Imagine yourself gazing at the sky on a summer night. You look in the direction of a particular star that, you have heard, has a special planet orbiting around it. Although you cannot actually see the planet—you can barely see the star itself—you know it is several times larger than Earth and, like Earth, is made mostly of rock. Quakes sometimes shake its surface, much of which is covered by oceans. Its atmosphere is not too different from the one we breathe, and its sky is swept by frequent storms and often darkened by the ash of volcanoes. But most of all, you know that scientists think it could harbor life—and that they plan to seek evidence for it.
This scenario could become reality within the next decade. Although most of the 450-odd extrasolar planets found so far are giants more similar to Jupiter, astronomers are beginning to discover some that may not be too different from Earth. And NASA’s Kepler probe, a planet hunter sent aloft last year, will discover many more.