The Occurrence Rate of Terrestrial Planets Orbiting Nearby Mid-to-late M Dwarfs

We present an analysis of a volume-complete sample of 363 mid-to-late M dwarfs within 15 pc of the Sun with masses between 0.1 and 0.3 M⊙ observed by TESS. We search the TESS 2-minute cadence light curves for transiting planets with orbital periods below 7 days and recover all 6 known planets within the sample as well as a likely planet candidate orbiting LHS 475. Each of these planets is consistent with a terrestrial composition, with planet radii ranging from 0.91 R⊕ to 1.31 R⊕. We perform a transit injection and recovery analysis to characterize the sensitivity as a function of planet radius, insolation, and orbital period. We obtain a cumulative occurrence rate of 0.61 terrestrial planets per M dwarf with radii above 0.5 R⊕ and orbital periods between 0.4-7 days. We find that for comparable insolations, planets larger than 1.5 R⊕ (sub-Neptunes and water worlds) are significantly less abundant around mid-to-late M dwarfs compared to earlier-type stars, while the occurrence rate of terrestrial planets is comparable to that of more massive M dwarfs. We estimate that overall, terrestrials outnumber sub-Neptunes around mid-to-late M dwarfs at a ratio of 14 to 1, in contrast to GK dwarfs where they are roughly equinumerous. We find evidence for a downturn in occurrence rates for planet radii below 0.9 R⊕, suggesting that Earth-sized and larger terrestrials may be more common than Mars-sized worlds. We will also summarize work to understand the duration of the active phase of these stars, which indicates that their attendant terrestrial planets experienced very high radiation and particle fluxes for 3 Gyr, sculpting or destroying their secondary atmospheres.