While the northern and southern lights have dazzled watchers of the night sky for millennia, vigilant citizen scientist photographers found another type of aurora over the past few years: a short-lived shimmering purple ribbon of plasma. Their intriguing discovery drew the attention of space scientists, who have just begun to study them.
“Dedicated aurora chasers, especially from Alberta, Canada, were out in the middle of the night, looking north and taking beautiful photos. Then farther south they happened to see a faint narrow purple arc as well,” says Elizabeth MacDonald, a space physicist at NASA Goddard Space Flight Center in Greenbelt, Maryland. There’s different physics behind those purple aurora, she says.
MacDonald led a team who observed the aurora by sending one of the European Space Agency’s Swarm satellites through it. The results suggest they’re a manifestation of accelerated and heated charged particles coming from the sun that interact with a particular part of the Earth’s magnetic field in the ionosphere. The team published their findings in Science Advances Wednesday.
The citizen scientists weren’t sure about what they’d seen, so they called the strange aurora structure “Steve.” The name caught on, and MacDonald and her team kept it, proposing the backronym Strong Thermal Emission Velocity Enhancement (STEVE). While scientists had known about lower-latitude currents of charged particles for decades, they had no idea that they could produce auroras visible to the eye. But now that people have smartphones and digital cameras more sensitive than what scientists had back then, they can pick out these rare aurora, which last only about an hour.
What Makes STEVE Unique?
As opposed to a red, green, or yellow aurora with a wispy, curtain-like shape (see photos), STEVE appears as a ribbon across the sky in a mauve or purplish color. It’s sometimes combined with unstable, smaller green picket fence-like features. In the past, some people mistakenly called these aurora phenomena “proton arcs,” but STEVE is narrower and with clearer structure to it.
Instead, MacDonald and her colleagues associate STEVE with something called “subauroral ion drift.” This happens farther south, at about 60 degrees above the equator, where the alignment of the global electric and magnetic fields makes ions and electrons flow rapidly in the east-west direction, heating them in the process. The aurora seem to be seasonal, not appearing in winter, and they coincide with space weather—charged particles spewed out by the sun.
“Because this is a new way of observing a phenomenon linked to space, it provides a new way to study it,” says Vassilis Angelopoulos, a space physicist at UCLA not involved in the study. “Citizen scientists can also be involved in triangulating them and determining their altitudes.” (Learn what happens when the Earth’s magnetic pole switches.)
Now with more interest in these aurora, MacDonald and other scientists plan to study them further to figure out what’s causing them, while citizen scientists will be on the lookout. They can continue to play a role, because if they glimpse one from different locations, scientists can use those observations to infer where and how high up it is.
Amateur astronomers can try to spot one in northern regions like Alberta, Montana, or Michigan, or in the southern hemisphere in New Zealand. MacDonald suggests downloading the app for her citizen science project, Aurorasaurus, which alerts people when the aurora are seen.
Citing a similarity to the rich history of contributions from citizen scientists in ornithology, MacDonald adds, “Finding STEVE is like discovering a new species of bird.”