UMN study solves decades-old space mystery

The research put to end 50 years of speculation and confirmed that chorus waves cause electron microbursts.

Helen Sabrowsky

A new study from University of Minnesota experts solves a 50-year-old space mystery and shows that relatively inexpensive satellites are viable options for astrophysics research.

The study is the first to confirm the long-held belief that mysterious sounds in space produced by certain waves are one of the causes of electron microbursts. Researchers used inexpensive, partially student-built satellites to collect data, and now, some scientists hope to use this type of satellite for other space research.

Scientists set out to quantify electron loss from the radiation belt, which in the past could only be done using Van Allen probes that cost several hundred million dollars, said Aaron Breneman, University research scientist and the study’s lead author. 

For this study, accepted for publication this month, scientists used CubeSats — miniaturized satellites about the size of a loaf of bread — from NASA’s FIREBIRD II Mission along with the Van Allen probe. These satellites are better-suited for this research and much less expensive, Breneman said.

The Van Allen Probes orbit in the chorus source region, while the FIREBIRD II CubeSat orbit is much closer —  about 500 km from Earth, said Harlan Spence, director of the University of New Hampshire’s Institute for the Study of Earth, Oceans and Space. 

When the orbits of the CubeSat and Van Allen probe reach the same magnetic field, called a conjunction, scientists can study electron loss at both points, he said.

The FIREBIRD II satellites were critical to the research because the Van Allen’s probe is typically unable to differentiate between electrons trapped in space and electrons that are about to be lost to the atmosphere, which is closer to Earth, Breneman said. 

Plus, the Van Allen probes have a limited view of electron loss because they are so far away from Earth, while the FIREBIRD CubeSats are actually hit by the particles scientists want to measure, said John Sample, physics professor at Montana State University. 

“It’s a way of doing a cause and effect comparison that you can’t do with a single satellite,” Breneman said.

This is the first published research that “affirmed the mechanism of how electromagnetic waves scatter these electrons, which cause them to rain down into the atmosphere,” Spence said.

The research put to end 50 years of speculation and confirmed the long-held belief that chorus waves — which make ringing sounds in space — cause these electron microbursts, Sample said.

This type of research has been difficult to conduct in the past because scientists didn’t have the right satellites to collect data. 

“Theoretically speaking, it makes sense, but it’s so hard to make conjunctions because you have to have the right observing platforms,” Breneman said.

The FIREBIRD II Mission’s CubeSats made the research possible, Breneman said. They also proved inexpensive, student-built spacecraft can be useful as a complement to more sophisticated satellites, like the Van Allen probes, Spence said. 

Additionally, the FIREBIRD II CubeSats performed better than scientists expected them to initially, Sample said. Since the findings were released, there has been increased pressure from the scientific community to build and launch more, he said. 

“The complementary nature of these has been very surprising and has led to very large scientific payoffs,” Breneman said. “It also trains students and gets them deeply involved in missions that actually return science. These are missions that everyone in our field is interested in.”