Far beyond Pluto, beyond even the comets, lies the solar system’s true edge—the heliosheath, where charged particles blowing outward from the sun crash into those flowing from other stars to create a vast protective magnetic bubble.
In September scientists produced the most comprehensive study yet of this distant boundary, finding it improbably dynamic. The observations come from NASA’s Interstellar Boundary Explorer (IBEX), which detects neutral atoms that are sent streaming toward Earth after breaking free from the heliosheath. In 2009 IBEX data revealed a long ribbon of those atoms, with a knot in it, crossing the sky. Just six months later, the knot had unwound.
Mission leader Dave McComas of the Southwest Research Institute in San Antonio says there is no good theory for why the heliosheath would be so jittery tens of billions of miles from the sun despite its tremendous size, or for why the ribbon even exists.
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