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 5 M⊕ to 10 MJ and orbital radii from 0.5 to 10 au was reported recently. A strategy for extending the mass range down to (1–3) M⊕ 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 ∼5 per cent to the peaks of microlensing light curves with durations ∼(0.7–3) hr in events with magnification ∼100 if the projected separation of the planet lies in the annular region (0.85–1.2)rE. Similar deviations are produced by Earth mass planets in the annular region (0.95–1.05)rE. 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.