Washington: NASA's Van Allen Probes, which was launched on Aug. 30, 2012, to study two giant belts of radiation that surround Earth, has shown scientists something that would require rewriting textbooks.
Just three days after its launch, the scientists on the mission made a decision to turn on the Relativistic Electron Proton Telescope (REPT) early in order that its observations would overlap with another mission called SAMPEX (Solar, Anomalous, and Magnetospheric Particle Explorer), that was soon going to de-orbit and re-enter Earth's atmosphere.
It was a lucky decision. Shortly before REPT turned on, solar activity on the Sun had sent energy toward Earth that caused the radiation belts to swell. The REPT instrument worked well from the moment it was turned on Sep. 1. It made observations of these new particles trapped in the belts, recording their high energies, and the belts' increased size.
Then something happened no one had ever seen before: the particles settled into a new configuration, showing an extra, third belt extending out into space.
"By the fifth day REPT was on, we could plot out our observations and watch the formation of a third radiation belt," said Shri Kanekal, the deputy mission scientist for the Van Allen Probes at NASA's Goddard Space Flight Center in Greenbelt, Md. and a coauthor of a paper on these results.
"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," he said.
Incorporating this new configuration into their models of the radiation belts offers scientists new clues to what causes the changing shapes of the belts-a region that can sometimes swell dramatically in response to incoming energy from the Sun, impacting satellites and spacecraft or pose potential threats to manned space flight.
The radiation belts, or Van Allen belts, were discovered with the very first launches of satellites in 1958 by James Van Allen. Subsequent missions have observed parts of the belts-including SAMPEX, which observed the belts from below-but what causes such dynamic variation in the belts has remained something of a mystery. Indeed, seemingly similar storms from the Sun have at times caused completely different effects in the belts, or have sometimes led to no change at all.
In its first six months in orbit, the instruments on the Van Allen Probes have worked exceptionally well and scientists are excited about a flood of observations coming in with unprecedented clarity. This is the first time scientists have been able to gather such a complete set of data about the belts, with the added bonus of watching from two separate spacecraft that can better show how events sweep across the area.
Spotting something new in space such as the third radiation belt has more implications than the simple knowledge that a third belt is possible. In a region of space that remains so mysterious, any observations that link certain causes to certain effects adds another piece of information to the puzzle.
Baker likes to compare the radiation belts to the particle storage rings in a particle physics accelerator. In accelerators, magnetic fields are used to hold the particles orbiting in a circle, while energy waves are used to buffet the particles up to ever faster speeds. In such accelerators, everything must be carefully tuned to the size and shape of that ring, and the characteristics of those particles.
The Van Allen Belts depend on similar fine-tuning. Given that scientists see the rings only in certain places and at certain times, they can narrow down just which particles and waves must be causing that geometry. Every new set of observations helps narrow the field even further.
"We can offer these new observations to the theorists who model what's going on in the belts. Nature presents us with this event-it's there, it's a fact, you can't argue with it-and now we have to explain why it's the case. Why did the third belt persist for four weeks? Why does it change? All of this information teaches us more about space," stated Kanekal.
The scientists published their results in a paper in the journal Science on Feb. 28, 2013.
First Published: Friday, March 01, 2013, 10:36