By Ron Cowen
Planet hunters Geoffrey W. Marcy and R. Paul Butler have become frequent visitors to a telescope atop Hawaii’s Mauna Kea. They come to search for alien worlds but often feel like they’ve landed on one. Rising 14,000 feet above the palm trees and lush vegetation, the windswept summit of this extinct volcano is nearly as pockmarked as the moon and as strewn with reddish rocks as Mars.
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From this desolate perch, the astronomers use the Keck I Telescope to track the motion of several hundred nearby stars. A telltale stellar wobble betrays the tug of an unseen planet. That wobble shows up as a Doppler shift, pushing the wavelength of starlight alternately toward the bluer and redder end of the spectrum as the star moves toward and away from Earth.