March 1st, 2013 by Michael Ricciardi
Calling the discovery a “lucky one” and “entirely unexpected”, NASA planetary scientists have announced their discovery of an ephemeral (transient) third ring of radiation surrounding our planet. The new radiation band is actually a torus-shaped ring, and was detected by a pair of space probes — the Van Allen probes (named after the astronomer that first discovered the radiation belts) — carrying an instrument called the Relativistic Electron Proton Telescope (REPT).
Following a request by planetary scientist Daniel Baker to activate the instrument earlier than scheduled (to compare its data with the SAMPEX probe’s data), the telescope almost immediately began detecting high energy particles trapped in the two known Van Allen belts.
However, what caught the scientists by surprise was that, over the course of several days, those particles began to settle into a never before seen configuration: a third, high-energy band embedded within the outermost Van Allen belt which is located about 17,000 to 20,000 km (about 12,000 to 14,000 miles) above the Earth’s surface.
At first, scientist thought that their instruments were malfunctioning. According to Shri Kanekal, deputy mission scientist for the Van Allen Probes;
We started wondering if there was something wrong with our instruments, We checked everything, but there was nothing wrong with them. The third belt persisted beautifully, day after day, week after week, for four weeks.
But a second surprise was awaiting the scientists: on October 1, the mysterious third belt vanished — “virtually annihilated” itself — believed due to a powerful shock wave caused by the solar wind.
Many mission scientists believe that the timing of the third ring’s formation — coming as it did shortly after a massive solar eruption on August 31, 2012 (and captured by NASA’s SDO satellite) — was not coincidental; the solar eruption may have helped trigger its formation.
It is known that these belts swell and shrink in response to changes in the solar wind, but exactly how this happens is not entirely understood. This most recent discovery may aid scientists in unravelling this mystery.
Quoting from the published abstract:
In situ energy-specific and temporally resolved spacecraft observations reveal an isolated third ring, or torus, of high-energy (E > 2 MeV) electrons that formed on 2 September 2012 and persisted largely unchanged in the geocentric radial range of 3.0 to ~3.5 Earth radii for over four weeks before being disrupted (and virtually annihilated) by a powerful interplanetary shock wave passage.
It is no doubt an instructive development for space scientists, as this discovery comes more than fifty years after the Van Allen belts were discovered; the discovery of radiation belts is considered the very first discovery of the Space Age. Their Earth-enveloping presence and activity has been a “given” ever since. And yet, we are learning that even this “common” feature of our planetary space can still hold surprises for us.
It is not known if and when this third radiation belt (or “Relativistic Electron Storage Ring”) will reappear.
The Van Allen probes mission findings are published in this week’s issue of Science under the title: ‘A Long-Lived Relativistic Electron Storage Ring Embedded in Earth’s Outer Van Allen Belt’
Source Material for this post came from the io9.com for this story NASA: “We’ve discovered a previously unknown surprise circling Earth” By Robert T. Gonzalez
Top Image: io9.com
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