Karelitz 1 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
Karelitz 2 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
Karelitz 3 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
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). Karelitz 4 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 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 Figure 6: Solar Energetic Particles The snow on the Solar and Heliospheric natural defense mechanism: the magnetic field. This natural force Observatory (SOHO) spacecraft is actually SEPs hitting the device. The SEP event was emitted by the Earth is able to protect our planet from most solar 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. their
Karelitz 5 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.
Karelitz 6 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 Feb 2013. <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/>.