[ RadSafe ] UCLA astronomers solve mystery of vanishing electrons
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Mon Jan 30 00:19:18 CST 2012
UCLA astronomers solve mystery of vanishing electrons
Findings further efforts to better predict geomagnetic storms in space
By Kim DeRose January 29, 2012 Category: Research
UCLA's Drew Turner
UCLA researchers have explained the puzzling disappearing act of energetic
electrons in Earth's outer radiation belt, using data collected from a fleet of
In a paper published Jan. 29 in the advance online edition of the journal Nature
Physics, the team shows that the missing electrons are swept away from the
planet by a tide of solar wind particles during periods of heightened solar
"This is an important milestone in understanding Earth's space environment,"
said lead study author Drew Turner, an assistant researcher in the UCLA
Department of Earth and Space Sciences and a member of UCLA's Institute for
Geophysics and Planetary Physics (IGPP). "We are one step closer towards
understanding and predicting space weather phenomena."
During powerful solar events such as coronal mass ejections, parts of the
magnetized outer layers of sun's atmosphere crash onto Earth's magnetic field,
triggering geomagnetic storms capable of damaging the electronics of orbiting
spacecraft. These cosmic squalls have a peculiar effect on Earth's outer
radiation belt, a doughnut-shaped region of space filled with electrons so
energetic that they move at nearly the speed of light.
"During the onset of a geomagnetic storm, nearly all the electrons trapped
within the radiation belt vanish, only to come back with a vengeance a few hours
later," said Vassilis Angelopoulos, a UCLA professor of Earth and space sciences
and IGPP researcher.
The missing electrons surprised scientists when the trend was first measured in
the 1960s by instruments onboard the earliest spacecraft sent into orbit, said
study co-author Yuri Shprits, a research geophysicist with the IGPP and the
departments of Earth and space sciences, and atmospheric and oceanic sciences.
"It's a puzzling effect," he said. "Oceans on Earth do not suddenly lose most of
their water, yet radiation belts filled with electrons can be rapidly
Even stranger, the electrons go missing during the peak of a geomagnetic storm,
a time when one might expect the radiation belt to be filled with energetic
particles because of the extreme bombardment by the solar wind.
Where do the electrons go? This question has remained unresolved since the early
1960s. Some believed the electrons were lost to Earth's atmosphere, while others
hypothesized that the electrons were not permanently lost at all but merely
temporarily drained of energy so that they appeared absent.
"Our study in 2006 suggested that electrons may be, in fact, lost to the
interplanetary medium and decelerated by moving outwards," Shprits said.
"However, until recently, there was no definitive proof for this theory."
To resolve the mystery, Turner and his team used data from three networks of
orbiting spacecraft positioned at different distances from Earth to catch the
escaping electrons in the act. The data show that while a small amount of the
missing energetic electrons did fall into the atmosphere, the vast majority were
pushed away from the planet, stripped away from the radiation belt by the
onslaught of solar wind particles during the heightened solar activity that
generated the magnetic storm itself.
A greater understanding of Earth's radiation belts is vital for protecting the
satellites we rely on for global positioning, communications and weather
monitoring, Turner said. Earth's outer radiation belt is a harsh radiation
environment for spacecraft and astronauts; the high-energy electrons can
penetrate a spacecraft's shielding and wreak havoc on its delicate electronics.
Geomagnetic storms triggered when the oncoming particles smash into Earth's
magnetosphere can cause partial or total spacecraft failure.
"While most satellites are designed with some level of radiation protection in
mind, spacecraft engineers must rely on approximations and statistics because
they lack the data needed to model and predict the behavior of high-energy
electrons in the outer radiation belt," Turner said.
During the 2003 "Halloween Storm," more than 30 satellites reported
malfunctions, and one was a total loss, said Angelopoulos, a co-author of the
current research. As the solar maximum approaches in 2013, marking the sun's
peak activity over a roughly 11-year cycle, geomagnetic storms may occur as
often as several times per month.
"High-energy electrons can cut down the lifetime of a spacecraft significantly,"
Turner said. "Satellites that spend a prolonged period within the active
radiation belt might stop functioning years early."
While a mechanized spacecraft might include multiple redundant circuits to
reduce the risk of total failure during a solar event, human explorers in orbit
do not have the same luxury. High-energy electrons can punch through astronauts'
spacesuits and pose serious health risks, Turner said.
"As a society, we've become incredibly dependent on space-based technology," he
said. "Understanding this population of energetic electrons and their extreme
variations will help create more accurate models to predict the effect of
geomagnetic storms on the radiation belts."
Key observational data used in this study was collected by a network of NASA
spacecraft known as THEMIS (Time History of Events and Macroscale Interactions
during Substorms); Angelopoulos is the principal investigator of the THEMIS
mission. Additional information was obtained from two groups of weather
satellites called POES (Polar Operational Environmental Satellite) and GOES
(Geostationary Operational Environmental Satellite).
A new collaboration between UCLA and Russia's Moscow State University promises
to paint an even clearer picture of these vanishing electrons. Slated for launch
in the spring of 2012, the Lomonosov spacecraft will fly in low Earth orbit to
measure highly energetic particles with unprecedented accuracy, said Shprits,
the principal investigator of the project. Several key instruments for the
mission are being developed and assembled at UCLA.
Earth's radiation belts were discovered in 1958 by Explorer I, the first U.S.
satellite that traveled to space.
"What we are studying was the first discovery of the space age," Shprits said.
"People realized that launches of spacecraft didn't only make the news, they
could also make scientific discoveries that were completely unexpected."
This project received federal funding from NASA and the National Science
Foundation. Other co-authors include Michael Hartinger, a UCLA graduate student
in Earth and space sciences.
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