Detecting Extra-Solar Planets via Microlensing at High Magnification
  Extra-solar planets can be efficiently detected in gravitational microlensing events of high magnification. High accuracy photometry is required over a short, well-defined time interval only, of order 10-30 hours. Most planets orbiting the lens star are evidenced by perturbations of the microlensing light curve in this time. 
Nicholas J. Rattenbury, Ian A. Bond, Jovan Skuljan, Phil Yock