Interstellar objects (ISOs) have intrigued scientists since the arrival of 'Oumuamua' in 2017, marking the first confirmed ISO to traverse the Solar System. In 2019, 'Comet 2i/Borisov' followed, representing the only two known ISOs that have visited our cosmic neighborhood.
However, countless ISOs likely passed through the Solar System throughout history, with future visits anticipated due to advancements in observational capabilities, such as the Vera Rubin Observatory.
The possibility of an ISO or solitary planet becoming a permanent member of the Solar System hinges on phase space, a mathematical framework describing dynamic systems like planetary orbits. The trajectories and interactions of ISOs within this space can lead to temporary or permanent capture.
Phase space encompasses all possible orbital configurations around the Sun, using position and momentum as coordinates. Within this complex framework, two types of capture points exist.
The first are weak capture points, allowing objects to enter semi-stable orbits temporarily, often near the boundaries of gravitational fields.
The second are permanent capture points. Objects captured here remain gravitationally bound indefinitely in stable orbits.
Permanent capture occurs when an object's angular momentum and energy precisely match these regions. Subtle changes in phase space can shift objects between weak and permanent capture, with variables like orbital eccentricity and semi-major axes playing significant roles.
A study by Edward Belbrun from Yeshiva University and James Green from Space Science Endeavors investigates this dynamic. Their research, titled 'Permanent Capture in the Solar System,' delves into the theoretical mechanics of phase space and ISO capture.
The authors describe permanent capture as the continual binding of a small body from interstellar space to the Sun, occurring when the body cannot escape back into interstellar space and remains trapped within the Solar System indefinitely, moving through this space without colliding with the Sun.
Unlike previous studies that focused on Jupiter as a third body in the three-body problem, this research considers the tidal forces of the galaxy, offering new insights. These forces significantly influence the structure of phase space, enhancing the potential for ISO capture.
Solitary planets abound in cosmic space due to early planetary dispersal and gravitational interactions.
The final architecture of any Solar System will be shaped by the dispersal of planets and the flybys of star-forming systems, as such close encounters can eject planets and small bodies from systems, creating what are termed solitary planets. This suggests that solitary planets may outnumber stars, although the authors note that this claim is somewhat controversial.
Nearby stars frequently pass close to the Solar System, with six such close encounters predicted over the next 50,000 years. These encounters could remove objects from the Oort Cloud or facilitate the capture of ISOs through the Sun's Hill gravitational region, which extends 3.81 light-years toward or away from the galactic center.
New research also indicates that ISOs or solitary planets could be weakly captured in the Solar System, moving chaotically while avoiding collisions. Such intrusions could disturb planetary orbits, leaving visible traces.
The Vera Rubin Observatory may transform our understanding of ISOs, revealing their distribution and potential as long-term residents of the Solar System. With advanced research, the idea of a visiting interstellar object becoming a permanent neighbor is increasingly plausible.