Laser To Aid Search for Other Earths

Imprecise measurement has long crippled efforts to find Earth-like planets that may represent scientists’ best hope at finding extraterrestrial life, but Harvard scientists say a new laser-based measuring tool could bring the universe into sharper focus.

The astro-comb allows astronomers to discover Earth-size planets, which are most likely to support extraterrestrial life because larger planets tend to be entirely gaseous and inhospitable to organisms like those on Earth.

The laser provides a way to measure the near-imperceptible changes in a star’s light that are induced by orbiting planets.

Planet gravity minutely affects the color of light emitted by stars they orbit by altering the star’s own movements. Such light changes—called “doppler shifts”—produce redder light when gravity nudges the star towards an observer and bluer light when gravity moves it away.

But these shifts are often too small to accurately measure.

“You could find Jupiters but you couldn’t find Earths,” said Ronald L. Walsworth, a senior physics lecturer who helped lead the project. “We had a great car but it was missing a tire.”

Calibrated to an atomic clock—“the best measuring device man has in his quiver,” according to collaborator Andrew H. Szentgyorgyi—the astro-comb’s laser emits pulses every one millionth of one billionth of a second, providing the required precision against which to measure subtle shifts in the light from stars.

“It’s like we had a ruler with only half-inches on it,” said Szentgyorgyi, an associate of the Harvard College Observatory. The astro-comb “gives you lots and lots of ticks on you ruler, it’s like having rulings of a thousandth of an inch.”

The scientists say they will test the device this summer at the Mt. Hopkins Observatory in Arizona in preparation for use as part of a joint operation by Harvard and the University of Geneva that will be based in the Canary islands.

The New Earths Initiative, to which Harvard will contribute $6.5 million of astronomical equipment, including the astro-comb, will begin scanning the skies for Earth-like planets in late 2009 or early 2010, according to Szentgyorgyi.

But while many say Earth-like planets are the most likely locations of extra-terriestial life, Szentgyorgyi did note that this belief may prove unfounded.

“It may turn out that there’s really smart pond scum that eat sulfur somewhere instead,” he chuckled. “But we really see [Earth-like planets] as the first step.”

—Staff writer Clifford M. Marks can be reached at cmarks@fas.harvard.edu.