The CHEOPS project aims at constructing a 2^nd generation instrument for one of ESO's VLTs for direct detection of extrasolar giant planets. The phase-A feasibility study of this project ended on November 2 2004. For the extraordinarily demanding task of overcoming a contrast of at least 18 magnitudes across a separation of half a second of arc, the instrument requires

XAO

A new, adaptive optics system of extremely high order to provide the required image quality.

Contrast Enhancement

The contrast between a star and an accompanying planet is too large for direct imaging with even the most sophisticated AO system. CHEOPS will enhance the achievable contrast by two differential imagers, a polarimetric one and a spectroscopic one.

Detailed Knowledge on Targets

To optimize the chances of detection using the two differential images, detailed knowledge on the properties of planetary atmospheres - of both young and warm, and of mature planets like our own Jupiter is required. Spectra of model atmospheres and models on polarization properties have to be developed and verified. All states of planetary development and also of the central stars need to be well known.

New Methods of Observation

The number of candidates is limited to a few hundred targets due to distance and guide star brightness limitations. On the other hand the demanding XAO system will only be able to deliver its top performance in the best (~30%) seeing conditions. This requires a detailed planning scheme to execute the survey for nearby exoplanets.