Light-detection method translates to precision for detection of extrasolar planets

An invention by researchers at the Harvard-Smithsonian Center for Astrophysics (Cambridge, MA), who will present their findings at the 2009 Conference on Lasers and Electro Optics/International Quantum Electronics Conference (CLEO/IQEC, May 31 to June 5, Baltimore, MD) lets astronomers more precisely determine size and movement of planets in solar systems other than our own. The approach promises to reveal Earth-like planets orbiting distant stars.

In most cases, extrasolar planets can't be seen directly, but spectroscopy can reveal their influence and their component chemistry, plus how fast the star is moving away from or toward Earth. Though the planet might weigh millions of times less than the star, the gravity interaction between star and planet will impose a slight jerking motion on the star, which causes the star to move slightly toward or away from Earth in a way that depends on the planet's mass and its nearness to the star. The better the spectroscopy used in this whole process, the better will be the identification of the planet in the first place and the better will be the determination of planetary properties.

Current spectroscopy techniques can determine star movements to within a few meters per second. In tests, the Harvard researchers are now able to calculate star velocity shifts of less than 1 m/sec, allowing them to more accurately pinpoint the planet's location.

Smithsonian researcher David Phillips says that he and his colleagues expect to reach a velocity resolution of 60 cm/sec, and maybe even 1 cm/sec, which when applied to the activities of large telescopes presently under construction, would open new possibilities in astronomy and astrophysics, including simpler detection of more Earth-like planets.

With this new approach, Harvard astronomers achieve their great improvement using a frequency comb as the basis for their "astro-comb" invention. A special laser system is used to emit light not at a single energy but a series of energies (or frequencies), evenly spaced across a wide range of values. The energy of these comb-like laser pulses is known so well that they can be used to calibrate the energy of light coming in from the distant star. In effect, the frequency comb approach sharpens the spectroscopy process.

The astro-comb method has been tried out on a medium-sized telescope in Arizona and will soon be installed on the much larger William Herschel Telescope, which resides on a mountaintop in the Canary Islands.

Presentation CMII1, "Femtosecond Laser Frequency Comb for Precision Astrophysical Spectroscopy," by Chih-Hao Li et al, will take place at 3:45 p.m. on Monday, June 1.

Find details on the astro-comb at the Harvard-Smithsonian Center for Astrophysics site. And learn more about CLEO/IQEC 2009 at the conference site.