He and his team, in 2007, discovered a possibly terrestrial planet in the habitable zone of the Gliese 581 planetary system, approximately 20 light years away in the constellation Libra.

Later, Udry returned to Geneva, and worked with Michel Mayor, the discoverer of 51 Pegasi b, the first extrasolar planet found revolving around a normal star.

His current work chiefly concerns the search for extra-solar planets by analyzing variations in the radial velocities of stars.

Udry described a new instrument known as the Echelle Spectrography for Rocky Exoplanet and Stable Spectroscopic Observations, dubbed ESPRESSO, might allow astronomers to detect Earth-like planets within five to ten years from 2010.

[5] An upgraded HARPS, of which Udry lead the observational team, found evidence that Gliese 581d might be more habitable (rather than c or g), and also detected another promising candidate: HD 85512 b.