Microlensing search for extrasolar planets: observational strategy, discoveries and implications

TL;DR

Microlensing is an effective method for detecting exoplanets, with recent discoveries including Earth-mass planets, and ongoing observations aim to estimate the abundance of such planets in our galaxy.

Contribution

This paper reviews the observational strategies, recent discoveries, and implications of microlensing searches for extrasolar planets, highlighting new detections and efficiency analyses.

Findings

Four exoplanets detected via microlensing, including a ~5.5 M_earth planet.

Recent observations have doubled the number of planetary candidates.

Detection efficiency diagrams enable estimation of galactic planet abundance.

Abstract

Microlensing has proven to be a valuable tool to search for extrasolar planets of Jovian- to Super-Earth-mass planets at orbits of a few AU. Since planetary signals are of very short duration, an intense and continuous monitoring is required. This is achieved by ground-based networks of telescopes (PLANET/RoboNET, microFUN) following up targets, which are identified as microlensing events by single dedicated telescopes (OGLE, MOA). Microlensing has led to four already published detections of extrasolar planets, one of them being OGLE-2005-BLG-390Lb, a planet of only ~5.5 M_earth orbiting its M-dwarf host star at ~2.6 AU. Very recent observations (May--September 2007) provided more planetary candidates, still under study, that will double the number of detections. For non-planetary microlensing events observed from 1995 to 2006 we compute detection efficiency diagrams, which can then be used to derive an estimate of the Galactic abundance of cool planets in the mass regime from Jupiters to Sub-Neptunes.