Beyond Pluto

Astronomers spy a faint icy body at the solar system's edge -- evidence of the breeding grounds of comets

Where does the solar system end? At Pluto, most folks would reply. Or at Neptune, the cognoscenti might say, because thanks to Pluto's odd, egg-shaped orbit, the eighth planet has been outermost since 1979 and will be through 1998. But astronomers suspect that the sun's family actually extends far beyond either of these two planets. Out there in the frigid darkness beyond any known planet, they believe, lies the Kuiper belt, a ring of dusty ice chunks that surrounds the solar system. Beyond that, astronomers say, is the similarly composed Oort cloud, which forms a vast sphere around our planetary system....

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