2hrly gs ch p nasa's van allen probes discover a surprise circling earth
1. NASA's Van Allen Probes Discover a Surprise Circling
Earth
02.28.13
After most NASA science spacecraft launches, researchers wait patiently
for months as instruments on board are turned on one at a time, slowly
ramped up to full power, and tested to make sure they work at full
capacity. It's a rite of passage for any new satellite in space, and such a
schedule was in place for the Van Allen Probes when they launched on
Aug. 30, 2012, to study two giant belts of radiation that surround Earth.
But a group of scientists on the mission made a case for changing the
plan. They asked that the Relativistic Electron Proton Telescope (REPT)
be turned on early – just three days after launch -- 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. Within mere days of launch, the Van Allen Probes
showed scientists something that would require rewriting textbooks.
"By the fifth day REPT was on, we could plot out our observations and
watch the formation of a third radiation belt," says 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
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2. them. The third belt persisted beautifully, day after day, week after
week, for four weeks."
The scientists published their results in a paper in the journal Science on
Feb. 28, 2013. 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.
› View larger
Two giant swaths of radiation, known as the Van Allen Belts,
surrounding Earth were discovered in 1958. In 2012, observations from
the Van Allen Probes showed that a third belt can sometimes appear.
The radiation is shown here in yellow, with green representing the
spaces between the belts. Credit: NASA/Van Allen Probes/Goddard
Space Flight Center
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
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3. 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.
The Van Allen Probes consist of two identical spacecraft with a mission
to map out this region with exquisite detail, cataloguing a wide range of
energies and particles, and tracking the zoo of magnetic waves that pulse
through the area, sometimes kicking particles up to such frenzied speeds
that they escape the belts altogether.
"We've had a long run of data from missions like SAMPEX," says
Daniel Baker, who is the principal investigator for REPT at the
University of Colorado in Boulder and first author on the Science paper.
"But we've never been in the very throat of the accelerator operating a
few hundred miles above our head, speeding these particles up to
incredible velocities."
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,
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4. 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," says Kanekal. "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."
› View larger
On Aug. 31, 2012, a giant prominence on the sun erupted, sending out
particles and a shock wave that traveled near Earth. This event may have
been one of the causes of a third radiation belt that appeared around
Earth a few days later, a phenomenon that was observed for the very
first time by the newly-launched Van Allen Probes. This image of the
prominence before it erupted was captured by NASA's Solar Dynamics
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5. Observatory (SDO). Credit: NASA/SDO/AIA/Goddard Space Flight
Center
Scientists already have theories about just what kind of waves sweep out
particles in the "slot" region between the first two belts. Now they must
devise models to find which waves have the right characteristics to
sweep out particles in the new slot region as well. Another tantalizing
observation to explore lies in tracking the causes of the slot region back
even further: on Aug. 31, 2012, a long filament of solar material that had
been hovering in the sun's atmosphere erupted out into space. Baker says
that this might have caused the shock wave that led to the formation of
the third ring a few days later. In addition, the new belt was virtually
annihilated four weeks after it appeared by another powerful
interplanetary shock wave from the sun. Being able to watch such an
event in action provides even more material for theories about the Van
Allen belts.
Despite the 55 years since the radiation belts were first discovered, there
is much left to investigate and explain, and within just a few days of
launch the Van Allen Probes showed that the belts are still capable of
surprises.
"I consider ourselves very fortunate," says Baker. "By turning on our
instruments when we did, taking great pride in our engineers and having
confidence that the instruments would work immediately and having the
cooperation of the sun to drive the system the way it did – it was an
extraordinary opportunity. It validates the importance of this mission
and how important it is to revisit the Van Allen Belts with new eyes."
The Johns Hopkins University Applied Physics Laboratory (APL) built
and operates the twin Van Allen Probes. The Van Allen Probes comprise
the second mission in NASA's Living With a Star (LWS) program to
explore aspects of the connected sun-Earth system that directly affect
life and society. The program is managed by NASA Goddard.
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6. Observatory (SDO). Credit: NASA/SDO/AIA/Goddard Space Flight
Center
Scientists already have theories about just what kind of waves sweep out
particles in the "slot" region between the first two belts. Now they must
devise models to find which waves have the right characteristics to
sweep out particles in the new slot region as well. Another tantalizing
observation to explore lies in tracking the causes of the slot region back
even further: on Aug. 31, 2012, a long filament of solar material that had
been hovering in the sun's atmosphere erupted out into space. Baker says
that this might have caused the shock wave that led to the formation of
the third ring a few days later. In addition, the new belt was virtually
annihilated four weeks after it appeared by another powerful
interplanetary shock wave from the sun. Being able to watch such an
event in action provides even more material for theories about the Van
Allen belts.
Despite the 55 years since the radiation belts were first discovered, there
is much left to investigate and explain, and within just a few days of
launch the Van Allen Probes showed that the belts are still capable of
surprises.
"I consider ourselves very fortunate," says Baker. "By turning on our
instruments when we did, taking great pride in our engineers and having
confidence that the instruments would work immediately and having the
cooperation of the sun to drive the system the way it did – it was an
extraordinary opportunity. It validates the importance of this mission
and how important it is to revisit the Van Allen Belts with new eyes."
The Johns Hopkins University Applied Physics Laboratory (APL) built
and operates the twin Van Allen Probes. The Van Allen Probes comprise
the second mission in NASA's Living With a Star (LWS) program to
explore aspects of the connected sun-Earth system that directly affect
life and society. The program is managed by NASA Goddard.
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