Entirely New Type of Aurora Discovered, With Waves of Oxygen Atoms Creating 'Dunes' in the Night Sky

Researchers have discovered an entirely new type of aurora that produces "dunes" in the night sky.

Aurorae—which was identified with the help of citizen scientists in Finland—is thought to be produced when streams of charged particles emitted by the sun come into contact with waves of oxygen atoms in Earth's upper atmosphere, making them glow.

"Aurora in general are produced when electrons precipitating from outer space collide with atmospheric molecules and atoms, which are excited," Minna Palmroth from the University of Helsinki told Newsweek. "The release of this excitation state is the auroral light."

"The same mechanism is in neon lamps—there, the electric current excites neon gas and the excitation state is released as neon light," she said. "So you can say that aurora are celestial neon lamps due to the same mechanism."

The "dunes" can be found at an altitude of around 62 miles in the upper part of the third atmospheric layer known as the mesosphere, according to a study describing the phenomenon in the journal AGU Advances. They consist of an even pattern of waves, like dunes on a sandy beach, with a bright green color.

Palmroth and colleagues say that a special type of atmospheric gravity wave—ripples in the sky formed when buoyancy pushes air up, and gravity pulls it back down—are crucial to the formation of the novel aurora.

This special and rare form of an atmospheric gravity wave—known as a mesospheric bore—makes the density of oxygen in the atmosphere fluctuate.

"When there is then electron precipitation to a more denser part of the wave, that gives more auroral emission and light in comparison to the adjacent place where the oxygen density is more tenuous," Palmroth told Newsweek. "So the aurora acts to illuminate the wave."

A book that Palmroth published in 2018 was key to the identification of the new auroral form. The book contained numerous photographs of different kinds of aurorae snapped by amateur astronomers. But it became apparent that one of the forms contained in the book could not be easily categorized.

By chance, the unidentified auroral form appeared again just days after the book was published and photographers immediately notified Palmroth who started to investigate.

"One of the most memorable moments of our research collaboration was when the phenomenon appeared at that specific time and we were able to examine it in real-time," amateur astronomer Matti Helin said in a statement.

Following this sighting, hobbyists rushed to find out more about the unidentified phenomenon to understand what was happening.

aurora, Finland
The newly identified auroral form. Kari Saari

"It was like piecing together a puzzle or conducting detective work," Helin said. "Every day we found new images and came up with new ideas. Eventually, we got to the bottom of it."

Images were snapped of the unidentified aurora form in two locations in southwestern Finland, both of which displayed common characteristics. Furthermore, Palmroth and her colleagues used astronomical software to work out the altitude and extent of the phenomenon.

In addition, a service known as "Sky Watch" maintained by the Finnish Amateur Astronomer Association spotted a further seven events that displayed the distinctive wave pattern.

The "dunes" were observed in a part of the Earth's atmosphere—on the boundary between what is normally considered "space"—that is not well understood.

"Due to the difficulties in measuring the atmospheric phenomena occurring between 80 and 120 kilometers [50 to 75 miles] in altitude, we sometimes call this area 'the ignorosphere,'" Palmroth said.

In 2018, scientists announced the discovery of an entirely new celestial phenomenon which some had previously thought was a form of aurora. Known as STEVE, the phenomenon consists of spectacular glowing ribbons of purple and white light which sometimes appear in the night sky.

Amateur skywatchers had snapped pictures of these ribbons for decades before scientists were finally able to formally identify them.