Microlensing detections of cool planets are important for the construction of an unbiased sample to estimate the frequency of planets beyond the snow line , which is where giant planets are thought to form according to the core accretion theory of planet formation .
In this paper , we report the discovery of a giant planet detected from the analysis of the light curve of a high-magnification microlensing event MOA 2010-BLG-477 .
The measured planet-star mass ratio is q = ( 2.181 \pm 0.004 ) \times 10 ^ { -3 } and the projected separation is s = 1.1228 \pm 0.0006 in units of the Einstein radius .
The angular Einstein radius is unusually large \theta _ { E } = 1.38 \pm 0.11 mas .
Combining this measurement with constraints on the “ microlens parallax ” and the lens flux , we can only limit the host mass to the range 0.13 < M / M _ { \odot } < 1.0 .
In this particular case , the strong degeneracy between microlensing parallax and planet orbital motion prevents us from measuring more accurate host and planet masses .
However , we find that adding Bayesian priors from two effects ( Galactic model and Keplerian orbit ) each independently favors the upper end of this mass range , yielding star and planet masses of M _ { * } = 0.67 ^ { +0.33 } _ { -0.13 } M _ { \odot } and m _ { p } = 1.5 ^ { +0.8 } _ { -0.3 } M _ { JUP } at a distance of D = 2.3 \pm 0.6 kpc , and with a semi-major axis of a = 2 ^ { +3 } _ { -1 } AU .
Finally , we show that the lens mass can be determined from future high-resolution near-IR adaptive optics observations independently from two effects , photometric and astrometric .