Radial velocity and photometric flux of TOI-3757

This planet was discovered around a solar-metallicity M dwarf, using Transiting Exoplanet Survey Satellite photometry and confirmed with precise radial velocities from the Habitable-zone Planet Finder (HPF) and NEID. With a planetary radius of 12.0_-0.5_^+0.4^R{Earth} and mass of 85.3_-8.7_^+8.8^M{Earth}, not only does this object add to the small sample of gas giants (~10) around M dwarfs, but also its low density ({rho}=0.27_-0.04_^+0.05^g/cm^3^) provides an opportunity to test theories of planet formation.

We present two hypotheses to explain its low density; first, we posit that the low metallicity of its stellar host (~0.3dex lower than the median metallicity of M dwarfs hosting gas giants) could have played a role in the delayed formation of a solid core massive enough to initiate runaway accretion. Second, using the eccentricity estimate of 0.14{+/-}0.06, we determine it is also plausible for tidal heating to at least partially be responsible for inflating the radius of TOI-3757b.