Wednesday,
December 3, 2014
Shield of Invisibility Mysteriously Cloaked Around Planet Earth
Team led by the University of Colorado Boulder has discovered an
invisible shield some 7,200 miles above Earth that blocks so-called
"killer electrons," which whip around the planet at near-light speed
and have been known to threaten astronauts, fry satellites and degrade space
systems during intense solar storms.
The barrier to the particle motion was discovered in the Van Allen
radiation belts, two doughnut-shaped rings above Earth that are filled with
high-energy electrons and protons, said Distinguished Professor Daniel Baker,
director of CU-Boulder's Laboratory for Atmospheric and Space Physics (LASP).
Held in place by Earth's magnetic field, the Van Allen radiation belts
periodically swell and shrink in response to incoming energy disturbances from
the sun.
As the first significant discovery of the space age, the Van Allen
radiation belts were detected in 1958 by Professor James Van Allen and his team
at the University of Iowa and were found to be composed of an inner and outer
belt extending up to 25,000 miles above Earth's surface. In 2013, Baker -- who
received his doctorate under Van Allen -- led a team that used the twin Van
Allen Probes launched by NASA in 2012 to discover a third, transient
"storage ring" between the inner and outer Van Allen radiation belts
that seems to come and go with the intensity of space weather.
The latest mystery revolves around an "extremely sharp"
boundary at the inner edge of the outer belt at roughly 7,200 miles in altitude
that appears to block the ultrafast electrons from breeching the shield and
moving deeper towards Earth's atmosphere.
"It's almost like theses electrons are running into a glass
wall in space," said Baker, the study's lead author. "Somewhat like
the shields created by force fields on Star Trek that were used to repel alien
weapons, we are seeing an invisible shield blocking these electrons. It's an
extremely puzzling phenomenon."
A paper on the subject was published in the Nov. 27 issue of Nature.
The team originally thought the highly charged electrons, which
are looping around Earth at more than 100,000 miles per second, would slowly
drift downward into the upper atmosphere and gradually be wiped out by
interactions with air molecules. But the impenetrable barrier seen by the twin
Van Allen belt spacecraft stops the electrons before they get that far, said Baker.
The group looked at a number of scenarios that could create and
maintain such a barrier. The team wondered if it might have to do with Earth's
magnetic field lines, which trap and control protons and electrons, bouncing
them between Earth's poles like beads on a string. The also looked at whether
radio signals from human transmitters on Earth could be scattering the charged
electrons at the barrier, preventing their downward motion. Neither explanation
held scientific water, Baker said.
"Nature abhors strong gradients and generally finds ways to
smooth them out, so we would expect some of the relativistic electrons to move
inward and some outward," said Baker. "It's not obvious how the slow,
gradual processes that should be involved in motion of these particles can
conspire to create such a sharp, persistent boundary at this location in
space."
Another scenario is that the giant cloud of cold, electrically
charged gas called the plasmasphere, which begins about 600 miles above Earth
and stretches thousands of miles into the outer Van Allen belt, is scattering
the electrons at the boundary with low frequency, electromagnetic waves that
create a plasmapheric "hiss," said Baker. The hiss sounds like white
noise when played over a speaker, he said.
While Baker said plasmaspheric hiss may play a role in the
puzzling space barrier, he believes there is more to the story. "I think
the key here is to keep observing the region in exquisite detail, which we can
do because of the powerful instruments on the Van Allen probes. If the sun
really blasts Earth's magnetosphere with a coronal mass ejection (CME), I
suspect it will breach the shield for a period of time," said Baker, also
a faculty member in the astrophysical and planetary sciences department.
"It's like looking at the phenomenon with new eyes, with a
new set of instrumentation, which give us the detail to say, 'Yes, there is
this hard, fast boundary,'" said John Foster, associate director of MIT's
Haystack Observatory and a study co-author.
Source:
University of Colorado at Boulder via sciencedaily.com
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