Systematic KMTNet Planetary Anomaly Search, Paper I: OGLE-2019-BLG-1053Lb, A Buried Terrestrial Planet

In order to exhume the buried signatures of "missing planetary caustics" in the KMTNet data, we conducted a systematic anomaly search to the residuals from point-source point-lens fits, based on a modified version of the KMTNet EventFinder algorithm. This search reveals 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 \(q = (1.25 \pm 0.13) \times 10^{-5}\). A Bayesian analysis yields estimates of the mass of the host star, \(M_{\rm host} = 0.61_{-0.24}^{+0.29}~M_\odot\), the mass of its planet, \(M_{\rm planet} = 2.48_{-0.98}^{+1.19}~M_{\oplus}\), the projected planet-host separation, \(a_\perp = 3.4_{-0.5}^{+0.5}\) au, and the lens distance of \(D_{\rm L} = 6.8_{-0.9}^{+0.6}\) 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 \(q \sim 10^{-5}\).