Earth's Inner Radiation Belt May Be Much Weaker Than Previously Thought

radiation_belts_0 — An artist's depiction with cutaway section of the two giant donuts of radiation, called the Van Allen Belts, that surround Earth. NASA/Goddard Space Flight Center/Scientific Visualization Studio

Earth (and other magnetized planets within and beyond the solar system) is surrounded by two donut-shaped regions of charged particles. These Van Allen belts, held in place by Earth’s magnetic field, are regions of high turbulence, shrinking and swelling in response to solar winds and flares.

Scientists have long thought that unlike the outer radiation belt, the inner one, which stretches between 400 and 6,000 miles above Earth’s surface, is more or less sedate, and that its composition remains largely constant. However, a new study published in the Journal of Geophysical Research has now disabused them of this notion.

Read: No Cause For Alarm Over Earth’s Magnetic Field

The study, based on observations made using NASA’s Van Allen Probes, reveals that the inner radiation belts very rarely contain superfast — or relativistic — electrons. Although these high-energy particles can be pushed deep into the inner belt by strong geomagnetic storms (such as the one seen in June 2015), in the normal course of events, the inner belt is composed of high-energy protons and low-energy electrons.

“Given the rarity of the storms, which can inject relativistic electrons into the inner belt, the scientists now understand there to typically be lower levels of radiation there — a result that has implications for spacecraft flying in the region,” NASA said in a statement released Wednesday. “Knowing exactly how much radiation is present may enable scientists and engineers to design lighter and cheaper satellites tailored to withstand the less intense radiation levels they’ll encounter.”

inner_electron_belt_illustration — During a strong geomagnetic storm, electrons at relativistic energies, which are usually only found in the outer radiation belt, are pushed in close to Earth and populate the inner belt. While the electrons in the slot region quickly decay, the inner belt electrons can remain for many months. NASA’s Goddard Space Flight Center/Mary Pat Hrybyk-Keith

The discovery was made using the Van Allen Probes’ magnetic electron and ion spectrometer, which allowed researchers to distinguish high-energy electrons from high-energy protons. By separating the two classes of particles, scientists were able to get a clearer picture of what the population of particles in the inner belt looks like.

“When we carefully process the data and remove the contamination, we can see things that we’ve never been able to see before,” study lead author Seth Claudepierre, a Van Allen Probes scientist at the Aerospace Corporation in California, said in the statement. “These results are totally changing the way we think about the radiation belt at these energies.”