Probing Earth’s Radiation Belts
NASA's Van Allen Probes mission was designed to uncover details about Earth’s Van Allen Belts, two invisible, donut-shaped rings that surround Earth, one closer and the other farther. Discovered in 1958 by James Van Allen, each belt is filled with high-energy particles that bounce, rotate and drift through this region of space, sometimes producing spectacular visible spectacles, such as the auroras during space weather events like geomagnetic storms. But some space weather can also disrupt satellites used for communication and navigation as well as cause failures in Earth’s power grids.
Part of NASA’s Living With a Star program, Van Allen Probes was the first mission to use two spacecraft in tandem to study Earth’s radiation belts. By having two spacecraft with identical instruments speeding through the belts at roughly 2,000 mph (3,200 kph), with one followed by the other along nearly the same path, researchers could measure changes that occur in Earth’s radiation belts over time and through space, providing insights into the physical dynamics of the radiation belts and changes that occur in this critical region of space.
The probes measured the particles, waves, magnetic fields and electric fields that fill geospace, the region around Earth that includes its upper atmosphere, ionosphere and magnetosphere. As each probe ran out of fuel, Van Allen Probe B was deactivated July 19, 2019, and Van Allen Probe A was deactivated October 19, 2019, bringing the mission to a close.
Spacecraft and Instruments
Built, managed and operated at APL, the Van Allen Probes were designed to operate entirely within the radiation belts, enduring years of harsh radiation and continuous operation under conditions that would force other spacecraft to shut down. Each spacecraft was equipped with a suite of five instruments, including particle detectors to characterize the various ions and electrons in the radiation belts, an instrument to study the electric fields created by the motion of charged particles in near-Earth space and an instrument to investigate the role of magnetic fields and plasma waves in accelerating the particles to extremely high energies.
Results and Expectations
The Van Allen Probes enabled the discovery of the processes that accelerate and transport electrons and charged atoms called ions in the radiation belts, and what conditions lead to that transport. They helped scientists understand and quantify the loss of electrons from the radiation belts and determined the balance between competing processes that accelerate those particles or cause them to be lost to space. The probes also provided a deeper understanding of how the radiation belts change during geomagnetic storms.
More than 700 studies have used data collected by the Van Allen Probes.
August 30, 2012
End of Mission
October 18, 2019
Nelofar Mosavi, Johns Hopkins APL
Sasha Ukhorskiy, Johns Hopkins APL
Jim Spann, NASA Marshall Space Flight Center
David Sibeck, NASA Goddard Space Flight Center