Red and green auroras may share electron-driven origins

With their mysterious glow and swirling veils of color, auroras enchant even experienced researchers. When a particularly intense solar storm reached Earth on the night of May 10, 2024, and relevant websites predicted auroras even for southern Lower Saxony, several researchers from the Technical University of Braunschweig, the Fraunhofer Institute for Surface Engineering and Thin Films IST, the University of Göttingen, and the Max Planck Institute for Solar System Research (MPS) took to the outdoors.

“I’ve seen many auroras at higher latitudes. Above Göttingen, they’re a rarity. I absolutely wanted to photograph them. I wasn’t originally interested in using the photos for scientific purposes,” MPS director and passionate photographer Sami K. Solanki recalls his nighttime excursion.

Philipp Schulz from the Fraunhofer Institute for Surface Engineering and Thin Films IST, Ingo von Borstel from the Institute for Geophysics and Extraterrestrial Physics at the Technical University of Braunschweig, and Klaus Reinsch from the Institute for Astrophysics and Geophysics at the University of Göttingen shared the same experience as the Göttingen-based solar researcher. Yet their images proved to be as picturesque as they were unusual: Above the green auroras near the surface, a reddish glow can be seen; bright rays extend downward from red to green.

“Rays continuously connecting the red aurora above to the green aurora below have not been reported in any scientific paper,” says Bruce T. Tsurutani, a former scientist at NASA’s Jet Propulsion Laboratory (JPL) and first author of the new study published in Annales Geophysicae. “They have helped us understand the origin of the red glow,” he adds. Yasuhito Narita of the Technical University of Braunschweig coordinated the international team of researchers, who compared the images with data on the solar wind and disturbances in the Earth’s magnetic field.

Search for energy sources

The May 10, 2024, storm was the second most intense magnetic storm of the space age (since 1958). Red auroras occur during intense magnetic storms at middle latitudes, typically at altitudes ranging from 800 to 200 kilometers (497 to 124 miles). The mechanism behind red auroral formation has been the subject of extensive theoretical research. Many different ideas have been proposed. But because there typically are no satellites going through red aurora space, these theories have not been tested.

Green auroras occur during typical nights in the polar regions. Fast electrons from the Earth’s magnetosphere race along the lines of Earth’s magnetic field—almost like on a slide—and advance within the atmosphere to an altitude of 130 to 85 kilometers (81 to 53 miles) above Earth’s surface. There, they set off a cascade of collisions that ultimately cause oxygen atoms to glow green.

The photographs taken on May 10, 2024, now point to a resolution of the many theories of red auroras. “The fact that the bright rays extend from the red to the green aurora suggests that the same physical process is at work in both cases,” explains Narita. The current analyses show that red auroras, just like green ones, can be caused by electrons streaming down from the sun.

Citizen science

Following an 11-year cycle, the sun goes through calmer and more active phases. At the peak of its activity, our star displays intense solar flares and hurls particularly fast solar wind plasmas and embedded magnetic fields into space in massive eruptions. When these magnetic fields strike Earth’s magnetosphere, magnetic reconnection occurs, transferring solar wind energy to the Earth’s magnetosphere, leading to a chain of events that cause auroras, sometimes even at midlatitudes.

Since 2024, auroras have been visible several more times over southern Lower Saxony. Currently, solar activity is declining again. However, even during this phase, unusually intense eruptions can still occur.

“Anyone who takes photos of the aurora with a smartphone or camera can contribute to their study,” said Narita.

Researchers at the Technical University of Braunschweig are therefore counting on the public’s help and asking people to share photographs of future aurorae with them. To achieve scientifically meaningful pictures, it is important to use a relatively short exposure time of no more than six seconds. This is the only way to capture the telltale rays.

Who’s behind this story?

Lisa Lock

BA art history, MA material culture. Former museum editor, paramedic, and transplant coordinator. Editing for Science X since 2021.

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Robert Egan

Bachelor’s in mathematical biology, Master’s in creative writing. Well-traveled with unique perspectives on science and language.

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