The findings of 1I/Oumuamua, 2I/Borisov, and 3I/ATLAS have revealed a substantial number of interstellar objects in the cosmos. Their widespread presence suggests that such objects are also found in protoplanetary disks, essential sites for planet formation. In these disks, interstellar objects could potentially bypass the 1-meter (3.3-foot) barrier in the traditional model of planet formation, initiating the creation of giant exoplanets.
This colorized image was taken by the CaSSIS instrument aboard ESA’s Trace Gas Orbiter on October 3, 2025, and displays the interstellar comet 3I/ATLAS. Image credit: ESA/TGO/CaSSIS.
Interstellar objects, including asteroids and comets, are those that have been expelled from their original star systems and are now traversing interstellar space, occasionally intersecting with other star systems.
Since 2017, astronomers have identified three interstellar objects passing through our solar system: 1I/’Oumuamua, 2I/Borisov, and the latest, 3I/ATLAS.
“Nevertheless, interstellar objects may exert a more significant influence than it appears at first glance,” states Professor Susanne Falzner, an astronomer at Jülich National Park.
“Interstellar objects could potentially incite planet formation, particularly around high-mass stars.”
Planets are formed from dusty disks that surround young stars through a process known as accretion. This theory posits that smaller particles gradually coalesce into larger objects, culminating in the formation of planet-sized bodies.
However, researchers have faced challenges in explaining how accretion can create objects larger than a meter amidst the chaotic collisions of planet-forming disks surrounding young stars. In simulations, the rocks tend to either bounce off each other or break apart upon collision, rather than adhering together.
Interstellar objects might help circumvent this issue. The researchers’ model illustrates how the dust-laden disks surrounding young stars can gravitationally capture millions of interstellar objects akin to 1I/’Oumuamua, which is estimated to be around 100 meters (328 feet) long.
“Interstellar space will supply ready-made seeds for the next phase of planet formation,” said Professor Falzner.
If interstellar objects could act as seeds for planets, it would also resolve another enigma.
Gas giant planets like Jupiter are scarce around smaller and colder stars, referred to as M dwarfs, but are more frequently found around larger stars similar to the Sun.
However, the lifespan of a planet-forming disk around a Sun-like star lasts only about 2 million years before dissipating, complicating the formation of gas giant planets in such a brief time frame.
That said, if captured interstellar objects serve as seeds for accretion, the planet-forming process could hasten, allowing giant planets to form within the lifetime of the disk.
“The more massive a star is, the more effectively it can capture interstellar objects in its disk,” Professor Falzner explained.
“As a result, planet formation seeded with interstellar objects should proceed more efficiently around these stars, offering a rapid pathway to forming giant planets.”
“And their swift formation is precisely what we’ve observed.”
Professor Falzner presented her findings in September 2025 during the EPSC-DPS2025 joint meeting in Helsinki, Finland.
_____
S. Falzner. 2025. Interstellar objects primarily function as seeds for planet formation surrounding high-mass stars. EPSC abstract 18: EPSC-DPS2025-1927; doi: 10.5194/epsc-dps2025-1927
Source: www.sci.news
