  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 $q \sim 10^{-5}$.
