True abundance of Earth-mass free-floating planets

Determine the true Galactic abundance and number density of free-floating planets with masses near Earth mass (i.e., within approximately a half-decade of M⊕), so as to accurately normalize the mass function in the terrestrial-mass regime and calibrate expected microlensing event rates.

Background

In estimating the expected number of detectable microlensing events, the analysis adopts a normalization for the lens number density based on the MOA collaboration’s inferred mass function, corresponding to roughly 22 free-floating planets per star within a half-decade of Earth mass. This normalization directly sets the event-rate estimate used to assess TESS’s prospects for detecting short-timescale microlensing from terrestrial-mass lenses.

However, the authors emphasize that the true abundance of free-floating planets in this Earth-mass range is currently unknown and could be significantly higher. Since TESS is well-suited to probe short-duration events caused by low-mass lenses, establishing the correct normalization in this mass regime is essential to interpreting yields and constraining the underlying population.