NASA discovers mysterious super-fast electrons whizzing above Earth

Understanding the source could aid space missions

Electrons are being whipped to speeds close to the speed of light just outside the Earth’s magnetic field, and scientists aren’t sure why.

NASA’s Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission has discovered these extremely fast particles farther from Earth than previously thought possible.

The Sun flings supersonic electrons out to space, and some fly towards Earth but are deflected away by Earth’s magnetic field.

The series of the magnetic fields covers the Earth and creates a protective bubble known as the magnetosphere. As the magnetosphere moves through space, a bow shock ripples through space as the electrons are slowed and deflected away.

Some electrons end up being reflected towards the Sun, and end up in a pool surrounding the bow shock in the foreshock region.

A paper published in Physical Review Letters [paywalled] shows that some electrons in the foreshock are being excited to relativistic speeds.

Photo credit: NASA/SGFC

Scientists have always believed that electrons reach such fast speeds because they are bounced back and forth across the bow shock, gaining speed with each collision.

But, after analyzing data taken from NASA’s THEMIS spacecraft, a team of scientists led by NASA’s Goddard Space Flight Center have found that the average energy of the electrons does not match the energies given from the collisions alone.

Observations made by NASA’s Heliophysics, Wind, and STEREO spacecrafts revealed no solar radio bursts or interplanetary shocks that could have imparted extra energy to the electrons. The high speeds cannot be explained with any solar activity and do not originate from the bow shock area, leaving scientists perplexed.

“This is a puzzling case because we’re seeing energetic electrons where we don’t think they should be, and no model fits them,” said David Sibeck, coauthor of the paper and a project scientist working on the THEMIS mission. “There is a gap in our knowledge – something basic is missing.”

Although high-energy electrons have been observed in the foreshock region for more than 50 years, it wasn’t known that they sprang from the foreshock region itself. It could be because the electrons are accelerated over a short burst of time, and most spacecrafts can only detect changes over minutes.

Solving the mechanism that produces these relativistic electrons is important, said Lynn Wilson, lead author of the paper and researcher at NASA’s Goddard Space Flight Center.

“This affects pretty much every field that deals with high-energy particles, from studies of cosmic rays to solar flares and coronal mass ejections, which have the potential to damage satellites and affect astronauts on expeditions to Mars.”

Relativistic electrons can cause equipment to fail and even penetrate through space suits, giving astronauts a strong dose of radiation capable of damaging DNA. ®

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