First Direct Identification of a Multi-Star Microlens System Hosting a Planet

Gravitational microlensing produced its first exoplanet discoveries nearly 25 years ago. Because the lens and source systems separate on the sky over time due to their relative proper motion, they can eventually be resolved, allowing astronomers to study light coming directly from the lenses and place tight constraints on the physical properties of the planetary systems.

In this work, researchers analyzed high angular resolution images of the microlensing target OGLE-2006-BLG-284 using Keck adaptive optics and Hubble Space Telescope data taken more than 15 years after the event. They clearly detect the lens system and measure its motion across the Keck and HST epochs, obtaining a lens-source relative proper motion of 5.80 ± 0.15 mas yr^-1.

Combining the light curve parameters with the host star(s) brightnesses in the V, I, and K passbands gives primary and secondary host star masses of 0.43 ± 0.05 and 0.12 ± 0.02 solar masses, respectively, and a planetary companion mass of 165 +40/-33 Earth masses. The team cannot yet determine whether the planet orbits one or both stars in the system, but the analysis motivates next-generation high-precision radial velocity measurements that could distinguish these two possibilities. This is the first direct detection of flux coming from a two-star microlensing system that hosts a planet.