NASA's Van Allen Probes Capture Solar Shockwave for the First Time Ever

For the first time ever, NASA's Van Allen probes have caught a solar shockwave in the act. On Oct. 8, 2013, an explosion on the sun's surface sent a supersonic blast wave of solar wind out into space and now, the twin spacecraft have captured the effects of this shockwave before and after it struck.

"These are very lightweight particles, but they are ultrarelativistic, killer electrons-electrons that can go right through a satellite," said John Foster, one of the researchers, in a news release. "These particles are accelerated, and their number goes up by a factor of 10, in just one minute. We were able to see this entire process taking place, and it's exciting: We see something that, in terms of the radiation belt, is really quick."

Since August 2012, the Van Allen Probes have been orbiting within the Van Allen radiation belts. Their mission is to help characterize the extreme environment within the radiation belts so that scientists can create more resilient spacecraft and satellites. This also placed them in a prime position to observe the solar shockwave.

When the shockwave occurred, the first probe was in just the right position, facing the sun, to observe the radiation belts just before the shockwave struck the Earth's magnetic field. The second probe then caught up to the same position an hour later, and recorded the shockwave's aftermath.

Now, the researchers have analyzed the probes' data. As the solar shockwave made impact, it struck "a sledgehammer blow" to the protective barrier of Earth's magnetic field. Instead of breaking through, though, the shockwave effectively bounced away and generated a wave in the opposite direction in the form of a magnetosonic pulse, which is a powerful, magnetized sound wave that propagated to the far side of the Earth within a matter of minutes.

The researchers were also able to identify the mechanism that accelerated certain particles in the radiation belts. It turns out that if particles' velocities as they circle the Earth match that of the magnetosonic pulse, they are seemed "drift resonant." This means that they're more likely to gain energy from the pulse as it speeds thorugh the radiation belts. The longer a particle interacts with the pulse, the more it is accelerated, which creates an extremely high-energy particle.

"This was a relatively small shock. We know they can be much, much bigger," said Foster. "Interactions between solar activity and Earth's magnetosphere can create the radiation belt in a number of ways, some of which can take months, others days. The shock process takes seconds to minutes. This could be the tip of the iceberg in how we understand radiation-belt physics."

The findings are published in the Journal of Geophysical Research: Space Physics.

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