By Ron Cowen
For years, planet hunters have been preoccupied with hot Jupiters—giant, gaseous planets that tightly hug their sunlike parent stars. These massive, close-in planets, not yet directly seen, are the easiest to find because they induce the largest wobble in the motion of the stars they orbit. But now astronomers are following a rockier road—seeking rocky, icy planets only a few times as massive as Earth. Soon, astronomers predict, they will discover an Earth-sized planet that orbits within the habitable zone of its parent star. And if David Charbonneau has any say about it, that historic find will come from eight tiny telescopes his team has just finished assembling at the Fred Lawrence Whipple Observatory on MountHopkins in Arizona.
The telescopes, each only 40 centimeters in diameter, are designed to scan the 2,000 closest small, low-mass stars in the northern skies. The telescopes will look for signs that an orbiting planet periodically passes between the star and Earth, blocking a tiny but detectable amount of starlight every pass, or transit.
Nine years ago, Charbonneau, now at the Harvard-SmithsonianCenter for Astrophysics in Cambridge, Mass., and his then adviser, Tim Brown of the NationalCenter for Atmospheric Research’s High Altitude Observatory in Boulder, Colo., pioneered the transit method of hunting planets. The technique offers a key advantage over the wobble method, which reveals both transiting and nontransiting planets but provides only their minimum mass and the time it takes to orbit.