'Star Trek' shield above Earth blocks killer electrons

Scientists have discovered an invisible Star Trek-style shield nearly 11,600 km above Earth that blocks the so-called 'killer electrons', which have been known to threaten astronauts and fry satellites 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 University of Colorado Boulder's Laboratory for Atmospheric and Space Physics (LASP).
The Van Allen radiation belts detected in 1958 are composed of an inner and outer belt extending up to 40,233 km above Earth's surface.

In 2013, Baker 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 11,587 km in altitude that appears to block the ultrafast electrons from breeching the shield and moving deeper towards Earth's atmosphere.
"It's almost like these 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," Baker said.

The team originally thought the highly charged electrons, which are looping around Earth at more than 160,934 km 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 team wondered if the Earth's magnetic field lines, which trap and control protons and electrons, bouncing them between Earth's poles like beads on a string, might have something to do with creating and maintaining such a barrier.

They 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," Baker said.
The study was published in the journal Nature.