A mysterious crunch in Earth's magnetic field created a new type of aurora borealis. A NASA intern discovered it.

NASA/JSCThe aurora borealis, or the "northern lights," over Canada is seen from the International Space Station on September 15, 2017.

• A NASA intern discovered a new type of aurora in three-year-old video footage of the Arctic sky.
• Scientists connected the never-before-seen aurora to a huge compression in Earth's magnetic field.
• Video from Norway shows the aurora twisting in unusual patterns as Earth's magnetic field crunches.
• Since there were no eruptions on the sun to push against the magnetic field that day, researchers think the crunch may have come from a storm at the edge of Earth's magnetic bubble.
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A NASA intern has discovered a new type of aurora in three-year-old video footage of the Arctic sky.

With the help of NASA scientists and a satellite, Jennifer Briggs, a physics student at Pepperdine University, connected the unusual aurora to a sudden retreat in Earth's magnetic field. It's the first time scientists have seen an aurora caused solely by a compression of Earth's magnetic field.

Usually, aurorae dance across the sky when lots of high-energy particles from the sun, called solar wind, flood over Earth. But in this case, the sun didn't show any unusual or heightened activity.

Researchers still aren't sure why the magnetic crunch happened, but they think the culprit may have been an unprecedented storm in the region where Earth's magnetic field meets particles from the sun. No one knows where the storm came from or why it caused Earth's magnetic field to shrink so suddenly and rapidly.

Whatever the cause, the mysterious compression produced the stunning, twisting aurora in the video below, which was observed from an island in Norway.

Fred Sigernes/Kjell Henriksen Observatory, Longyearbyen, Norway/Joy NgAll-sky cameras in Longyearbyen, Norway, near the Arctic Circle, captured these images of an unusual, spiraling aurora.

"This motion is something that we've never seen before," Briggs said in a press conference earlier this month. "This eastward and then westward and then spiraling motion is not something that we've ever seen, not something we currently understand."

'Imagine someone punching Earth's magnetic field'

The bright, colorful lights of the aurora come from collisions between electrically charged particles from the sun and gases in Earth's atmosphere, like nitrogen and oxygen. Earth's magnetic field usually deflects these charged particles from the sun, but the field is weaker at the planet's poles. So some particles sneak through, producing the aurora borealis near the north pole and the aurora australis near the south pole.

On the day of this particular aurora, a NASA satellite detected a huge compression in Earth's magnetosphere (the protective bubble that the magnetic field creates around the planet) at the moment the lights began spiraling.

NASAAn animation of the solar wind shows particles streaming from the sun towards Earth.

In just 1 minute and 45 seconds, the edge of the magnetosphere passed the satellite and moved toward Earth's surface, shifting by about 25,000 kilometers (15,000 miles), according to Briggs. That's four times the planet's radius. It would take a commercial jet about 27 hours to fly that distance.

"You can imagine someone punching Earth's magnetic field," Briggs said. "There was a massive, but localized compression."

Jennifer BriggsThis animation shows the compression in the magnetosphere that caused the twisting aurora.

In the above animation, Briggs illustrated the condensing of Earth's magnetic field (the dotted line). The constant stream of solar wind is represented as a solid line.

It was the first time scientists had seen an aurora tied to that kind of crunch in the magnetic field. Scientists still don't know why the magnetosphere compressed so much in such a specific spot in the first place.

Eruptions on the sun can compress Earth's magnetic field, but this was different

A stream of charged particles constantly flows out from the sun and washes over the planets. Sometimes, eruptions on the sun send out sudden rushes of this solar wind, causing an aurora on Earth.

NASAAn explosion of plasma on the sun's surface, called a coronal mass ejection, erupts in 2002.

Though the resulting aurorae are beautiful, the sudden rush of charged particles can interfere with electronic communications, confuse GPS, push satellites out of orbit, endanger astronauts, and even wipe out power grids if the eruption is big enough.

As a rush of solar wind washes past the Earth, it also compresses the magnetosphere, pushing it towards the planet's surface.

In the below video you can see how that works. The color coding is based on the density of plasma - the type of material solar wind is made of. When the steady rush of yellow solar wind suddenly becomes a red-and-orange, plasma-dense flood, it presses against the outer layer of Earth's magnetosphere.

Visualisation by Lutz Rastaetter, Community Coordinated Modeling Center/NASA Goddard Space Flight CenterThis simulation depicts charged solar particles compressing the Earth's magnetosphere after a coronal mass ejection (a huge explosion on the sun), on January 22, 2005.

At the time of the aurora footage that Briggs found, however, there were no solar eruptions that would have caused Earth's magnetic field to suddenly crunch inward.

"The really fascinating thing is that nothing came from the sun to smash into it," she said.

Instead, scientists think the mysterious compression may have come from a storm at the edges of the magnetosphere. They don't know exactly what that might look like or where it could have come from.

"Not only have we never seen a compression of this intensity, we've never even predicted one," Briggs said, adding, "We don't hear about space weather as just normal people, but it can have really incredible impacts."

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