Researchers at the Harvard-Smithsonian Center for Astrophysics have adapted a relatively young laser technology to discern the once undetectably faint gravitational influence a rocky, Earth-like planet revolving around a Sun-like star exerts on their home stars' light output.
If the Harvard technique holds up in use on actual telescopes, it could be "a huge breakthrough" in the search for Earth-like planets, which will help scientists "understand how our own Earth came to be" and search for life beyond our planet, says Sara Seager, a professor of earth and planetary sciences at MIT in an interview with the MIT Technology Review.
The Harvard system increases the precision of spectrographs--optics used to analyze light from distant stars--by a hundred times, and it should make it possible to detect Earth-like planets. This May, Harvard senior lecturer Ronald Walsworth and postdoctoral Chih-Hao Li (left) will be installing the system at the Multiple Mirror Telescope on Mount Hopkins, in Arizona.
To date, astronomers have discovered nearly 300 exoplanets, outside our own solar system. In March, astronomers at NASA announced that the Hubble Space Telescope had detected evidence of water and an organic molecule on a planet 63 light years away reported in the Daily Galaxy. But that planet is gaseous and awesomely hot. To date, none of the exoplanets yet found are Earth-like.
The effects of small planets like Earth on the motions of their stars are subtle, on the order of a centimeter per second, and the shifts in wavelength are correspondingly tiny. "Current techniques have reached a wall at one meter per second," says Gordon Walker, an emeritus professor of physics and astronomy at the University of British Columbia.
The fringes of light in an unmodified optical-frequency comb are too closely spaced together. To solve this problem, Walsworth and Li coupled an optical-frequency comb with a filtering chamber called a Fabry-Pérot cavity that uses a series of mirrors to cancel out most of the fringes. The resulting fringes act like a ruler for precisely identifying the wavelengths of light in a spectrograph.
"There are a bunch of people working on this, and they beat them out," Seager told MIT Technology Review of the Harvard researchers. Other groups working on the problem are starting from the top down, designing techniques that need to be combined with better telescopes and better spectrographs also currently under development. Walsworth took a simple approach to the problem. His calibration technique can be used on existing telescopes, with existing spectrographs.
Walsworth says that it will still be a few years before new Earth-like planets are detected using the new technique. His group is currently adapting the frequency-comb system for transport from Massachusetts to Arizona, where it will be used to calibrate the spectrograph at the Multiple Mirror Telescope.
In 2010, the system will be installed on a state-of-the-art spectrograph in the Canary Islands. "The ultimate goal is to find planets of Earth mass with a one-year period around a Sun-like star," says Walsworth. But he notes that the first discoveries using the new system will be rocky planets orbiting more closely to dimmer, cooler stars.
Posted by Casey Kazan.
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