UCLA scientists have discovered a new source of super-fast, energetic
electrons raining down on Earth, a phenomenon that contributes to the
colorful aurora borealis but also poses hazards to satellites, spacecraft
and astronauts.
The researchers observed unexpected, rapid “electron precipitation” from
low-Earth orbit using the ELFIN mission, a pair of tiny satellites built and
operated on the UCLA campus by undergraduate and graduate students guided by
a small team of staff mentors.
By combining the ELFIN data with more distant observations from NASA’s
THEMIS spacecraft, 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.
Their findings, published March 25 in the journal Nature Communications,
demonstrate that whistler waves are responsible for far more electron rain
than current theories and space weather models predict.
“ELFIN is the first satellite to measure these super-fast electrons,” said
Xiaojia Zhang, lead author and a researcher in UCLA’s department of Earth,
planetary and space sciences. “The mission is yielding new insights due to
its unique vantage point in the chain of events that produces them.”
Central to that chain of events is the near-Earth space environment, which
is filled with charged particles orbiting in giant rings around the planet,
called Van Allen radiation belts. Electrons in these belts travel in
Slinky-like spirals that literally bounce between the Earth’s north and
south poles. Under certain conditions, whistler waves are generated within
the radiation belts, energizing and speeding up the electrons. This
effectively stretches out the electrons’ travel path so much that they fall
out of the belts and precipitate into the atmosphere, creating the electron
rain.
One can imagine the Van Allen belts as a large reservoir filled with water —
or, in this case, electrons, said Vassilis Angelopolous, a UCLA professor of
space physics and ELFIN’s principal investigator. As the reservoir fills,
water periodically spirals down into a relief drain to keep the basin from
overflowing. But when large waves occur in the reservoir, the sloshing water
spills over the edge, faster and in greater volume than the relief drainage.
ELFIN, which is downstream of both flows, is able to properly measure the
contributions from each.
The low-altitude electron rain measurements by ELFIN, combined with the
THEMIS observations of whistler waves in space and sophisticated computer
modeling, allowed the team to understand in detail the process by which the
waves cause rapid torrents of electrons to flow into the atmosphere.
The findings are particularly important because current theories and space
weather models, while accounting for other sources of electrons entering the
atmosphere, do not predict this extra whistler wave–induced electron flow,
which can affect Earth’s atmospheric chemistry, pose risks to spacecraft and
damage low-orbiting satellites.
The researchers further showed that this type of radiation-belt electron
loss to the atmosphere can increase significantly during geomagnetic storms,
disturbances caused by enhanced solar activity that can affect near-Earth
space and Earth’s magnetic environment.
“Although space is commonly thought to be separate from our upper
atmosphere, the two are inextricably linked,” Angelopoulos said.
“Understanding how they’re linked can benefit satellites and astronauts
passing through the region, which are increasingly important for commerce,
telecommunications and space tourism.”
Since its inception in 2013, more than 300 UCLA students have worked on
ELFIN (Electron Losses and Fields investigation), which is funded by NASA
and the National Science Foundation. The two microsatellites, each about the
size of a loaf of bread and weighing roughly 8 pounds, were launched into
orbit in 2018, and since then have been observing the activity of energetic
electrons and helping scientists to better understand the effect of magnetic
storms in near-Earth space. The satellites are operated from the UCLA
Mission Operations Center on campus.
“It’s so rewarding to have increased our knowledge of space science using
data from the hardware we built ourselves,” said Colin Wilkins, a co-author
of the current research who is the instrument lead on ELFIN and a space
physics doctoral student in the department of Earth, planetary and space
sciences.
Reference:
Zhang, XJ., Artemyev, A., Angelopoulos, V. et al. Superfast precipitation of
energetic electrons in the radiation belts of the Earth. Nat Commun 13, 1611
(2022).
DOI: 10.1038/s41467-022-29291-8
Tags:
Space & Astrophysics