A critical component of auroral formation is much higher in space than previously thought, according to a new study. Aurora requires electrical acceleration to propel charged particles down through the atmosphere. Scientists have found that acceleration exists beyond 30,000 kilometers above the surface of the Earth, and this is changing the idea not only of the Earth, but also of other planets.
The aurora borealis begins their formation from supersonic plasma, which the Sun launches into space in the form of high-speed charged particles – protons. As they approach the Earth, they deflect and flow along the lines of force of the planet’s magnetic field, eventually rushing towards the magnetic poles.
“Most of the electrons in the magnetosphere do not reach the part of the upper atmosphere called the ionosphere because they are repelled by the Earth’s magnetic field. We do not know all the details of how the electric field is generated that accelerates the electrons into the ionosphere, or even how high it is above the Earth.”Shun Imajo of Earth and Space Environmental Research Institute, Nagoya University
But some particles get a burst of energy by accelerating in the Earth’s upper atmosphere, where they collide and excite oxygen and nitrogen atoms at an altitude of about 100 kilometers. When these atoms come out of their state of excitement, they radiate a radiance. However, many details of this process remain a mystery.
Scientists have suggested that the acceleration of electrons occurs at an altitude of 1000 to 20,000 kilometers above the Earth. But new research has shown that the area of acceleration extends beyond 30,000 kilometers.
The electric field accelerating auroral particles can exist at any height along the magnetic field line and is not limited to the transition region between the ionosphere and magnetosphere at a distance of several thousand kilometers. This suggests that currently unknown magnetospheric mechanisms are at work here.
The team came to this conclusion by studying data from an electron detector on the Japanese satellite Arase, which studies the radiation belt in the Earth’s inner magnetosphere. The data was obtained when the satellite was at an altitude of about 30,000 kilometers and for several minutes was inside a thin active auroral arc. The team was able to measure the upward and downward motions of the electrons, ultimately finding that the region of acceleration of the electrons begins above the satellite and extends below it.
To further explore this so-called very large acceleration region, the team intends to analyze data from several auroral phenomena, compare observations at high and low altitudes, and perform numerical simulations of the electric potential.
Understanding how this electric field is formed will fill in the gaps in knowledge about how auroral radiation appears and electrons and protons are transported on Earth and other planets, including Jupiter and Saturn.