NASA is gearing up for a space race that's expected to point to the first truly Earthlike worlds beyond our solar system - and, like the race to put the first human on the moon, this marathon will take several years to run.

The roots of the race go back more than a decade, as astrophysicist Alan Boss explains in his new book, "The Crowded Universe: The Search for Living Planets." That's when pioneers in the planet-hunting field started detecting worlds around suns beyond our own.

The techniques used back then couldn't find other Earths in planetary systems like our own. The first method, pioneered by Polish astronomer Alexander Wolszczan at the Arecibo Observatory in 1991, could detect Earth-scale planets (and perhaps even the first known extrasolar dwarf planet) around radio pulsars - but those planets were thought to be burned-out cinders and not Earthlike at all.

In 1995, astronomers began reporting the detection of Jupiter-scale planets around normal stars, by precisely measuring the gravitational wobble those planets induce in the stars themselves. (Our interactive tutorial explains how it's done.) As the years have gone by, planet-hunters have gotten smarter about using that "Doppler wobble" technique, and they've also trained sensitive telescopes on faraway stars to measure the slight dimming in their light as alien planets make their transits over the stars' disks.

This transit method takes center stage in the next phase of the planet-hunting space race: The European Space Agency's Corot satellite, which was launched a little more than two years ago, has a head start. Just this month, members of the Corot science team announced the discovery of a "hot super-Earth" that is less than twice Earth's size.

Next month, NASA picks up the pace with the launch of its Kepler satellite, equipped with a planet-seeking telescope that has some advantages over Corot. Astronomers expect Kepler to turn up some true Earthlike planets, in Earthlike orbits, around sunlike stars.

"If Kepler comes up empty-handed - boy, it'll turn out to be virtual harakiri," Boss, a member of the Kepler science team, told me earlier this month. "But there's little chance of that."

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