There are at least 100 billion brown dwarfs and rogue planets in our galaxy. Several theories related to processes of their formation have been proposed, and could all as well be at work, but their relative importance is not known, and is expected to vary with mass and environment. Knowledge of the dominant mechanism of brown dwarf formation is one of the crucial missing pieces in our understanding of how both stars and planets come to existence. To get there, we need to study their statistical population properties, together with individual substellar object characteristics. This is best done in the places of their birth: young star clusters and star-forming regions, which did not have time to undergo significant dynamical evolution. This project addresses some of the most important unanswered questions in this research area:

1. Does the efficiency of brown dwarf formation depend on the star-forming environment?
2. How common are brown dwarfs and, in particular, planetary-mass objects (free-floating objects with masses below 12 Jupiter masses) when compared to stars?
3. What is the lower-mass limit for objects that form as stars?

This project has two main aspects, and with each of them, we plunge into so far largely unexplored regimes, which are certain to provide important clues about substellar formation. In the first part, we will study brown dwarf populations in a sample of young, massive star clusters, with environmental properties significantly different from those found in the nearby star-forming regions where substellar objects have been studied so far. The main goal is to ascertain whether high stellar densities or the influence of ionization fronts of multiple massive OB stars can affect the efficiency of brown dwarf formation, as predicted by theory. In the second part, we will look for and characterize the population of planetary-mass objects in nearby star-forming regions, down to objects as light as Jupiter. The proposed project creates and explores a synergy between currently available state-of-the-art ground-based astronomical facilities (e.g., VLT, VISTA) and those that will become available shortly, such as the recently launched James Webb Space Telescope (JWST). As a result of the two approved JWST programmes designed to tackle the questions presented above, we will, for the first time, uncover the brown dwarf population in a starburst cluster and provide immediate spectroscopic information for all objects in the field of the cluster NGC 1333 down to a single Jupiter mass.