Terrestrial Planets Vastly Outnumber Sub-Neptunes and Gas Giants Around Mid-to-Late M Dwarfs

M dwarfs are the only type of star where the presence of planets in the habitable zone can be systematically studied with currently available photometric data. Crucially, on-going observations by TESS have enabled us to search for Earth-sized and smaller planets around mid-to-late M dwarfs (stars with masses below 0.3 M_Sun), which were poorly represented in the Kepler sample due to their host stars’ low inherent luminosities. Such planets are also prime targets for transmission spectroscopy with state-of-the-art instruments. Recent analysis has determined that the population of planets around mid-to-late M dwarfs is profoundly different from that of Sun-like stars: in Ment & Charbonneau (2023), we found that warm terrestrial planets outnumber warm sub-Neptunes and gas giants at a ratio of 14:1 within the orbital period regime below 7 days (or equivalently, insolations above 4 S_Earth). We extend these results by utilizing 69 sectors of TESS photometry to search for planets with orbital periods up to 30 days, encompassing the habitable zone. We calculate planet occurrence rates as a function of orbital period, planet radius, and stellar insolation. We compare these results to previous studies of early M dwarfs and FGK dwarfs based on Kepler and K2 data. We present evidence that mid-to-late M dwarfs do not harbor more planets compared to early M dwarfs, reversing the stellar mass-dependent trend that is evident in stars with masses above 0.3 M_Sun. This finding supports results from pebble accretion simulations. We also present the terrestrial planet incidence rate as a function of planet radius down to 0.5 R_Earth, focusing specifically on the relative abundance of sub-Earth-sized planets compared to Earth-sized and larger terrestrials. We find that terrestrial planets orbiting mid-to-late M dwarfs may be preferentially Earth-sized, as opposed to substantially larger or smaller.