科学美国人60秒:Third Van Allen Belt Came and Went

Back in 1958, at the dawn of the space age, physicist James Van Allen discovered that the Earth is ringed by high-energy charged particles. Held in place by the planet’s magnetic field, these bands of radiation were named the inner and outer Van Allen Belts. They’re of particular interest to NASA as they pose a potential danger to spacecraft.

Now a NASA mission also named for Van Allen has found something new about his belts. By looping through them repeatedly, the twin Van Allen Probes discovered a third band of radiation.

Or at least there were three. The two spacecraft uncovered the previously unknown structure in September. It consisted of fast-moving electrons, situated between the two previously known Van Allen Belts. The discovery was reported in the journal Science. [Daniel N. Baker et al., A Long-Lived Relativistic Electron Storage Ring Embedded in Earth's Outer Van Allen Belt]

But the new structure is no longer. Four weeks after the probes found it, the third ring was wiped out by a strong shock wave emanating from the sun. Still, the unexpected finding shows that the Van Allen Belts are more complex and variable than had been assumed. And that seemingly well-established knowledge about space still may have the capacity to surprise.

—John Matson