A low-eccentricity migration pathway for a 13-h-period Earth analogue in a four-planet system

It is commonly accepted that exoplanets with orbital periods shorter than 1 day, also known as ultra-short period (USP) planets, formed further out within their natal protoplanetary disk, before migrating to current-day orbits via dynamical interactions. One of the most theories suggests a violent scenario involving high-eccentricity migration followed by tidal circularization. Here, we present discovery four planet system orbiting bright (V=10.5) K6 dwarf star TOI-500. The innermost transiting, Earth-sized USP an $\sim$ 13 hours, mass 1.42 $\pm$ 0.18 M$_{\oplus}$, radius $1.166^{0.061}_{-0.058}$ R$_{\oplus}$, and mean density 4.89$^{+1.03}_{-0.88}$ gcm$^{-3}$. Via Doppler spectroscopy, discovered hosts three outer planets on nearly circular 6.6, 26.2, 61.3d minimum masses 5.03 0.41 33.12 0.88 M$_{\oplus}$ 15.05$^{+1.12}_{-1.11}$ respectively. presence both low-mass object 6.6-day orbit indicates architecture this can be explained in which started low-eccentricity orbits, then moved inwards through quasi-static secular migration. Our numerical simulations show channel bring TOI-500 b its current location 2 Gyrs, starting from initial 0.02au. first host Earth analog whose non-violent scenario.