Radial velocity follow up of TOI-1842

We report the detection and confirmation of TOI-1842b, a warm Saturn identified by TESS and confirmed with ground-based observations from Minerva-Australis, NRES, and the Las Cumbres Observatory Global Telescope. This planet has a radius of 1.04_-0.05_^+0.06^R_J_, a mass of 0.214_-0.038_^+0.040^M_J_, an orbital period of 9.5739_-0.0001_^+0.0002^days, and an extremely low density ({rho}=0.252{+/-}0.091g/cm^3^).

TOI-1842b has among the best known combinations of large atmospheric scale height (893km) and host-star brightness (J=8.747mag), making it an attractive target for atmospheric characterization. As the host star is beginning to evolve off the main sequence, TOI-1842b presents an excellent opportunity to test models of gas giant reinflation. The primary transit duration of only 4.3hr also makes TOI-1842b an easily-schedulable target for further ground-based atmospheric characterization.