Systematic KMTNet Planetary Anomaly Search. I. OGLE-2019-BLG-1053Lb, a Buried Terrestrial Planet

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) × 10 −5 . A Bayesian analysis yielded estimates of the mass of the host star, M host = 0.61 − 0.24 + 0.29 M ⊙ , the mass of its planet, M planet = 2.48 − 0.98 + 1.19 M ⊕ , the projected planet–host separation, a ⊥ = 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 .