Since their discovery in the late 1950's, the Van Allen Belts have been extensively mapped with spacecraft instrumentation, yet the
reason for their detailed 'double donut' shape has remained illusive. Between the Inner and Outer Belts, a 'Slot Region' exists in which
energetic electrons and protons seem to be missing. The reason for this may now be at hand. Space physicists have known for decades that energetic particles can be affected by low-frequency, electromagnetic plasma
waves, and by radio waves beamed into space from ground-based transmitters. IMAGE scientists have now discovered that Nature may use a similar process to evacuate the Slot Region.
Maps of plasmaspheric 'hiss' using IMAGE RPI data match the statistical, geographic distribution of lightning.
These observations strongly support lightning as the dominant source for plasmaspheric hiss, which
through wave-particle interactions, maintains the slot region virtually free of energetic particles in the radiation belts. If
independently confirmed, this result will resolve a 38-year controvercy about the source
of the plasmaspheric hiss.
(2004: Green et al.)
Related IMAGE Discoveries
Plasmasphere -An extension of Earth's upper atmosphere and ionosphere into space. This material is a charged plasma with particle energies below 100 electron Volts. The plasma is anchored to Earth's magnetic field and is dragged into a
24-hour 'co-rotational' orbit out to 10,000 kilometers or more.
Slot Region -A region in the Van Allen radiation belts several thousand kilometers wide,
located at about 2 Earth-radii, where a noticible lack of
energetic electrons and protons has been identified. It is a popular location for some satellites due to the greatly lowered density of particle radiation that normally damage spacecraft in other parts of the Van Allen belts.
Useful Web Resources
Dr. S. Odenwald, firstname.lastname@example.org,
NSSDC, Mail Code 630, NASA Goddard Space Flight Center,
Greenbelt, MD 20771
NASA Approval: J. L. Green, James.Green@nasa.gov
Rev. 1.0.0, 24
July 2004, EVB II