Exploring free-floating planetary-mass objects with the James Webb Space Telescope

Stars and planets are fundamentally different celestial objects - in academic research as well as in our common sense understanding. While stars are hot, gaseous bodies born from giant clouds, planets are much smaller, born in orbit around stars, and potentially life-supporting. Despite these differences, there is thus far no clear delineation between stars and planets.

Nature produces a bounty of objects at masses between giant planets and low-mass stars, both in orbit around stars and free-floating in space.

So-called brown dwarfs with masses of 2-8% the mass of the Sun most likely form like stars (and should be considered miniature Suns). At even lower masses we likely have a mix of objects formed like stars, and those formed like planets. In this proposal we want to investigate 'free-floating planetary-mass objects' (FFPMOs) which constitute hybrids between stars and planets with masses between 0.1 and 1% the mass of the Sun, or 1-10 times the mass of Jupiter. They include the lowest mass objects formed like stars, as well as ejected giant planets.

For this research we will use the outstanding capabilities of the James Webb Space Telescope (JWST). We will search for young FFPMOs, find out how many of them are formed in young clusters, and investigate possible signatures of their formation, such as motion, binarity and disks. Taken together, this will help us understand how the formation process changes with mass, and where the transition from star to planet formation happens.

It will also inform our knowledge of the early evolution of planetary systems, where ejected planets have formed before they got kicked out. These rogue planets are perhaps the most important population of exoplanets that we have not found thus far. This project will give us first important insights into their frequency and their formation.

A final intriguing question regarding FFPMOs is whether or not these objects, with masses comparable to those of giant planets, can themselves form their own miniature planetary systems, which could also be referred to as exomoons. With this proposal, we will investigate dusty disks around FFPMOs and probe for signs of ongoing planet formation, which will tackle this question as well.