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Abstract A successful theory of star formation should predict the number of objects as a function of their mass produced through star-forming events. Previous studies in star-forming regions and the solar neighborhood have identified a mass function increasing from the hydrogen-burning limit down to about 10M_J. Theory predicts a limit to the fragmentation process, providing a natural turnover in the mass function down to the opacity limit of turbulent fragmentation, thought to be near 1–10M_J. Programs to date have not been sensitive enough to probe the hypothesized opacity limit of fragmentation. We present the first identification of a turnover in the initial mass function below 12M_Jwithin NGC 2024, a young star-forming region. With JWST/NIRCam deep exposures across 0.7–5μm, we identified several free-floating objects down to roughly 3M_Jwith sensitivity to 0.5M_J. We present evidence for a double power-law model increasing from about 60M_Jto roughly 12M_J, consistent with previous studies, followed by a decrease down to 0.5M_J. Our results support the predictions of star and brown dwarf formation theory, identifying the theoretical turnover in the mass function and suggesting the fundamental limit of turbulent fragmentation to be near 3M_J. 

Recent years have seen a surge of interest in the community studying the effect of ultraviolet radiation environment, predominantly set by OB stars, on protoplanetary disc evolution and planet formation. This is important because a significant fraction of planetary systems, potentially including our own, formed in close proximity to OB stars. This is a rapidly developing field, with a broad range of observations across many regions recently obtained or recently scheduled. In this paper, stimulated by a series of workshops on the topic, we take stock of the current and upcoming observations. We discuss how the community can build on this recent success with future observations to make progress in answering the big questions of the field, with the broad goal of disentangling how external photoevaporation contributes to shaping the observed (exo)planet population. Both existing and future instruments offer numerous opportunities to make progress towards this goal.