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Description
In order to exhume the buried signatures of "missing planetary caustics" in Korea Microlensing Telescope Network (KMTNet) data, we conducted a systematic anomaly search of the residuals from point-source point-lens fits, based on a modified version of the KMTNet EventFinder algorithm. This search revealed the lowest-mass-ratio planetary caustic to date in the microlensing event OGLE-2019-BLG-1053, for which the planetary signal had not been noticed before. The planetary system has a planet-host mass ratio of q=(1.25{+/-}0.13)x10^-5^. A Bayesian analysis yielded estimates of the mass of the host star, M_host_=0.61_-0.24_^+0.29^M{sun}, the mass of its planet, M_planet_=2.48_-0.98_^+1.19^M{Earth}, the projected planet-host separation, a_perp_=3.4_-0.5_^+0.5^au, and the lens distance, D_L_=6.8_-0.9_^+0.6^kpc. The discovery of this very-low-mass-ratio planet illustrates the utility of our method and opens a new window for a large and homogeneous sample to study the microlensing planet-host mass ratio function down to q~10^-5^.
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