The solar system was a cramped, provincial place in May 1989, and so was the Italian restaurant in downtown Baltimore where Alan Stern exhorted a dozen of his colleagues to join him on an improbable mission: Persuade NASA to send a probe to Pluto. At the time, even most astronomers weren't interested in this weird, tiny orb on the fringe of the solar system. "I was skeptical," says Fran Bagenal, then a graduate student at MIT, who was present at the meal. "Sending a mission to Pluto seemed pretty uninteresting at the time."
While Bagenal picked at her pasta, Stern waxed on about Pluto's charms. He explained his research, analyzing how the solar wind—the continuous flow of particles exhaled by the sun—blows gases from Pluto's surface like seeds from a dandelion. "I always liked to study things that were somewhat offbeat," Stern says. Pluto definitely fits—a world smaller than Earth's moon, stuck in an oval orbit tilted at a rakish angle. Stern was fascinated that Pluto in many ways resembles an overgrown comet more than an undersized planet. Its surface is covered with frozen gases that evaporate and form an atmosphere when its orbit approaches the sun. Its gravity is so weak that much of that atmosphere streams off into space, like the tail of a comet. In the 4.5-billion-year history of the solar system, whole mountain ranges and craters on Pluto's surface have simply vaporized.
Stern pointed out that every other planet in the solar system had been visited by a probe or was about to be. Each mission yielded astonishing revelations: Venus is a hellish inferno, Mars is dotted with craters and crossed with ancient channels, Jupiter is surrounded by moons of fire and ice. The more Bagenal listened, the more interested she found herself becoming: "You begin to get curious about this little thing at the edge of the solar system."
It soon became clear that Stern was prescient. Just three years after he gave his pitch in Baltimore, David Jewitt and Jane Luu of the University of Hawaii discovered QB1, a distant planetoid that resembled a smaller version of Pluto.
