The space environment that surrounds our planet is fascinating and incredibly mysterious. Charged particles coming from the Sun and the rest of the universe slam into our magnetic field, creating many different effects. Among this, there lies the open question of how electrons are accelerated by the magnetosphere to almost the speed of light.

Researchers using NASA’s THEMIS (Time History of Events and Macroscale Interactions during Substorms) satellites have discovered that cosmic electrons are accelerated by electromagnetic interactions in the foreshock, a region just beyond Earth’s magnetic field.

This discovery, published in Physical Review Letters, provides the first clue towards an understanding of these high-energy electrons. Before THEMIS’ observations, these electrons were thought to be accelerated much closer to our planet, so scientists were trying to work out what’s going on.  

“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, co-author and THEMIS project scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, in a statement.

“There is a gap in our knowledge, something basic is missing.”

This missing knowledge is crucial not only for planetary physics but also for many other disciplines. These high-energy electrons have been observed around other planets too, and they might affect satellites and equipment. The high-speed particles might become dangerous as we step beyond the safe bubble of our planet and into deep space.

“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,” said Lynn Wilson, lead author of the paper from NASA Goddard.

There has been 50 decades worth of observations of high-energy particles within the foreshock region, although the observations were not quick enough to discover that they originated from the region itself. Researchers will continue to monitor the foreshock with THEMIS and, hopefully, they will find out what’s the cause behind the electrons' impressive speeds.