(PLANETQUEST) -- For the first time ever, engineers working on JPL's Planet Detection Testbed have demonstrated that they can separate light as faint as that from a distant Earth-like planet from the blinding glare of its parent star. This breakthrough represents a major step toward the ultimate goal of the Terrestrial Planet Finder missions: observing habitable planets around nearby stars.

"The challenge in detecting an Earth-like planet is that the planet is a million times fainter than the host star when viewed in infrared light," said Dan Coulter, project manager for the Terrestrial Planet Finder Interferometer (TPF-I). "By simulating these conditions on the testbed, we've shown that the flight instrument has the sensitivity needed to suppress the light from the central star, and to observe a planet in the habitable zone." The habitable zone is the region around the system's star where the temperature is right to sustain liquid water, considered an essential ingredient for life.

The Planet Detection Testbed works by suppressing the light from the star, while allowing the planet's light to pass through and reach the detector, said Stefan Martin, the testbed lead engineer.

TPF-I will work in concert with the Terrestrial Planet Coronagraph to provide comprehensive portraits of neighboring planetary systems. Both missions are envisioned to launch within the next 10-20 years.

Sifting for planetary gold

The Planet Detection Testbed consists of a long, enclosed table bristling with dozens of precision optical components. The table is divided into two sections, the first of which houses a simulated star and planet. Their light is mixed together, then split into four beams, representing the four TPF-I collector telescopes, and fed into the other section of the table, which represents the TPF-I beam combiner flight instrument. Here, the light is combined and manipulated, and the starlight is sifted from the planet light. This situation is analogous to miners panning for scarce flakes of gold: There is only one planetary infrared photon, or particle of light, per every 1,000,000 infrared photons of starlight.

The testbed simulates the configuration of the TPF-I spacecraft, which will consist of four separated telescopes. Each telescope will collect light from a single source and steer it into a fifth spacecraft, the combiner, which does the work of suppressing the starlight and detecting the planet.

The experiment represents the first-ever demonstration of simulated planet detection using a four-beam nulling instrument, Coulter said. The breakthrough coincides with the recent success of NASA's Keck Interferometer project, which has obtained 100-to-1 suppression of starlight light from real stars observed through the Earth's atmosphere. (See related article: NASA takes giant leap toward finding Earthlike planets.)

Written by Randal Jackson/PlanetQuest