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<-   The host stars  
figures/distances.png
Histogram of the distances of the stars around which some planets have been discovered in July 2007. Most of the stars are located between 10 and 130 parsecs.
Copyright : Paris Observatory / Jean Schneider et al.

The distance of these stars from the Earth greatly varies according to the detection technique used.

  • One has recently been able to detect a few exoplanets in the close solar neighbourhood (at a distance of around a hundred light-years.) with direct imaging methods. However, imaging of exoplanets is very difficult and one only begins to make the first discoveries using this method.

  • With the radial velocity method, which has provided the majority of the distance measurements of host stars, the distance of the host stars from Earth is typically about one hundred light-years. Note that all these stars belong to our Galaxy Galaxy, whose diameter is approximately 100 000 light-years.

  • With other techniques, the distance of the host stars can be much greater, as far as about 6000 light-years (to date) for the transit photometry method, and even 12 000 light-years for the pulsar chronometry technique. One now begins also to detect the first candidates for very remote exoplanets, up to about 21 000 light-years, with the gravitational lensing method.

    Today, only a small part of our Galaxy has been investigated. Exoplanets cannot be detected around stars from other galaxies, except, maybe, with the gravitational lensing method.