  We report the discovery of a cold planet with a very low planet/host mass
ratio of $q=(4.09\pm0.27) \times 10^{-5}$, which is similar to the ratio of
Uranus/Sun ($q=4.37 \times 10^{-5}$) in the Solar system. The Bayesian
estimates for the host mass, planet mass, system distance, and planet-host
projected separation are $M_{\rm host}=0.76\pm 0.40 M_\odot$, $M_{\rm
planet}=10.3\pm 5.5 M_\oplus$, $D_{\rm L} = 3.3\pm1.3\,{\rm kpc}$, and $a_\perp
= 3.3\pm 1.4\,{\rm au}$, respectively. The consistency of the color and
brightness expected from the estimated lens mass and distance with those of the
blend suggests the possibility that the most blended light comes from the
planet host, and this hypothesis can be established if high resolution images
are taken during the next (2020) bulge season. We discuss the importance of
conducting optimized photometry and aggressive follow-up observations for
moderately or very high magnification events to maximize the detection rate of
planets with very low mass ratios.
