Extending the planetary mass function to Earth mass by microlensing at moderately high magnification

A measurement by microlensing of the planetary mass function of planets with masses ranging from 5M(circle plus) to 10 M-J and orbital radii from 0.5 to 10 au was reported recently. A strategy for extending the mass range down to (1-3) M-circle plus is proposed here. This entails monitoring the peaks of a few tens of microlensing events with moderately high magnifications with 1-2 m class telescopes. Planets of a few Earth masses are found to produce deviations of similar to 5 per cent to the peaks of microlensing light curves with durations similar to(0.7-3) hr in events with magnification similar to 100 if the projected separation of the planet lies in the annular region (0.85-1.2)r(E). Similar deviations are produced by Earth mass planets in the annular region (0.95-1.05)r(E). It is possible that sub-Earths could be detected very close to the Einstein ring if they are sufficiently abundant, and also planetary systems with more than one low-mass planet.