Giant rogue planets could host scaled-down planetary systems

Giant rogue planets could host scaled-down planetary systems
by Sophie Jenkins
London, UK (SPX) Aug 06, 2025

New findings from the University of St Andrews suggest that giant free-floating planets, unbound to any star, could form their own miniature planetary systems.

Using data from the James Webb Space Telescope (JWST), researchers examined eight isolated planetary-mass objects between five and ten times the mass of Jupiter. Although similar in size to gas giants, these bodies drift alone in space rather than orbiting stars.

Free-floating planets are difficult to detect because they are extremely faint and emit mostly infrared radiation. Despite this, they hold vital clues to how the smallest astronomical bodies form. Scientists believe many arise from collapsing gas clouds, much like stars, though others may originate in orbit around stars and be ejected later.

A multinational team of researchers, led by the University's School of Physics and Astronomy, observed the eight young rogue planets using two highly sensitive infrared instruments aboard JWST. The data, collected between August and October 2024, provided unprecedented spectroscopic detail.

The analysis confirmed that all objects have Jupiter-like masses. Six displayed excess infrared emission, a signature of surrounding warm dust disks - the environments where planets typically begin to form. The spectroscopic data also revealed silicate grain emissions within these disks, indicating early dust growth and crystallization, essential stages in rocky planet development. While such features have previously been observed around stars and brown dwarfs, this is the first confirmed detection in planetary-mass objects.

These results build on earlier research from St Andrews showing that disks around free-floating planetary bodies can survive for millions of years - long enough to potentially form planets.

Dr Aleks Scholz, the project's principal investigator, stated: "Taken together, these studies show that objects with masses comparable to those of giant planets have the potential to form their own miniature planetary systems. Those systems could be like the solar system, just scaled down by a factor of 100 or more in mass and size. Whether or not such systems actually exist remains to be shown."

Lead author Dr Belinda Damian added: "These discoveries show that the building blocks for forming planets can be found even around objects that are barely larger than Jupiter and drifting alone in space. This means that the formation of planetary systems is not exclusive to stars but might also work around lonely starless worlds."

Research Report:Spectroscopy of Free-Floating Planetary-Mass Objects and their disks with JWST