[ RadSafe ] UCLA astronomers solve mystery of vanishing electrons

[ROY HERREN]

http://newsroom.ucla.edu/portal/ucla/ucla-researchers-solve-mystery-221811.aspx
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 
orbiting spacecraft.

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 
activity.

"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 
depopulated."

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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