The James Webb Space Telescope has detected six possible rogue planets—objects that resemble planets in size but are not gravitationally bound to any stars. Among them is the lightest one ever observed, which is accompanied by a dusty disk. This intriguing discovery suggests that the cosmic processes responsible for star formation may also contribute to the creation of objects that are only slightly larger than Jupiter.
The James Webb Space Telescope has detected six possible rogue planets—objects that resemble planets in size but are not gravitationally attached to any stars—one of which is the lightest identified to date and comes with a dusty disk surrounding it.
These rare objects provide new insights indicating that the same cosmic processes that form stars could also be involved in creating bodies that are just a bit larger than Jupiter.
“We are exploring the very boundaries of the star formation process,” explained lead author Adam Langeveld, an astrophysicist at Johns Hopkins University. “If we encounter an object that resembles a young Jupiter, might it have transformed into a star under the right conditions? This is crucial for understanding the formation of both stars and planets.”
The results stem from Webb’s most in-depth survey of the young nebula NGC1333, a star-forming cluster located about a thousand light-years away in the Perseus constellation. Today, the European Space Agency released a new image showcasing NGC1333, filled with stunning displays of interstellar dust and clouds. A paper detailing these findings is set to be published in The Astronomical Journal.
Data obtained from Webb indicates that the worlds discovered are gas giants, with masses ranging from five to ten times that of Jupiter. This suggests they are some of the lightest objects known to have emerged from processes typically creating stars and brown dwarfs—objects that lie between being a star and a planet but never ignite hydrogen fusion and eventually diminish.
“We leveraged Webb’s unprecedented sensitivity in infrared wavelengths to search for the faintest constituents of a young star cluster, aiming to answer a core question in astronomy: What is the lightest object that can form like a star?” said Ray Jayawardhana, Johns Hopkins Provost, and co-author of the study. “It appears that the smallest independent objects forming like stars are similar in mass to giant exoplanets orbiting nearby stars.”
No objects lighter than five Jupiter masses were observed, even though the telescope had the capability to detect them. This strongly suggests that any stellar objects lighter than this marker are likely to form in a manner similar to planets, according to the authors’ conclusions.
“Our observations validate that nature produces planetary-mass objects through at least two distinct processes—via the contraction of gas and dust clouds, akin to star formation, and within gas and dust disks surrounding young stars, similar to how Jupiter formed within our solar system,” Jayawardhana illuminated.
The most fascinating of these starless objects is also the lightest, estimated to possess a mass equivalent to five Jupiters (around 1,600 Earths). The existence of a dusty disk surrounding it indicates that this object most likely formed like a star, as cosmic dust typically spins around a core in the early stages of star formation, according to Langeveld, a postdoctoral researcher in Jayawardhana’s group.
These disks are essential for planet formation, hinting that the findings may have significant implications for understanding “mini” planets.
“These small objects, with masses comparable to giant planets, could potentially form their own planets,” noted co-author Aleks Scholz, an astrophysicist from the University of St Andrews. “This might serve as a nursery for a miniature planetary system, distinct from our solar system’s scale.”
Utilizing the NIRISS instrument on Webb, the astronomers studied the infrared light profiles (or spectra) of every object in the surveyed region of the star cluster and reanalyzed 19 known brown dwarfs. They also discovered a new brown dwarf with a planetary-mass companion—an uncommon discovery that challenges existing theories on the formation of binary systems.
“It’s likely that such pairs formed similarly to binary star systems, arising from a fragment of a cloud as it collapsed,” Jayawardhana explained. “The incredible variety of systems nature has produced is noteworthy and compels us to refine our models of star and planet formation.”
Rogue worlds might originate from collapsing molecular clouds that do not possess adequate mass for the nuclear fusion necessary for star formation. They could also arise from the aggregation of gas and dust in disks around stars into planet-like spheres that are eventually expelled from their star systems, likely due to gravitational interactions with other celestial bodies.
These free-floating objects complicate our classification of celestial bodies since their masses overlap with those of gas giants and brown dwarfs. Although such objects are thought to be rare in the Milky Way galaxy, data from Webb indicates that they represent approximately 10% of the celestial bodies in the studied star cluster.
In the next few months, the research team will analyze the atmospheres of more faint objects and compare them to heavier brown dwarfs and gas giant planets. They have also secured time on the Webb telescope to investigate similar objects possessing dusty disks to examine the likelihood of forming mini planetary systems akin to the various moons of Jupiter and Saturn.
Additional contributors to the research include Koraljka Muži? and Daniel Capela from Universidade de Lisboa; Loïc Albert, René Doyon, and David Lafrèniere from Université de Montréal; Laura Flagg from Johns Hopkins; Matthew de Furio from the University of Texas at Austin; Doug Johnstone from the Herzberg Astronomy and Astrophysics Research Centre; and Michael Meyer from the University of Michigan, Ann Arbor.
The Deep Spectroscopic Survey for Young Brown Dwarfs and Free-Floating Planets employed the Near Infrared Imager and Slitless Spectrograph (NIRISS) on the James Webb Space Telescope, a collaborative effort involving NASA, the European Space Agency, and the Canadian Space Agency.
The authors express gratitude for the support from the UKRI Science and Technology Facilities Council, the Fundação para a Ciência e a Tecnologia (FCT), the U.S. National Science Foundation, and the National Research Council of Canada.
