New insight into Earth's magnetic field

New insight into Earth's magnetic field

NASA's new observations of the Earth's magnetic field indicate that its foreshock region is capable of accelerating electrons to almost the speed of light. 

Earth's magnetic field deflects the incoming charged particles from the Sun. In regions outside the magnetic field, the particles are disturbed and reflected into the so-called foreshock region, a highly turbulent area. 

Newly collected data from the 'Time History of Events and Macroscale Interactions during Substorms' (THEMIS) mission suggest the foreshock region can accelerate some particles to speeds approaching the speed of light. Particles of such speeds have been observed in space near our planet, as well as in other parts of the universe. However, it has still not been explained how they obtain such extreme speeds.

The data was collected by the five THEMIS satellites, deployed with the purpose of studying Earth's magnetosphere and how it captures and releases solar wind. The orbit of the satellites passed through the foreshock regions. 

According to the new research, electrons can obtain high speed in the near-Earth region at larger distances from our planet than previously thought. The discovery has raised questions about the cause of such acceleration, and it indicates the particles can be accelerated not only in the near-Earth field but throughout the 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 study at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

Video credit: NASA Goddard's Scientific Visualization Studio/Tom Bridgman, data visualizer

The new study explains how the particles can get the acceleration in certain areas just beyond the magnetic field of our planet. The region named bow shock, a protective shield from the solar wind is the first region encountered by the coming particles. It slows them down and deflects most of them away. Those particles that get reflected back toward the Sun, form the so-called foreshock region.

Some particles in this region are fast and high-energy electrons or ions which, according to new research, can gain energy through the electromagnetic activity in the foreshock area.

The spacecraft have discovered electrons of extremely high energy. The observations of their acceleration were less than a minute long. However, the observed energies were much higher than an average energy level of particles in this region, and well beyond levels managed by collisions only. Observations conducted from the Heliophysics spacecraft, Wind, and STEREO, at the same time did not detect any solar radio bursts or interplanetary shocks which would relate the observed electrons to the solar activity.

“This is a puzzling case because we’re seeing energetic electrons where we don’t think they should be, and no model fits them. There is a gap in our knowledge, something basic is missing,” said David Sibeck, co-author and THEMIS project scientist at NASA Goddard.

The scientists also confirmed the electrons did not come from the bow shock but their accelerations were found to originate from within the foreshock region.

The particles of high energy have been observed in the foreshock region throughout the last 50 years. However, it is only now that was discovered they originate from within the area. The observations conducted so far have been averaged over several minutes while new ones, from THEMIS, have been gathered at a much faster pace, enabling the discovery.

Further research is expected to clarify how the electrons obtain such high acceleration.

Featured image credit: NASA Goddard's Scientific Visualization Studio/Tom Bridgman, data visualizer


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