Data sent back from NASA's Pioneer 3 and Explorer IV spacecraft, both launched in 1958 and both carrying instruments built by James Van Allen,
showed the presence of two distinct rings of high-energy electrons.
This week, NASA scientists have announced the discovery of a third ring.
On Aug. 30, NASA launched the Radiation Belt Storm Probes
mission, since renamed the Van Allen Probes mission, to learn more
about the Van Allen belts--donut-shaped rings of so-called "killer
electrons" that encircle the Earth that were the first discovery of the
space age, and are known to be hazardous to satellites, astronauts and
technological systems on Earth.
Each probe carries a Relativistic Electron-Proton Telescope, or REPT, designed and built at CU-Boulder's Laboratory for Atmospheric and Space Physics,
known as LASP. When CU-Boulder scientists turned on the instruments,
just a few days after launch, they were shocked by what they saw unfold:
the formation of a third "storage ring" radiation belt.
"It was so odd looking, I thought there must be something wrong with the instrument," said LASP Director Dan Baker,
REPT principal investigator and lead author of the study published
online today in the journal Science. "But we saw things identically on
each of the spacecraft. We had to come to the conclusion that this was
real."
The data sent back to Earth from the REPT instruments during the
month of September initially showed two Van Allen belts, as expected.
But after a few days, the outer ring appeared to compress into an
intense, tightly packed electron band and a third, less compact belt of
electrons formed further out, creating a total of three rings. The
middle "storage ring" persisted as the belt furthest away from Earth
began to decay away in the third week of September, until, finally, a
powerful interplanetary shockwave traveling from the sun virtually
annihilated both the storage ring and the rest of the outer belt.
Scientists have known that the outer Van Allen belt can fluctuate
wildly, at times swelling with charged particles before letting them
slip away again, depending on space weather. In the months since the
storage belt and the outer belt virtually disappeared, the Van Allen
radiation zones have re-formed into the originally expected two-belt
structure.
"We have no idea how often this sort of thing happens," Baker said.
"This may occur fairly frequently but we didn't have the tools to see
it." The fact that NASA's new tools observed the events at all was
somewhat serendipitous. When NASA launches a new spacecraft, instruments
onboard are turned on, tested and calibrated in a prescribed order.
CU-Boulder's REPT instruments were originally scheduled to be turned
on about a month after launch, when the third Van Allen radiation belt
would have already dissipated. But Baker and his colleagues lobbied to
jump the REPT instrument to the front of the instrument commissioning
line.
Baker's concern was that the only other NASA sensors collecting similar —though far more rudimentary—data on the Van Allen radiation belts
were onboard the 20-year-old Solar, Anomalous and Magnetospheric
Particle Explorer, or SAMPEX, mission, which was expected to fall back
into Earth's atmosphere and burn up in late 2012. Baker wanted REPT to
collect as much overlapping data with SAMPEX as possible so that the two
data records could be more easily stitched together and compared with
each other.
The REPT researchers won their case, and the instruments powered up
on Sept. 1. "Had we not done so, we would have missed this," Baker said.
"It's good to be in the right place at the right time with the right
instrument."
The two NASA probes, which are flying around Earth in an elliptical
orbit, are able to send back observations for the first time from the
heart of the two belts as each probe passes through. The information
gathered by the twin, octagonal spacecraft will help researchers better
understand how space weather affects near-Earth phenomena by interacting
with, feeding and stripping away the Van Allen belts.
A better understanding of belt formation, including the number of
belts, will help researchers refine their understanding of how and when
solar storms can wreak havoc on Earth.
"We can offer these new observations to the theorists who model
what's going on in the belts," said Shri Kanekal, the deputy mission
scientist for the Van Allen Probes at NASA's Goddard Space Flight Center
in Greenbelt, Md. and a co-author of the new study. "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."
For more information: www.nasa.gov/vanallenprobes A Long-Lived
Relativistic Electron Storage Ring Embedded in Earth's Outer Van Allen
Belt," by D.N. Baker, Science, 2013.
www.sciencemag.org/content/early/2013/02/27/science.1233518.abstract
Journal reference: Science *
Image credit: NASA/Van Allen Probes/Goddard Space Flight Center
Source: The Daily Galaxy via University of Colorado at Boulder
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