The Outer Limits

How a passion for comets led a Texas astronomer to redefine the solar system—and turned her into a big star.

For a long time astronomers have wondered what else lies in the far reaches of the solar system, still to be discovered. Jupiter and Saturn are so big that they are hard to miss, but the cold nether region that lies beyond—where Uranus, Neptune, and lonely, distant Pluto circles the sun—has always been a puzzle. Pluto is the second smallest of the solar system’s nine planets, and it lies about 3.7 billion miles from Earth. It wasn’t discovered until 1930. Early in 1993 Anita Cochran, an astronomer at the University of Texas at Austin, learned that the faulty lens of the Hubble Space Telescope was being repaired and hoped that the instrument might produce some answers.

Cochran and a team of three other astronomers were able to obtain time on the newly refurbished telescope, and this past June, at a meeting of the American Astronomical Society in Pittsburgh, they announced their findings: Using images beamed down from the biggest telescope in space, they had found firm evidence of a long-suspected belt of comets that begins beyond the planet Neptune and extends out into space for billions of miles. High school science textbooks describe a solar system in which everything comes to an abrupt halt after Pluto. Cochran’s discovery, however, proves that this model of the solar system is wrong—the solar system doesn’t suddenly cease, it peters out in a vast stretch of cosmic rubble.

Anita Cochran has shoulder-length brown hair, direct blue eyes, and wears oversized glasses. She talks about her work with the full-tilt enthusiasm that other people reserve for sports teams. “I’m like a kid,” she says. “I get paid

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