TESS Hunt for Young and Maturing Exoplanets (THYME) X: a two-planet system in the 210 Myr MELANGE-5 Association

Young (<500 Myr) planets are critical to studying how planets form and evolve. Among these young planetary systems, multi-planet configurations are particularly useful as they provide a means to control for variables within a system. Here, we report the discovery and characterization of a young planetary system, TOI-1224. We show that the planet-host resides within a young population we denote as MELANGE-5 . By employing a range of age-dating methods – isochrone fitting, lithium abundance analysis, gyrochronology, and Gaia excess variability – we estimate the age of MELANGE-5 to be 210±27 Myr. MELANGE-5 is situated in close proximity to previously identified younger (80 -110 Myr) associations, Crius 221 and Theia 424/Volans-Carina, motivating further work to map out the group boundaries. In addition to a planet candidate detected by the TESS pipeline and alerted as a TESS Object of Interest, TOI-1224 b, we identify a second planet, TOI-1224 c, using custom search tools optimized for young stars (Notch and LOCoR). We find the planets are 2.10±0.09R_⊕ and 2.88±0.10R_⊕ and orbit their host star every 4.18 and 17.95 days, respectively. With their bright (K=9.1 mag), small (R_*=0.44R_⊙), and cool (T_eff =3326K) host star, these planets represent excellent candidates for atmospheric characterization with JWST.