When interstellar visitors like Oumuamua (2017) and Comet 2I/Borisov (2019) passed through our Solar System, they sparked curiosity about the possibility of such objects being captured permanently. New research reveals that under the right conditions, our Sun could gravitationally adopt an interstellar object (ISO) or even a rogue planet, potentially adding a new member to the Solar System.

The Role of Phase Space in Capturing Celestial Wanderers

At the core of this scenario lies phase space, a mathematical framework used to describe the dynamics of systems like our Solar System. Phase space incorporates both position and momentum to map all potential orbital configurations. Within this multidimensional landscape, there are regions—capture points—where objects can be temporarily or permanently bound by the Sun’s gravity.

The research, published in Celestial Mechanics and Dynamical Astronomy by Edward Belbruno and James Green, identifies two types of capture points:

  • Weak Capture Points: Areas where an object can enter a semi-stable orbit temporarily, often influenced by gravitational nudges.
  • Permanent Capture Points: Regions where an object’s energy and momentum allow it to remain indefinitely in a stable orbit.

Subtle changes in an object's trajectory or the gravitational dynamics of the Solar System can determine whether an ISO becomes permanently bound or merely visits briefly before escaping.

Theoretical Insights Into Permanent Capture

The study introduces the concept of permanent weak capture, where an object is gravitationally bound to the Sun but never achieves a fully stable orbit. Instead, it asymptotically approaches a capture state, avoiding collisions with the Sun.

Unlike earlier studies focusing on Jupiter’s role in capturing objects, this research incorporates the galaxy’s tidal forces alongside the Sun and the ISO, offering a more comprehensive perspective. The findings suggest that openings in the Sun’s Hill sphere—a region where the Sun's gravity dominates over external forces—could enable permanent weak capture of ISOs or rogue planets.

Could a Rogue Planet Join Our Solar System?

Rogue planets, which wander freely through interstellar space after being ejected from their home systems, are believed to vastly outnumber stars. The researchers calculate that within six parsecs (about 20 light years) of the Sun, there are 131 stars and brown dwarfs, many of which may host undiscovered planets.

Stellar encounters occur frequently on cosmic timescales. Every million years, approximately two stars pass within a few light years of the Sun. Some of these interactions could dislodge objects from the Oort Cloud, sending them toward the inner Solar System. Such disturbances may create opportunities for objects to find their way to the capture points identified in the study.

What Would Happen if a Rogue Planet Stayed?

A rogue planet captured by the Sun could cause significant changes, depending on its mass and orbit. It might disrupt existing planetary orbits, potentially affecting Earth’s climate or even life itself. However, such scenarios are highly improbable and depend on many variables.

Even without dramatic disruptions, a new planetary member would be a scientific treasure trove, offering insights into interstellar dynamics and planetary formation.

Looking Ahead

The Vera Rubin Observatory, set to begin operations soon, is expected to revolutionize our understanding of ISOs and rogue planets by identifying more of these objects and tracking their movements. This may help scientists pinpoint regions where ISOs cluster or avoid, as well as uncover potential candidates for capture.

As the researchers conclude, the possibility of permanent weak capture opens the door to fascinating new chapters in Solar System dynamics. A rogue planet could one day find itself permanently adopted by the Sun, offering scientists a unique opportunity to study a celestial traveler that decided to stay.