ESA Science & Technology08-Jul-2005 11:29:17

Extrasolar Planets

Nulling Interferometer

The light from individual telescopes can be combined to simulate collection by a much larger telescope. This technique is called interferometry and was pioneered using radio telescopes.

It is now being applied to optical and infrared telescopes. This method relies on the wave nature of light. A wave has peaks and troughs. Usually when combining light in an interferometer, the peaks are lined up with one another, boosting the signal. In nulling interferometry, however, the peaks are lined up with the troughs so they cancel each other out and the star disappears. Planets in orbit around the star show up, however, because they are offset from the central star and their light takes different paths through the telescope system.

Within five years, a team of astronomers from ESA and ESO will be using a nulling interferometer. The team will use the four 8-metre telescopes of ESO's Very Large Telescope and will combine the beams with GENIE (Ground-based European Nulling Interferometer Experiment). GENIE may be able to take pictures of 'hot' Jupiters but will be hampered by our planet's atmosphere.

Other ground based nulling interferometers are also being developed around the world to perfect the technique. Eventually, sophisticated flotillas of spacecraft, such as ESA's Darwin mission, will use nulling interferometry to isolate the light from Earth-like extrasolar planets.

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