Magnetic storms near Earth can generate dazzling auroras — and they also release high-energy particles hazardous to spacecraft and astronauts. Our THEMIS mission witnessed one such event that was much closer to Earth than previously thought possible — only 3-4 Earth diameters away, well with the Moon’s orbit. This discovery will help scientists refine predictive models of how Earth’s magnetic environment responds to the Sun’s constant outpouring of material — the solar wind — providing advanced warning to prepare satellites, astronauts, and energy grids for particularly large magnetic storms.

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