The size distribution of the cold classical TNOs, which can be inferred from their observed magnitude distributions, is crucial for testing theoretical models of planet formation because it reflects the outcomes of accretion, collisional processes, and dynamical evolution over the history of the Solar System. Therefore, comparing the observed size distribution with those predicted by models helps to constrain the proposed physical processes and underlying initial conditions that shaped the current Solar System. However, current streaming instability (SI) simulations have yet to completely reproduce the observed size distribution of the planetesimals primarily because of the low number statistics for smaller TNOs ( km). The relative faintness and distance of TNOs limits ground-based searches to only about magnitude. This results in increasing uncertainty in the fainter end of the size distribution and requires a more thorough planetesimal modeling.
In this talk, we present preliminary results from our pencil beam survey that utilized JWST to search and characterize ultra-faint TNOs to further constrain SI-driven models. Our JWST cycle 1 program #1568 is a 3-epoch survey that observed 0.05 deg of the sky with NIRCam short- and long-wavelength filters at 13h RA, Dec. With the sensitivity of this survey, we expect to detect and characterize TNOs as faint as mag and as small as ~5 km in diameter to explore never-before probed regions of the TNO size distribution. This is the deepest Solar System survey to date, with at least a visible magnitude deeper than the landmark survey by Bernstein et al., (2004).