Earlier this week, NASA’s Van Allen probes mission (formerly known as the Radiation Belt Storm Probes) made the announcement that a third radiation belt has been discovered around the Earth in addition to the two that were previously known.
Launched at the end of August 2012, the Van Allen Probes are designed to look at the Van Allen Belts of Earth – a vast soup of charged particles that are held in place by the Earth’s magnetic field. The probes orbit the Earth in a highly elliptical orbit that passes through all of this charged particle soup, coming closest to the Earth at a height of about 700km and then out to the furthest extent of the belts at around 37,000km away. The probes have been providing valuable scientific data almost from day one and this discovery is no exception – although like a lot of other discoveries it involved a lot of good luck.
A few days after launch, some scientists asked for one of the probes’ instruments (the Relativistic Electron Proton Telescope) to be switched on early in order to overlap the VAP’s observations with that of another craft called SAMPEX (Solar, Anomalous, and Magnetospheric Particle Explorer) that was due to come to an end and burn up in the atmosphere quite soon at the time.
On the same day of the launch, the Sun had produced a giant prominence, shooting charged particles and a shockwave into space. Thanks to the scientists’ lobbying for the REPT to be turned on early, the Van Allen Probes watched as these charged particles from the Sun swarmed into the Van Allen Belts and made them swell in size before spontaneously creating a third belt above those that were already known. This new belt lasted for about four weeks before a shockwave from the Sun, caused by a coronal mass ejection on September 28th, destroyed its cohesion.
The discovery of the third belt and its transient nature poses many questions, as similar events on the Sun have produced either different effects or no change at all in the belts. The third belt might just be down to being in the right place at the right time with the right conditions, as it seems that the initial shockwave from the Sun aided the creation of the third belt while a second one destroyed it.
The observations have lead to astrophysicists updating their computer models to try and anticipate future spontaneous belt creation and the exact processes that drives it.
The study, “A Long-Lived Relativistic Electron Storage Ring Embedded in Earth’s Outer Van Allen Belt” by Baker, Kanekal, Hoxie et al, appeared in the Journal Science on Feb 28th.
Image Credit: Artist’s impression of VA probes in orbit around Earth – JPL/NASA