may look more beautiful when captured by a digital camera,” says Nanjo. “The impression of auroras is very different in photographs compared to seeing them with the naked eye, so I believe the same applies to Steve.”
His twin, on the other hand, is only visible farther north, and between midnight and dawn. “I think the twin’s shy nature, appearing in less populated areas after people have gone to bed, might be why its discovery was delayed compared to Steve,” adds Nanjo.
With this discovery, “citizen scientists have once again spotted something unusual,” says Elizabeth MacDonald, a space plasma physicist at NASA’s Goddard Space Flight Center, emphasizing the role of public participation in this work and her related effort, Aurorasaurus, where you can report any aurorae you see.
“I have confidence that citizen scientists will eagerly keep an eye out now,” she adds, excited to uncover the mysteries of Steve’s entire family and how they can inform our understanding of Earth’s complex atmosphere.
