UCLA researchers have identified a new source of super-fast, powerful electrons showering down on Earth, a phenomena that contributes to the brilliant aurora borealis but also presents a threat to satellites, spacecraft, and astronauts.
The researchers used the ELFIN mission, a pair of miniature satellites constructed and managed on the UCLA campus by undergraduate and graduate students directed by a small team of professional mentors, to witness unexpected, fast “electron precipitation” from low-Earth orbit.
The scientists determined that the sudden downpour was caused by whistler waves, a type of electromagnetic wave that ripples through plasma in space and affects electrons in the Earth’s magnetosphere, causing them to “spill over” into the atmosphere by combining the ELFIN data with more distant observations from NASA’s THEMIS spacecraft.
Their results, which were published on March 25 in the journal Nature Communications, show that whistler waves cause significantly more electron rain than current theories and space weather models indicate.
“ELFIN is the first satellite to detect these super-fast electrons,” said Xiaojia Zhang, principal author and professor of Earth, planetary, and space sciences at UCLA. “Due to its unique vantage position in the sequence of events that creates them, the mission is giving fresh insights.”
The near-Earth space environment, which is loaded with charged particles circling in vast rings around the globe known as Van Allen radiation belts, is important to that sequence of events. Electrons in these belts bounce between the Earth’s north and south poles in Slinky-like spirals. Whistler waves are formed inside the radiation belts under particular circumstances, energizing and speeding up the electrons. This essentially lengthens the electrons’ journey route to the point where they fall out of the belts and precipitate into the atmosphere, resulting in electron rain.
According to Vassilis Angelopolous, a UCLA professor of space physics and ELFIN’s primary scientist, one may consider the Van Allen belts as a vast reservoir filled with water – or, in this example, electrons. Water regularly spirals down into a relief drain as the reservoir fills, preventing the basin from overflowing. When huge waves form in the reservoir, however, the sloshing water goes over the edge quicker and in greater volume than the relief drainage. ELFIN, which is downstream of both rivers, can accurately estimate their contributions.
The ELFIN measurements of low-altitude electron rain, along with THEMIS observations of whistler waves in space and extensive computer modeling, enabled the team to grasp in detail how the waves generate fast torrents of electrons to pour into the atmosphere.
Current theories and space weather models, although accounting for other sources of electrons entering the atmosphere, do not foresee this additional whistler wave-induced electron flow, which may influence Earth’s atmospheric chemistry, pose dangers to spacecraft, and harm low-orbiting satellites.
The researchers also demonstrated that during geomagnetic storms, which are produced by increased solar activity and may alter near-Earth space and the Earth’s magnetic environment, this sort of radiation-belt electron loss to the atmosphere can rise dramatically.
“Although space is often regarded to be distinct from our upper atmosphere, the two are intricately connected,” Angelopoulos said. “Knowing how they’re connected might help satellites and astronauts travelling through the area, which is becoming more essential for business, telecommunications, and space tourism.”
ELFIN (Electron Losses and Fields Investigation), which is financed by NASA and the National Science Foundation, has employed over 300 UCLA students since its launch in 2013. The two microsatellites, which are around the size of a loaf of bread and weigh about 8 pounds each, were put into orbit in 2018 and have since been tracking the activities of energetic electrons and assisting scientists in better understanding the influence of magnetic storms in near-Earth space. The satellites are managed by the UCLA Mission Operations Center, which is located on campus.