IMAGING CIRCUMSTELLAR ENVIRONMENTS WITH A NULLING INTERFEROMETER

Extrasolar planets must be imaged directly if their nature is to be be tter understood. But this will be difficult, as the bright light from the parent star (or rather its diffracted halo in the imaging apparatu s) can easily overwhelm nearby faint sources. Bracewell has proposed(1 ) a way of selectively removing: starlight before detection, by superp osing the light from two telescopes so that the stellar wavefronts int erfere destructively. Such a 'nulling' interferometer could be used in space to search for extrasolar Earth-like planets through their therm al emission and to determine through spectroscopic analysis if they po ssess the atmospheric signatures of life(2-4). Here we report mid-infr ared observations using two co-mounted telescopes of the Multiple Mirr or Telescope that demonstrate the viability of this technique. Images of unresolved stars are seen to disappear almost completely, while Lig ht from a nearby source as dose as 0.2 arcsec remains, as shown by ima ges of Betelgeuse. With this star cancelled, there remains the thermal image of its surrounding, small dust nebula. In the future, larger gr ound-based interferometers that correct for atmospheric distortions (u sing adaptive optics) should achieve better cancellation, allowing dir ect detection of warm, Jupiter-size planets and faint zodiacal dust ar ound other nearby stars(5).