Using TESS to Unearth the Frequency of Habitable Zone Earth-size Planets

While Kepler discovered a large number of exoplanets close to their star, the lower detectability toward small planet radii and large orbital periods resulted in the detection of just one Earth-size planet in the habitable zone of a solar analogue. Hence, determining the frequency of habitable zone Earth-size planets, hereafter EtaEarth, requires extrapolations based on the more abundant population of close-in, small planets. However, it is known that this population is contaminated by stripped cores of once sub-Neptune planets. Here, we show that when considering only planets beyond 30 days, where stripping mechanisms become inefficient, the value of EtaEarth drops from 40% to ~5-10%. Thus, quantifying the contamination of sub-Neptunes to the small, close-in planets becomes crucial to obtain a more reliable EtaEarth estimate. One way to quantify this contamination is by measuring the occurrence of primordial sub-Neptunes in young clusters (< 1 Gyr), before their envelope is stripped away. We will present our ongoing effort with TESS to de-contaminate the short-period small planet population from photoevaporated mini-Neptunes and thus provide more reliable estimates of EtaEarth.