As 3I/ATLAS is presently fascinating space enthusiasts, researchers say that such interstellar objects may act as planetary seeds, becoming trapped in planet-forming disks around young stars and eventually growing into giant planets.
The new research finally overcomes obstacles for such an event to occur that earlier work was unable to explain. The “3I” in 3I/ATLAS denotes it is the third such interstellar object detected since 2017, following on from 1I/‘Oumuamua and 2I/Borisov.
The Impact of Interstellar Objects
The new findings were presented at the EPSC-DPS2025 Joint Meeting in Helsinki by Professor Susanne Pfalzner of Forschungszentrum Jülich in Germany. While what the objects may be has generated speculation that includes some rather unusual ideas, astronomers generally agree that they are most likely natural objects.
However, Professor Pfalzner says that they may have a more significant impact on the world around them than it first appears. Pfalzner worked with a team of researchers to demonstrate that these cosmic travelers may eventually set down roots.
“Interstellar objects may be able to jump start planet formation, in particular around higher-mass stars,” said Pfalzner.
Planet Formation
The most commonly accepted theory of planet formation centers on dusty disks surrounding young stars. Tiny particles within these disks begin to lump together as larger formations called “planetesimals,” which eventually snowball until a full-size planet is born through the process called accretion.
While the theory is widely held, it has remained imperfect, as models struggled to produce anything larger than a meter in size through this process. Most models depicting such collisions show these boulder-sized objects not sticking together, but bouncing off one another or shattering into even smaller pieces instead.
Pfalzner discovered that one solution to this unsticky boulder problem may involve interstellar objects. Pfalzner employed new models that demonstrated interstellar objects that were close to the size of ’Oumuamua, the first interstellar object observed by astronomers. At a length of roughly 100 meters, these objects could become stuck in planet-forming disks, held by the gravitational pull of the young star at the center.
“Interstellar space would deliver ready-made seeds for the formation of the next generation of planets,” Pfalzner said.
Time Vs Gas Giants
Interstellar objects may hold the key to another puzzle, which involves the formation of gas giants. As would be expected from their name, the processes that give rise to giant planets are time-consuming processes, and ones that researchers do not think can be easily rushed. The main problem is that the types of stars that typically host gas giants are Sun-like stars, whose planet-forming disks have short lifespans. Smaller, cooler stars called “M dwarfs,” with typically longer-lasting planet-forming disks, rarely host gas giants.
Interstellar objects may be able to greatly speed up gas giant formation processes, allowing them to fit within available windows because the accretion process will not have to begin at zero. Larger pieces, and more of them, will become stuck on these interstellar “cosmic seeds,” allowing for a much faster development into a full-size gas giant.
“Higher-mass stars are more efficient in capturing interstellar objects in their discs,” said Pfalzner. “Therefore, interstellar object-seeded planet formation should be more efficient around these stars, providing a fast way to form giant planets. And, their fast formation is exactly what we have observed.”
Pfalzner has already outlined plans to continue this line of research, with the next step being to model how many interstellar objects that become trapped in these planet-forming disks actually evolve into planets. Another element Pfalzner plans to investigate in future models is whether the objects are captured in an even distribution across the disk, or whether certain factors can create hot spots most likely to trap an interstellar object.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.