Van Allen radiation belt

A region of Earth’s magnetosphere where energetic charged particles are trapped by the planet’s magnetic field. The belts vary in intensity and shape as solar activity and geomagnetic conditions change.

Magnetosphere: The region around a celestial body where its magnetic field influences charged particles and plasma. The radiation belts occupy part of Earth’s magnetosphere.
Explorer 1: The first United States satellite, launched in 1958, which carried instruments for measuring cosmic rays. Its measurements provided the first evidence of intense trapped radiation around Earth.
Radiation hardening: The design of electronic components and systems to tolerate exposure to ionizing radiation. Spacecraft crossing the belts need electronics that withstand particle damage.
Cosmic ray: A high-energy particle arriving from space, typically originating beyond the Solar System or in solar activity. Unlike belt particles, cosmic rays generally pass through the magnetosphere rather than remaining trapped.
Magnetic mirror: A magnetic-field configuration that reflects charged particles where field strength increases along their paths. Increasing field strength near Earth’s poles helps trap belt particles.
James Van Allen: An American physicist who led the design of instruments that discovered Earth’s radiation belts. His team interpreted Explorer 1 measurements as evidence of the belts.
Van Allen Probes: A NASA mission of twin spacecraft that studied the structure and dynamics of Earth’s radiation belts from 2012 to 2019. The probes measured particle populations and processes inside the belts.
Aurora: Light emitted in a planet’s upper atmosphere when energetic particles excite atmospheric atoms and molecules. Auroras arise from particles precipitating into the atmosphere, not from particles remaining trapped.
Adiabatic invariant: A physical quantity that remains approximately constant when a system changes slowly relative to its motion. Conservation of particle invariants helps explain repeated bouncing and drifting in the belts.
Sputnik 2: A Soviet satellite launched in 1957 that carried instruments for measuring radiation and other space conditions. Its radiation measurements contributed to the early evidence for trapped particles.

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