Orbital properties of extra-solar planets are briefly recalled and compared with equivalent features of stellar binaries. Similarities and differences are discussed. Among the more than 115 extra-solar planets discovered to date, 19 are orbiting a component of a binary system. We discuss the properties of this subsample and compare them with the equivalent characteristics of planets around single stars. Differences in the mass-period-eccentricity distributions are observed: exoplanets with m2 sin i > 2 MJup and P≤ 40-100 days are in binaries and present low eccentricities. In the context of the migration scenario, these characteristics are tentatively explained in the light of recent simulations of planet-disk interactions showing an increased accretion and migration rates of planets in case an additional perturbing close stellar companion is present in the system. Finally, different observational approaches to find planets in long-period spectroscopic binaries aiming to improve the still poor available statistics are presented. An important result is the detection of a planetary companion in the HD 41004 triple system.

The properties of planets orbiting a component of a binary or multiple-star system appear different from the ones of planets orbiting isolated stars (Udry et al. 2004). The effect of binarity has, however, still to be better characterized and quantified. In this contribution, we describe a VLT/NACO adaptive optics survey aimed at pointing out the potential effect of stellar duplicity on planet formation and evolution, by comparing the faint-companion statistics of similarly selected subsamples of stars with and without planets. The statistical results of the survey will allow us to possiblydiscriminate between the proposed models of planetary formation (accretion or disk instability), some of them predicting different influences of stellar duplicity. Preliminary results are already very interesting: 20 ± 7% of the “single” stars present companions within ~10″, whereas only 3 ± 3% equivalent companions are found close to stars hosting planets.