The Importance of Jupiters in a Microlensing Search for Planets

The recently discovered planetary mass bodies around several nearby stars have revealed systems very much unlike our own with the possible exception of Lalande 21185, which seems to have a planet of 1.4 +/- 0.2 Jupiter masses (m(J)) at 7.5 +/- 0.5 AU with a period of 32 +/- 4 years in a low eccentricity orbit. The star 47 UMa has a planet of minimum mass of 2.4 m(J) in nearly circular orbit at 2.1 AU, 70 Vir has a companion more massive than 6.6 m(J) a with semimajor axis of about 0.43 AU and eccentricity of about 0.4. Although there are severe observational selection effects constraining the properties of these detected planetary mass bodies, it is striking that almost 3 percent of the stars monitored in radial velocity surveys are found to have giant planets at distances much closer to their stars than where they could have formed by accretion of solid planetesimals and subsequent capture of large gaseous envelopes.