We used Keck adaptive optics observations to identify the first planet discovered by microlensing to lie in or near the habitable zone , i.e. , at projected separation r _ { \perp } = 1.1 \pm 0.1 AU from its M _ { L } = 0.86 \pm 0.06 M _ { \odot } host , being the highest microlensing mass definitely identified .
The planet has a mass m _ { p } = 4.8 \pm 0.3 M _ { Jup } , and could in principle have habitable moons .
This is also the first planet to be identified as being in the Galactic bulge with good confidence : D _ { L } = 7.72 \pm 0.44 kpc .
The planet/host masses and distance were previously not known , but only estimated using Bayesian priors based on a Galactic model ( Yee et al .
2012 ) .
These estimates had suggested that the planet might be a super-Jupiter orbiting an M dwarf , a very rare class of planets .
We obtained high-resolution JHK images using Keck adaptive optics to detect the lens and so test this hypothesis .
We clearly detect light from a G dwarf at the position of the event , and exclude all interpretations other than that this is the lens with high confidence ( 95 \% ) , using a new astrometric technique .
The calibrated magnitude of the planet host star is H _ { L } = 19.16 \pm 0.13 .
We infer the following probabilities for the three possible orbital configurations of the gas giant planet : 53 \% to be in the habitable zone , 35 \% to be near the habitable zone , and 12 \% to be beyond the snow line , depending on the atmospherical conditions and the uncertainties on the semimajor axis .