That's all changed in the past few years, and the plenitude of
possible worlds to explore was confirmed Wednesday when a
California Institute of Technology team reported there are
billions and billions of planets, just within this galaxy.
They're known as exoplanets, and the recent spate of discoveries
has changed astronomers' beliefs about the nature of planetary
systems. Rocky, Earth-sized planets very close to their star are
now considered the most common kind in the universe. "If you
look up at the night sky, probably every star, statistically
speaking, has a planet or two," said John Johnson, who leads
Caltech's planet-hunting Exolab. "That is a big new discovery
that's ushered in this new era of exoplanets. It was charging
forward before that, but now it's almost overwhelming." Johnson
led the study that determined there are at least 100 million
planets in the Milky Way, based on the characteristics of a star
named Kepler-32. There are five planets orbiting the star, and
all of them are visible because