An Earth-mass planet in a time of COVID-19: KMT-2020-BLG-0414Lb

We report the discovery of KMT-2020-BLG-0414Lb, with a planet-to-host mass ratio $q_2 = 0.9$--$1.2 \times 10^{-5} 3$--$4~q_{\oplus}$ at $1\sigma$, which is lowest mass-ratio microlensing planet to date. Together two other recent discoveries ($4 \lesssim q/q_\oplus 6$), it fills out previous empty sector bottom triangular $(\log s, \log q)$ diagram, where $s$ planet-host separation in units angular Einstein radius $\theta_{\rm E}$. Hence, these call into question existence, or least strength, break function that was previously suggested account for paucity very low-$q$ planets. Due extreme magnification event, $A_{\rm max}\sim 1450$ underlying single-lens its light curve revealed second companion $q_3 \sim 0.05$ and $|\log s_3| 1$, i.e., factor $\sim 10$ closer farther from host projection. The measurements microlens parallax $\pi_{\rm E}$ allow estimates host, planet, masses, $(M_1, M_2, M_3) (0.3M_{\odot}, 1.0M_{\oplus}, 17M_{J})$, projected separations, $(a_{\perp,2}, a_{\perp,3}) (1.5, 0.15~{\rm or}~15)$~au, system distance $D_{\rm L} 1$ kpc. lens could most all blended ($I 19.3$) so can be studied immediately high-resolution photometric spectroscopic observations further clarify nature system. found as part new program high-cadence follow-up high-magnification events. detection this despite considerable difficulties imposed by Covid-19 (two KMT sites OGLE were shut down), illustrates potential utility program.