Using Laser Combs to Search for Earth-like Planets

8. April 2008

Posted by Christina Folz, OPN Managing Editor

This week’s issue of Nature highlights the newest adaptation of the optical frequency comb: an “astro-comb” that astronomers can use to scour the skies for other Earth-like planets. Current methods for detecting planets orbiting distant stars are only capable of finding large planets that have at least five times the mass of the Earth, according to a press release from the Harvard-Smithsonian Center for Astrophysics (CfA).

In order to detect a planet, astronomers typically gauge its effect on the star around which it is orbiting. Using spectrography, they measure how much the star “wobbles”—a phenomenon that is caused by the gravitational pull of the planet on the star; it is a function of the planet’s mass as well as its distance from the star. Because large planets cause the most “wobble,” they are the easiest to find. In addition, planets with tight orbits around their star are easier to detect than those with wide trajectories.

The new astro-comb, which was tested by Chih-Hao Li and his colleagues from the CfA, uses ultrashort, femtosecond pulses of laser light, linked to an atomic clock, to provide an ultra-precise standard against which light from a star can be measured.  The adaptation of the optical frequency comb technique is expected to increase the resolution of the current tools by about 100 times, allowing for the detection of smaller planetary masses. According to the press release, a prototype astro-comb will be tested this summer at CfA’s Mount Hopkins Observatory in Arizona, and may be ready to use for a project in the Canary Islands by 2010.

Optical frequency combs revolutionized high-precision optical metrology by enabling scientists to accurately measure much higher frequencies of light than was ever before possible with a single tool. It is this advance for which OSA Honorary Member John L. Hall shared the 2005 Nobel Prize in Physics (with Theodor Hänsch and Roy Glauber). Hall describes his work—and its myriad exciting applications—in this month’s Scientific American magazine.  

2008-04 April, Astrophysics, Lasers , , ,