Four hundred years ago, Galileo Galilei changed the world by
peering through a 3-foot-long telescope and spying the moons of
Jupiter. Today, the world — or, more accurately, our collection
of worlds — is on the brink of a change that could be just as
dramatic. Over the next five years, giant telescopes and far-
seeing space probes will revolutionize the way we think of
stars, planets and the other denizens of planetary systems,
including our own. One of the planetary pioneers is NASA's Wide-
Field Infrared Survey Explorer, launching next week from
Vandenberg Air Force Base in California. WISE is designed to
look for objects too dim and distant to be noticed by past
probes. By mid-2011, the polar-orbiting satellite should detect
around 100,000 previously unseen asteroids. Even more
intriguingly, the satellite has a chance of spotting a brown-
dwarf star or a new planet on the outskirts of the solar system.
"There is still the possibility of a large planet in the outer
solar system, according to some experts," the