Van Allen Probes: 'Zebra stripe' structure in Earth's inner radiation belt

The Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) is a time-of-flight versus energy spectrometer, the most prominent feature of which is the sensor known as the “puck” (because of its resemblance to a hockey puck). 

RBSPICE measures medium energy protons, electrons, and ions (H+, He+, and O+) as functions of energy and angle, and is capable of measuring the full range of expected ring current energies, intensities, and ion compositions from quiet conditions to extreme events, with a factor of ten margin against intensity saturation. 

Credit: NASA/JHUAPL

Scientists have discovered a new, persistent structure in Earth's inner radiation belt using data from the twin NASA Van Allen Probes spacecraft.

Most surprisingly, this structure is produced by the slow rotation of Earth, previously considered incapable of affecting the motion of radiation belt particles, which have velocities approaching the speed of light.

Two giant belts of radiation surround Earth. The inner belt is dominated by electrons and the outer one by protons. 

Credit: NASA

Data from the Van Allen Probes Ion Composition Experiment (RBSPICE) on board each of the twin spacecraft orbiting Earth revealed that the highly energized population of electrons of the inner radiation belt is organized into very structured patterns that resemble slanted zebra stripes.

Scientists had previously believed that increased solar wind activity was the primary force behind any structures in our planet's radiation belts.

These zebra stripes were shown to be visible even during low solar wind activity, which prompted a search for a new physical mechanism of their generation.

That quest led to the surprising discovery that the stripes are caused by rotation of Earth. The findings are reported in the March 20 issue of the journal Nature.

"It is because of the unprecedented high energy and temporal resolution of our energetic particle experiment, RBSPICE, that we now understand that the inner belt electrons are, in fact, always organized in zebra patterns," said Aleksandr Ukhorskiy of the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Md., co-investigator on RBSPICE and lead author of the paper.

"Furthermore, our modeling clearly identifies Earth's rotation as the mechanism creating these patterns. It is truly humbling, as a theoretician, to see how quickly new data can change our understanding of physical properties."

More information: Nature paper dx.doi.org/10.1038/nature13046