Exoplanet searches with gravitational microlensing

Different regimes of gravitational lensing depend on lens masses and roughly correspond to angular dis- tance between images. If a gravitational lens has a typical stellar mass, this regime is named microlens- ing because the typical angular distance between im- ages is about microarcseconds in the case for sources and lenses at cosmological distances. The angular dis- tance depends on as a squared root of lens mass and therefore, for Earth-like planet mass lens (10−6 M ), such a regime is called nanolensing. So, one can name searches for exoplanets with gravitational lens method as gravitational nanolensing. There are differ- ent methods for finding exoplanets such as radial spec- tral shifts, astrometrical measurements, transits, tim- ing etc. Gravitational microlensing (including pixel- lensing) is among the most promising techniques with the potentiality of detecting Earth-like planets at dis- tances about a few astronomical units from their host stars.