Discovering planetary systems through gravitational microlenses

Planetary systems of Galactic disk stars can be detected as microlenses of stars in the Galactic bulge. Planets in a solar-like system positioned half-way to the Galactic center should leave a noticeable signature (magnification larger than 5 percent) on the light curve of a gravitationally lensed bulge star in about 20 percent of the microlensing events. This high probability results from a coincidence between Jupiter's orbital radius and the solar Einstein radius at this distance. Typical planetary signals last for about 1 day, a small fraction of the approximately 1 month duration of the entire microlensing event. Dedicated monitoring of microlensing candidates is suggested as a method to discover planetary systems in conjunction with forthcoming observations toward the Galactic bulge.