In the past decade, astronomers have observed three interstellar objects (ISOs) passing through the solar system. These include the enigmatic ‘Oumuamua in 2017, the interstellar comet 2I/Borisov in 2019, and 3I/ATLAS in July 2025. This latest object also appears to be a comet, based on recent observations that showed it was actively releasing water vapor as it neared the Sun.
The detection of these objects, which were previously theorized but never observed, has sparked interest in the origins of ISOs, their dynamics, and where they may be headed once they leave the solar system.
Studying interstellar objects
Since asteroids and comets are essentially material left over from the formation of planets, studying ISOs could reveal what conditions are like in other star systems without having to send interstellar missions there.
In a recent paper being reviewed for publication in Astronomy & Astrophysics, Shokhruz Kakharov and Prof. Abraham Loeb calculated the trajectories of all three interstellar visitors to determine from where they came and to apply age constraints. Their results indicate these ISOs originated from different regions in the Milky Way’s disk, and range in age from one to several billion years.
Origins and trajectories
Kakharov is a graduate student at Harvard University’s Astronomy Department whose work includes studies on interstellar objects, the trajectories of spacecraft like Voyager, direct imaging, and the flux of extragalactic dark matter. Prof. Loeb is the Frank B. Baird Jr. Professor of Science at Harvard University and the Director of the Institute for Theory and Computation (ITC) at the Harvard & Smithsonian Center for Astrophysics (CfA).
The discovery of ‘Oumuamua kicked off a revolution in astronomy, confirming the existence of ISOs and inspiring efforts to study them closer. As Kakharov told Universe Today via email, they’ve also transformed our understanding of galactic dynamics and the formation of planetary systems.
Before 1I/’Oumuamua’s discovery in 2017, we had no direct evidence that objects from other star systems could reach our solar system. These visitors provide unique samples of material from distant planetary systems, offering insights into the chemical composition and physical properties of exoplanetary material that we cannot obtain through remote observations alone, Kakharov explained.
They also serve as natural probes of the interstellar medium and galactic dynamics, revealing the gravitational interactions that shape stellar populations over billions of years.
Understanding ISO origins
Understanding ISO origins provides a deeper context for interpreting their physical and chemical properties. For example, knowing that 3I/ATLAS likely originated from an old stellar population suggests it may have experienced different evolutionary processes than younger objects.
This information helps us understand the diversity of planetary system architectures and the conditions under which objects are ejected into interstellar space. Also, tracing their origins helps identify potential source regions and ejection mechanisms, whether through gravitational scattering, stellar evolution, or other dynamical processes.
For their purposes, Kakharov and Loeb ran a series of Monte Carlo numerical simulations using the GalPot galactic potential model, a software package designed to calculate the gravitational potential of a galaxy.