A picture of an aurora caused by electrons colliding with molecules in the Earth’s atmosphere. Credit: Jason Arhns, CC BY-NC-SA 2.0

High above the Earth’s surface, high-energy electrons and ions rain down on the atmosphere, spiraling along the planet’s magnetic field lines. When they strike the upper atmosphere, they can excite or ionize nitrogen and oxygen molecules and produce glowing displays of auroras. However, one way to study this behavior in even greater detail is to inject the electrons artificially with a spaceborne particle accelerator.

That’s what Marshall et al. consider in a new study, which uses computer simulations to explore the capabilities of a small, but powerful, particle accelerator positioned at an altitude of 300 kilometers, aimed at the atmosphere.

NASA has previously flown devices that fired beams with energies of a few to tens of kiloelectron volts, but the authors explore the effects of an accelerator 3 orders of magnitude stronger. The device would be capable of producing a beam with particles in the 0.5–10 million electron volt range in pulses lasting 0.1 microsecond and carrying 0.1 amp of current. These simulated specs are based on the Compact Particle Accelerator for Space Science (COMPASS), an instrument currently being designed by the SLAC National Accelerator Laboratory and the nonprofit research institute SRI International, both in Menlo Park, Calif.

The authors say that employing such instrumentation would offer many scientific opportunities to study the behavior of particles in the upper atmosphere. The paths of the electrons would trace out the arcing field lines of Earth’s magnetic field, illustrating how they bend and snap during the intense geomagnetic activity caused by solar storms. As they descend into the Earth’s atmosphere, some of the electrons would strike atmospheric molecules, producing visible aurora-like emission. Furthermore, a particle accelerator might even be capable of triggering lightning in the upper atmosphere, including some of its more exotic forms such as red sprites and blue jets.

The team’s modeling finds that the beam would leave a visible glowing trail that could be measured from the ground, with the peak emission occurring at an altitude of 44 kilometers. As the incoming electrons are jerked around by the atmosphere’s molecules, they would also emit X-rays that could be seen from high-altitude balloons operating around 44 kilometers. The authors say that demonstrating the feasibility of detecting these signatures is a step toward the construction and deployment of such an instrument. (Journal of Geophysical Research: Space Physics, doi:10.1002/2014JA020427, 2014)

—Mark Zastrow, Freelance Writer

Citation: Zastrow, M. (2015), Particle accelerator in space could help scientists study auroras, Eos, 96, doi:10.1029/2015EO027317. Published on 8 April 2015.

Text © 2015. The authors. CC BY-NC 3.0
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