The James Webb Space Telescope (JWST) has made a significant discovery within the depths of the Perseus Molecular Cloud. Half a dozen free-floating planets, ranging in size from five to 10 times the mass of Jupiter, have been identified by the powerful observatory. What sets these planets apart is the fact that they do not orbit a star but are thought to have formed like stars themselves, directly condensing from interstellar gas.

In an intriguing revelation, one of the rogue planets has been found to be surrounded by a disk of gas and dust, indicating the potential formation of moons or other celestial bodies. This is not the first time that the JWST has come across such free-floating planets, as approximately 40 binary pairs of gas giant planets were discovered in the Orion Nebula back in 2023. However, the six newly discovered objects in NGC 1333, a combination of a reflection nebula and open star cluster located 960 light-years away, offer valuable insights into the process of their formation.

Although the JWST has the capability to detect rogue planets smaller than five times the mass of Jupiter, none were found within NGC 1333. This observation sheds light on the formation of these free-floating planets. While the planets in our own solar system were born through a bottom-up process, growing larger by accreting raw materials from a protoplanetary disk, the top-down formation process occurs when planets collapse directly from a cloud of gas and dust, much like how stars are formed. The absence of free-floating planets in the range of one to five times the mass of Jupiter strongly suggests that five Jupiter masses is the lower limit for the top-down formation process.

Astrophysicist Ray Jayawardhana of Johns Hopkins University, a participant in the new discoveries, states, "Our observations confirm that nature produces planetary mass objects in at least two different ways - from the contraction of a cloud of gas and dust, similar to how stars form, and in disks of gas and dust around young stars, just as Jupiter did in our own solar system." This finding is significant as it highlights the overlap in size and mass between the smallest objects formed like stars and some of the largest worlds formed bottom-up that orbit stars.

These discoveries further blur the boundaries between what can be classified as a planet and what cannot. To be considered a star, an object must undergo nuclear fusion reactions that convert hydrogen into helium to generate energy. The minimum mass required for this process is approximately 9% the mass of our sun, equivalent to about 93 times the mass of Jupiter. Objects smaller than this are categorized as brown dwarfs, gaseous entities that are not quite stars but too massive to be considered planets. Some brown dwarfs can produce energy from the fusion of deuterium. With masses down to about 13 times that of Jupiter, anything smaller was previously assumed to be a planet orbiting a star.

The intriguing discovery made by the JWST not only adds to our understanding of how planets form but also challenges our existing definitions of planetary objects. These orphaned planets drifting through the Perseus Molecular Cloud continue to fascinate astronomers as they unravel the mysteries of the universe and explore the diverse ways celestial bodies come into existence.