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Solar Energetic Particles: A Relay Race to Earth
By Andrea Karelitz
Things move fast.
If you’re feeling daring, take a trip to Brazil and speed down the fastest water slide in the world at
65 mph, or take a joyride in the TKR, a 1005 horsepower supercar that can travel 270 mph. Rather fly? Catch a
4,500 mph ride on the North American X-15 rocket powered aircraft. Or you could try catching up with New
Horizons, the NASA Robotic Mission venturing to Pluto, so you can travel over 36,360 mph as you soar to space.
Still not fast enough to get the rush you’re looking for? Then you should consider a more natural form of
transportation– solar energetic particles (SEPs). These highly energized particles, a phenomenon of the sun, travel
6,596 times faster than the NASA Pluto Mission as they race along the heliosphere and head towards Earth or
neighboring planets.
Reaching speeds nearly 80 percent of the speed of light, these natural plasmatic vehicles are composed of
protons, electrons and neutrons and have temperatures greater than several million Kelvin, according to Dr.
Edward Cliver, a research scientist at the Air Force Research Lab. Think that’s impressive? What if I told you that
each particle is about 1.7 x 10-15 m in size, at the very biggest, yet collectively they have the energy to knock out
the entire New York City power grid or cause the remarkable aurora borealis, seen in Figure 1.
Figure 1: Aurora Borealis
The aurora borealis, or Northern Lights, are considered one of the seven
natural wonders of the world and are a by-product of energy emitted from
the sun. The aurora pictured occurred on February 15, 2012 in Yukon,
Alaska.
Photo credit: Jason Ahrns
But how exactly do these tiny high energy and erratic particles travel from our sun to create marvelous
light shows in Alaska or cause ATM machines to go haywire and prohibit you from accessing your funds?
The sun’s solar core is the key to the particles’ remarkable high strung journey into our atmosphere via
the heliospheric highway. The core is our own personal battery; however, it has more juice than your average
AAA alkaline battery that powers your TV remote—about 386 billion megawatts more! This hefty amount of
energy is able to force hydrogen protons, which normally do not like each other, to interact and undergo a process
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known as nuclear fusion. By doing this, the sun transforms 700,000,000 tons of hydrogen atoms to 695,000,000
tons of helium and 5,000,000 tons of energy in the form of gamma rays or energetic light photons, every second,
according to Carl G. Looney, author of “Climate Change: What Does the Science Say?” The energy created is
now absorbed and re-emitted through the different layers of the sun, seen in Figure 2.
Figure 2: Layers of the Sun
The layers include the core, radiative zone, convective
zone, chromospheres, photosphere, and corona. Some of
the energy that is created in the core is absorbed in the
different layers as it propagates outward.
Source: Knowledge Allocator
As the energy propagates, it’s like millions of preschoolers who are lined up along the solar radius and are
passing along a photon relay stick. After the energy reaches the solar surface, the SEPs are fueled on their
92,955,807 mile journey to the Earth. Two distinct events that are theorized to provide the particles with enough
fuel for their long journey: a solar flare and a coronal mass ejection. A solar flare, shown in Figure 3, is an
explosive burst of magnetic energy in the form of light and radiation.
Figure 3: Solar Flare
This bright spot in the image is a solar flare that
occurred on February 11, 2011. A typical solar
flare lasts around an hour. The image was taken by
the Solar Dynamics Observatory (SDO).
Source: NASA Goddard Space Flight Center
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This explosive burst occurs impulsively as the energy deep within the core is brought up to the surface.
The released energy is in the form of electromagnetic radiation, which includes the majority of the light spectrum
from high frequency gamma-rays to low frequency radio waves, according to Dr. Alex Young, the Associate
Director of the Heliosphysics Science Division at NASA Goddard Space Flight Center (GSFC). Since SEPs are
accelerated immediately by the same energy that fuels the burst of light, they can reach very high speeds, very
quickly.
A coronal mass ejection (CME) is the second way SEPs can be accelerated. Like a solar flare, a CME also
occurs when the magnetic energy at the surface builds up due to the rising energy from the core. But with a CME,
billions of tons of solar material, in the form of plasma, are thrown into the heliosphere. The heliosphere is the
sun’s magnetic field region, according to Dr. Young. The CME races in the direction it was ejected at speeds
reaching 3000 km per second. As it propagates it accelerates SEPs in front of it. By using tools like a
chronograph, as seen in Figure 4, NASA GSFC Space Weather Research Center forecasters work to forecast SEP
events based on CMEs.
Figure 4: Coronal Mass Ejection
The CME shown above in the chronograph occurred on January 23, 2012 and
was taken by STEREO B spacecraft. The Earth is to the right in this image. A
chronograph is used to block the intense light from the sun so space weather
forecasters are better able to predict the speed and direction of the CME.
Source: NASA GSFC
If a CME is Earth directed, like the January 23 event pictured in Figure 4, the speed of the CME is directly
related to the peak flux of the SEP event that it causes, according to Andrea Karelitz in “The Correlation of
Coronal Mass Ejections and Solar Energetic Particles.” In general, the faster the CME, the greater the peak flux
the SEP event will be. The exact reason behind solar flares and CMEs still puzzles many solar physicists, but the
majority of them agree that both events can energize SEPs, explains Antti Pulkkinen, a research scientist at NASA
GSFC.
After being accelerated, SEPs are guided along their journey by the sun’s solar wind, as seen in Figure 5.
Unlike the wind we’re familiar with, the sun’s solar wind is a continuous stream of particles and magnetic field
released from the sun. Another difference between the sun’s solar wind and the strong 20 mile per hour wind gust
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you may have felt outside is that the solar wind travels about a million miles per hour, according to David
Hathaway from NASA Marshall Space Flight Center (MSFC).
Figure 5: The Sun’s Solar Wind and Earth’s Magnetic Field
The solar wind serves as a direct path for solar events to reach the earth. SEPs are guided along the sun’s
solar wind until a planet, spacecraft, or another entity stops them in their path.
Source: ScienceArt.co.uk
their
The speed of SEPs depends on how they’re fuelled. For example, if solar flares excite them, they’re more likely to
move faster because the light solar flares produce travels at the speed of light. SEPs journey through the
heliosphere (which is the area in space that the sun’s solar wind reaches) to Earth takes anywhere from twenty
minutes to a few days, according to NOAA Space Weather Prediction Center.
But it may take longer because SEPs are susceptible to a few roadblocks along their journey. And just like
preschoolers in a relay race, even though they aren’t trying to break things, their mission to the Earth can cause
some damage if they run into anything breakable. If spacecraft or GPS
satellites happen to be in their way, the SEPs will “snow” on the
devices, Dr. Pulkkinen explains. As seen in Figure 6, this snow isn’t
quite the harmless white flakes that flourish State College during the
winter. The snow that the spacecraft and satellites experience from a
SEP event can cause malfunctions and equipment failure due to the
high energies of the particles. For this reason, it’s extremely important
for satellite and spacecraft operators to be able to predict and forecast
solar flares and CMEs so they can “childproof” their device and put
them in safe mode to avoid damages.
Even though SEPs can wreak havoc, the Earth does have a
natural defense mechanism: the magnetic field. This natural force
The ‘snow’ on the Solar and Heliospheric
Observatory (SOHO) spacecraft is actually
emitted by the Earth is able to protect our planet from most solar
SEPs hitting the device. The SEP event was
cause by a CME on January 23, 2012.
events; the magnetic field around Earth acts as an electromagnetic
Source: NASA GSFC
barrier by blocking most particles. SEPs are forced to change paths so
they’re now traveling along Earth’s magnetic field lines. They follow these field lines until they eventually reach
the origin, or the North or South Poles, and this creates the miraculous Northern or Southern Lights, as shown in
Figure 7.
Figure 6: Solar Energetic Particles
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Figure 7: Aurora Forecast Area
The green areas in this model show the predicted area of
visible aurora borealis from a March 9, 2012 SEP event.
Source: NOAA Space Weather Prediction Center
These lights are the SEPs that interact with oxygen and nitrogen atoms in Earth’s atmosphere. The interactions
occur at altitudes 20-200 miles above Earth’s surface, according to Dr. Young, and are usually only visible in the
upper and lower altitudes, as seen in the aurora forecast.
But what happens with the particles that have enough energy to break through the magnetic field? Some
of the very high energy SEPs will have the energy needed to work their way past the magnetic field and into
Earth’s atmosphere. These particles can cause power grid problems by inducing current. Or they may interact with
charged particles in our ionosphere and obstruct satellite communication signals. According to Bill Murtagh,
Program Coordinator of the NOAA Space Weather Prediction Center, when this happens, SEPs have the
capability to disable many electronic devices that rely on these signals, such as ATM machines, gas pumps, and
GPS units.
Next time your lights flicker, don’t be so quick to assume a car speeding down the road hit a light pole and
knocked out your power. It may be a faster culprit wreaking havoc on your power.
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Works Cited
Cliver, E.W., and A. G. Long. "Electrons and Protons in Solar Energetic Particle Events." Astrophysical
Journal. 658 (2007): 1349-1355. Print. <http://iopscience.iop.org>.
Hathaway, David H.. "Solar Physics." The Solar Wind. NASA Marshall Space Flight Center, n.d. Web.15 Feb
2013. <http://solarscience.msfc.nasa.gov>.
Heliophysics Science Divsion. NASA Goddard Space Flight Center. Web. 15 Feb 2013.
<http://science.gsfc.nasa.gov>.
Karelitz, Andrea M., and Antti A. Pulkkinen. "The Correlation of Coronal Mass Ejections and Solar Energetic
Particles." Space Weather Journal. (pending approval)
Looney, Carl G. Climate Change: What Does the Science Say?. United States of America: 180. Print.
Solar Wind and Earth's Magnetic Field. 2011. Science Art.co.uk, United Kingdom. Web. 15 Feb 2013.
<http://www.scienceart.co.uk>.
Space Weather Prediction Center. National Weather Service. Web. 15 Feb 2013.
<http://www.swpc.noaa.gov/>.
"Will The Sun Shine Forever." Knowledge Allocator. Knowledge Allocator, 27 Jan 2011. Web. 15 Feb2013.
<http://www.knowledgeallocator.com>.
Young, Alex, ed. The Sun Today. NASA Goddard Space Flight Center, n.d. Web. 15 Feb 2013.
<http://www.thesuntoday.org/>.