Electron rain? Researchers reveal the source of a mysterious space phenomenon

The phenomenon could be hazardous to astronauts and space equipment.
Chris Young
An artist's impression of one of the ELFIN satellites.Emmanuel Masongsong/UCLA

Scientists used a NASA-funded CubeSat to reveal a phenomenon that sees super-fast energetic electrons rain down over Earth, a press statement reveals.

The electron rain contributes to the stunning aurora borealis, but could also put satellites, spacecraft, and even astronauts in danger.

Scientists from the University of California Los Angeles (UCLA) observed the rain, called "electron precipitation," from low-Earth orbit during the Electron Losses and Fields Investigation, or ELFIN, mission. The ELFIN team launched a pair of small satellites into orbit aboard a NASA Delta II launch vehicle on September 15, 2018 to analyze the atmospheric phenomenon. 

The researchers used advanced computer modeling, combining their data with information from a previous NASA observation, to determine that the electron rain was caused by whistler waves, a type of electromagnetic wave that moves through plasma. They laid out their findings in a paper published in Nature Communications, which also outlined the fact that they found more electron rain than leading theories predicted.

Electron rain? Researchers reveal the source of a mysterious space phenomenon
Electrons in a Van Allen radiation belt (blue) are triggered by whistler waves (purple) to rain down (red) toward the north pole. Source: Zhang, et al./Nature Communications, 2022

"ELFIN is the first satellite to measure these super-fast electrons," said Xiaojia Zhang of UCLA, lead author on the new paper. "The mission is yielding new insights due to its unique vantage point."

"At the cutting edge of space weather studies"

The satellite is focused on the Van Allen radiation belts that surround Earth and are composed of highly energetic charged particles, most of which originate from the solar wind. Later this year, we should gain a better understanding of how this radiation can affect humans, thanks to the SpaceX Polaris Dawn mission, which will conduct the highest-ever spacewalk above the line of the radiation belt.

The new research provides insight into the way electronic vibrations called whistler waves can occur in the radiation belts, which energize and speed up the electrons so much that they rain down into the atmosphere. It does so at a much higher rate than previous estimates suggested.

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"Data from the ELFIN satellites are at the cutting edge of space weather studies and will be heavily used by researchers around the world over the next decade," said Ethan Tsai, a co-author and project manager at UCLA. "So we’ve worked very hard to make our data open and easily accessible to the entire space science community."

The researchers say that studying this phenomenon is important for terrestrial modeling, as well as for understanding Earth's magnetic environment. Most importantly, it will also help to gauge possible dangers to astronauts and space machinery from the highly charged space precipitation.