Space Radiation Highlights

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Our planet is nestled in the center of two doughnut-shaped regions of powerful, dynamic radiation: the Van Allen belts, where high-energy particles are trapped by Earth’s magnetic field. Depending on incoming radiation from the sun, they can gain energetic particles. On the other hand, the belts can lose energized particles too.

We are familiar with rapid changes in weather, and the radiation belts can experience these too – particles can be depleted by a thousand-fold in mere hours. These dramatic loss events are called drop-outs, and they can happen when intense bouts of solar radiation disturb Earth’s magnetic environment. There have been many theories on how this happens, but scientists have not had the data to pinpoint which one is correct.

However, on Jan. 17, 2013, NASA's Van Allen Probes were in just the right position to watch a drop-out in progress and resolve a long-standing question as to how the lower region of the belts close to Earth loses high-energy electrons – known as ultra-relativistic electrons for their near-light speeds. During a drop-out, a certain class of powerful electromagnetic waves in the radiation belts can scatter ultra-relativistic electrons. The electrons stream down along these waves, as if they are raining into the atmosphere. A team led by Yuri Shprits of University of California in Los Angeles published a paper summarizing these findings in Nature Communications on Sept. 28, 2016.

Such information helps illustrate the complexity of Earth's magnetic surroundings. Understanding changes within the belts is crucial for protecting the satellites and astronauts travelling through this sometimes harsh space environment.

Credit: NASA/Joy Ng/Martin Rother/GFZ-Potsdam

Music Credits: Translucent Nature by Anthony Phillips [PRS], Samuel Karl Bohn [PRS] from the KillerTracks catalog.

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Along with the visible light and warmth constantly emitted by our sun comes a whole spectrum of X-ray and ultraviolet radiation that streams toward Earth. A new CubeSat – a miniature satellite that provides a low-cost platform for missions – is now in space observing a particular class of X-ray light that has rarely been studied.

On June 9, 2016, the NASA-funded, bread loaf-sized Miniature X-Ray Solar Spectrometer, or MinXSS, CubeSat began science operations, collecting data on soft X-rays. Watch the video to see a low-intensity solar eruption – a solar flare – from July 21, 2016. The flare imagery was captured by NASA's Solar Dynamics Observatory; the MinXSS data shown on the right shows the soft X-rays observed in near-Earth space by the CubeSat before and during the flare.

Each type of solar radiation conveys unique information about the physics underlying solar flares. This data reveals the temperature, density and abundance of solar flare material, all critical factors for determining how flares evolve and heat the sun’s atmosphere. Ultimately, solar eruptions impact Earth’s upper atmosphere: X-rays from the sun can disturb near-Earth space, interfering with GPS, radio and other communication signals. The class of X-rays that MinXSS observes are particularly important for their influence in the level of the upper atmosphere called the ionosphere.

This video shows how dynamic the solar atmosphere can become, and highlights that MinXSS has great sensitivity to observe even the weak flares. These observations exemplify the goals of the six-month mission, which began after the spacecraft was deployed from the International Space Station in May 2016 and has already met its criteria for comprehensive success. The University of Colorado, Boulder manages MinXSS under the direction of principal investigator Tom Woods.

Credit: NASA’s Goddard Space Flight Center/LASP/MinXSS/SDO/Joy Ng

Music Credits: Sagacity by Christian Telford [ASCAP], David Travis Edwards [ASCAP], Robert Anthony Navarro [ASCAP] from the KillerTracks catalog

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In addition to the constant emission of warmth and light, our sun sends out occasional bursts of solar radiation that propel high-energy particles toward Earth. These solar energetic particles, or SEPs, can impact astronauts or satellites. To fully understand these particles, scientists must look to their source: the bursts of solar radiation.

But scientists aren’t exactly sure which of the two main features of solar eruptions –narrow solar flares or wide coronal mass ejections – causes the SEPs during different bursts. Scientists try to distinguish between the two possibilities by using observations, and computer models based on those observations, to map out where the particles could be found as they spread out and traveled away from the sun. NASA missions STEREO and SOHO collect the data upon which these models are built. Sometimes, these solar observatories saw SEPs on the opposite side of the sun than where the eruption took place. What kind of explosion on the sun could send the particles so far they ended up behind where they started?

Now a new model has been developed by an international team of scientists, led by the University of Central Lancashire and funded in part by NASA. The new model shows how particles could travel to the back of the sun no matter what type of event first propelled them. Previous models assumed the particles mainly follow the average of magnetic field lines in space on their way from the sun to Earth, and slowly spread across the average over time. The average field line forms a steady path following a distinct spiral because of the sun’s rotation. But the new model takes into consideration that magnetic fields lines can wander – a result of turbulence in solar material as it travels away from the sun.

With this added information, models now show SEPs spiraling out much wider and farther than previous models predicted – explaining how SEPs find their way to even the far side of the sun. Understanding the nature of SEP distribution helps scientists as they continue to map out the origins of these high-energy particles. A paper published in Astronomy and Astrophysics on June 6, 2016, summarizes the research, a result of collaboration between the University of Central Lancashire, Université Libre de Bruxelles, University of Waikato and Stanford University.

This video compares the two models for particle distribution over the course of just three hours after an SEP event. The white line represents a magnetic field line, the general path that the SEPs follow. The line starts at am SEP event at the sun, and leads the particles in a spiral around the sun. The animation of the updated model, on the right, depicts a static field line, but as the SEPs travel farther in space, turbulent solar material causes wandering field lines. In turn, wandering field lines cause the particles to spread much more efficiently than the traditional model, on the left, predicted.

Credit: NASA’s Goddard Space Flight Center/UCLan/Stanford/ULB/Joy Ng

Music credit: The Voyage by Magnum Opus [ASCAP] from the KillerTracks Catalog