INTRODUCTION The statistical distribution of the masses of planets about
The nearly circular and coplanar orbits of the planets stars between the Sun and the center of the Galaxy is conaround the Sun point to the formation of these planets from strained to within a factor of 3 by an intensive search for planets a highly dissipative disk of gas and dust. The inevitability of
microlensing events. Projected separations in terms of the lens Einstein ring radius yield a rough estimate of the the natural formation of such a disk during the gravitadistribution of planetary semimajor axes with planetary mass. tional collapse of a rotating molecular cloud to form a The search consists of following ongoing stellar microlensing star and the observational confirmation that essentially all events involving sources in the center of the Galaxy lensed by recently formed stars possess such a disk (e.g., Strom et intervening stars with high-time-resolution, 1% photometry in al. 1995) have led most to believe that planetary systems two colors in an attempt to catch any short-time-scale planetary are a common result of the star formation process and perturbations of the otherwise smooth lightcurve. It is assumed therefore must be ubiquitous in the galaxy. The recent that 3000 events are followed over an 8-year period, but with discovery of planetary sized bodies around several nearby half of the lenses, those that are members of binary systems, stars (Mayor and Queloz 1995, Marcy and Butler 1996, devoid of planets. The remaining 1500 lenses have Solar