When the Van Allen probes observed high energy electrons, the radiation belt looked like just what we thought it would like in the illustration above. But when it looked at low energy electrons, the inner donut looked much chunkier than the outer one, like so:
When the probes looked at electrons with the highest energy, though, they saw an outer donut separated from Earth only by an empty space:
Finally, geomagnetic storms completely mess up the radiation belt and the whole region could be completely filled with low-energy electrons:
We've only found this out now because older instruments could only measure a handful of energy levels; the new probes are capable of measuring hundreds at once. Plus, they filter out background noise in the form of protons very well. The space agency deployed the probes back in 2012 in an effort to protect our satellites. By knowing which orbits expose satellites to radiation the most, scientists will be able to make adjustments and ensure they don't die an early death.
[Image credit: NASA Goddard/Duberstein]