TESS discovery of a super-Earth and three sub-Neptunes hosted by the bright, Sun-like star HD 108236

We report the discovery and validation of four extrasolar planets hosted by the nearby, bright, Sun-like (G3V) star HD~108236 using data from the Transiting Exoplanet Survey Satellite (TESS). We present transit photometry, reconnaissance and precise Doppler spectroscopy as well as high-resolution imaging, to validate the planetary nature of the objects transiting HD~108236, also known as the TESS Object of Interest (TOI) 1233. The innermost planet is a possibly-rocky super-Earth with a period of 3.79523^(+0.00047)_(−0.00044) days and has a radius of 1.586 ± 0.098 R_⊕. The outer planets are sub-Neptunes, with potential gaseous envelopes, having radii of 2.068^(+0.10)_(−0.091) R_⊕, 2.72 ± 0.11 R_⊕, and 3.12^(+0.13)_(−0.12) R_⊕ and periods of 6.20370^(+0.00064)_(−0.00052) days, 14.17555^(+0.00099)_(−0.0011) days, and 19.5917^(+0.0022)_(−0.0020_ days, respectively. With V and Ks magnitudes of 9.2 and 7.6, respectively, the bright host star makes the transiting planets favorable targets for mass measurements and, potentially, for atmospheric characterization via transmission spectroscopy. HD~108236 is the brightest Sun-like star in the visual (V) band known to host four or more transiting exoplanets. The discovered planets span a broad range of planetary radii and equilibrium temperatures, and share a common history of insolation from a Sun-like star (R_★ = 0.888 ± 0.017 R_⊙, T_(eff) = 5730 ± 50 K), making HD 108236 an exciting, opportune cosmic laboratory for testing models of planet formation and evolution.