NASA's Kepler spacecraft, launched in 2009, is one of the finest and most prolific machines ever built for seeking out worlds orbiting distant stars. And at an estimated cost of $600 million, it had better be.

Now anyone can sift through a bit of Kepler's voluminous data, obtained as the space telescope gazes at some 150,000 stars to monitor their brightness over several years. For those stars that host planets, and for those planets whose orbits are aligned with Kepler's sight line, the spacecraft's light sensors register a dip in the star's brightness when a planet passes across the star's face, a sort of partial eclipse known as a transit.

Those data are automatically filtered to locate possible planetary transits—at last count, the spacecraft had located eight exoplanets and several hundred more candidates that await confirmation. But what if the filtering algorithms miss something interesting?

Enter Planet Hunters, a citizen-scientist-powered Web site that lets any average Joe with an Internet connection peruse Kepler light curves—measurements of a star's brightness over time—and look for the dimming signifying the possible presence of a planet. The site, which launched December 16, was created by some of the same people who produced the highly successful online galaxy-sorting project Galaxy Zoo.

The Planet Hunters interface is quite slick; the system asks users a set of simple questions about the data before them (although interpreting the data to answer those questions can be intimidating at first), and users can zoom in on promising areas of a star's light curve to try to discriminate between a transit and mere noise. But in a test drive, this reporter had a hard time locating anything that might plausibly represent a planet. Nevertheless I felt pressure to do the job well—what if some intelligent race of beings inhabiting some faraway world eludes discovery, simply because I was too lazy or too myopic to properly evaluate my serving of data? I was probably just being paranoid, but there is another, more realistic motivation for becoming an ace reader of light curves. If the Planet Hunters project turns up a new world that others missed in Kepler's data, the citizen scientist who flags its presence will be listed as a co-author on the scientific paper announcing the discovery.

Artwork credit: Haven Giguere/Yale