Collaborative Research: Tracing the Origins of Free-Floating Planets Through Chemical Composition

Free-floating planets with masses of 3–30 times the mass of Jupiter sit at the intersection of star-like and planet-like formation pathways, yet the relative contributions of these formation channels remain unknown. Traditional approaches rely on extending the measurements of stellar initial mass functions (IMFs, the distribution of stellar masses when stars first form out of a molecular cloud) into the planetary-mass regime in nearby star-forming regions, but these approaches are challenged by the intrinsic faintness of these planets, contamination among photometric candidates, and the small number of spectroscopically confirmed members. Researchers from the University of Rochester and University of California, Santa Cruz will establish a new framework for tracing the origins of free-floating planets using their chemical compositions rather than number counts. By mapping their carbon-to-oxygen ratios and metallicities as a function of mass, the team will determine whether free-floating planets form exclusively through star-like processes, or through a combination of star-like and planet-like channels marked by a transition mass. The program will contribute to strengthening STEM education and workforce development by establishing a Research Computing and Artificial Intelligence (AI) Bootcamp at the University of Rochester. The research program will focus on the Upper Scorpius star-forming region and analyze high-quality 0.8–2.5 μm spectra for a carefully-selected sample of 42 spectroscopically confirmed free-floating planets. The proposed analysis leverages this existing population of spectroscopically confirmed free-floating planets, which is too small for IMF studies but ideally suited for our hypothesis-testing framework for tracing their origins. The project aims to create the largest publicly available, high-quality spectroscopic library of free-floating planets in Upper Scorpius; uniformly measure C/O and [Fe/H] by combining atmospheric retrievals and grid-based forward-modeling analyses, the two major techniques for characterizing exoplanets and brown dwarfs; and test the formation hypotheses of free-floating planets by quantifying how their chemical compositions (C/O, [Fe/H]) vary with mass. Beyond revealing formation pathways, the program will also deliver high-precision atmospheric characterization of young free-floating planets. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.