Comparison Between Extrasolar Planets and Low-Mass Secondaries
  This paper compares the statistical features of the sample of discovered extrasolar planets with those of the secondaries in nearby spectroscopic binaries, in order to enable us to distinguish between the two populations. Based on 32 planet candidates discovered until March 2000, we find that their eccentricity and period distribution are surprisingly similar to those of the binary population, while their mass distribution is remarkably different. The mass distributions definitely support the idea of two distinct populations, suggesting the planet candidates are indeed extrasolar planets. The transition between the two populations probably occurs at 10--30 Jupiter masses. We point out a possible negative correlation between the orbital period of the planets and the metallicity of their parent stars, which holds only for periods less than about 100 days. These short-period systems are characterized by circular or almost circular orbits. 
T. Mazeh, S. Zucker