Hunting for Cold Exoplanets via Microlensing

Abstract

Microlensing can detect planets at distances ranging from a few hundred parsecs all the way to the Galactic center. The maximum sensitivity is reached for systems that are located half way to the galactic center, with planets orbiting the lens star at a separation of few AUs. It is the only method currently probing exoplanets in the Earth-Saturn mass range beyond the snow line, where the core accretion theory originally predicted that most massive planets would form. Although the number of detected planets is relatively modest ($\sim 130$ planets to date) compared to that discovered by radial velocity and transit methods, microlensing probes a part of the parameter space (host separation as a function of planet mass), which is mostly not accessible in the medium term to any other technique. Microlensing has discovered the first cold super-Earth, and the first Jupiter planet orbiting a white dwarf. It also detected a number of Earth, Super-Earth, Neptune, Saturn, Jupiter, super-Jupiter orbiting main sequence stars in the mass range $0.08-1 M_\odot $. It also observed circumbinary planets, Jupiter in the habitable zone, the first exomoon candidate and free-floating planets. It has shown that having a planet is the rule for stars in our galaxy and shown that super-Earth and Neptune are more abundant than smaller mass telluric planets. Ground based microlensing will provide soon the mass function of cold planets down to few Earth Masses. The next phase, is a 450 days survey with the NASA Nancy Grace Roman Space Telescope from 2027. It will detect 3000+ planets and provide the mass function of cold planets down to the mass of Mars. If combined with the European Euclid Space mission, we will be able to probe for free-floating telluric planets and measure their masses.

Keywords

• Exoplanets
• Gravitational Lensing
• Observations
• Detection of Exoplanets
• Planetary Systems
• Micro-lensing