Then in 2019, Comet 2l/Borisov did the same. These are the only two confirmed ISOs that have visited our solar system.
In the long history of our solar system, many more ISOs must have visited it, and many more will in the future. Clearly, there are more such objects, and the upcoming Vera Rubin Observatory is expected to discover many more.
It is possible that the Sun may capture an ISO or errant planet in the same way that some of the planets have captured moons.
It all comes down to phase space.
What would happen to our mature, peaceful solar system if it suddenly got another member? That would depend on the mass of the object and the eventual orbit it would end up in.
It's an interesting thought experiment; while Borisov and Oumuamua are smaller objects, a more massive rogue planet joining our solar system could cause orbital chaos. This could potentially alter the course of life on Earth, though this is highly unlikely.
How likely is this scenario? A new science note in Celestial Mechanics and Dynamical Astronomy outlines how our solar system could capture the ISO. It's titled "Permanent Capture in the Solar System," and the authors are Edward Belbruno of the Department of Mathematical Sciences at Yeshiva University and James Green, a former NASA employee.
Phase space is a mathematical representation that describes the state of a dynamical system such as our solar system. Phase space uses coordinates to represent both position and momentum.
It is like a multidimensional space that contains all possible configurations of orbits around the Sun. Phase space captures the state of a dynamical system by tracking both position and momentum characteristics. The phase space of our solar system has capture points at which the ISO may be gravitationally bound to the Sun.
The phase space is complex and is based on Hamiltonian mechanics. It involves things like orbital eccentricity, semimajor axis, and orbital inclination. Phase space is best understood as a multidimensional landscape.
The phase space of our solar system includes two types of pinch points: weak and permanent.
Weak intercept points are regions in space where an object may be temporarily attracted into a semi-stable orbit. These points are often located where the outer edges of the objects gravitational boundaries meet. They resemble gravitational nudging rather than orbit acceptance.
Permanent capture points are regions in space where an object can be permanently captured into a stable orbit. The angular momentum and energy of an object are the precise configuration that allows it to maintain an orbit. In planetary systems, these points of permanent capture are stable orbital configurations that persist for extremely long periods of time.
The phase space of our solar system is extremely complex and includes many moving bodies and their changing coordinates. Subtle changes in phase space coordinates can allow objects to transition between steady capture and weak capture states. By the same token, subtle differences in ISO or interstellar planets can lead them to these points.
In their research notes, the authors describe permanent ISO capture this way, "Permanent capture of a small body, P, around the Sun, S, from interstellar space occurs when P can never escape back into interstellar space and remains captured within the solar system for all future time, moving without collision with the Sun."
Purists will note that nothing can be the same for all future time, but the point remains.
Other researchers have looked at this scenario as well, but this work goes even further. "In addition to P being persistently captured, it is also weakly captured," they write.
It revolves around the notoriously difficult 3-body problem. Also unlike previous studies that used Jupiter as the third body, this work uses the tidal force of the galaxy as the third body, along with P and S.
"This tidal force has a significant effect on the structure of phase space for the range of velocities and distance from the Sun we consider," they explain in their paper.
The paper focuses on the theoretical nature of phase space and ISO capture. It explores "the dynamical and topological properties of a special type of persistent capture, called persistent weak capture, that occurs over infinitely long times."
An object in persistent weak capture will never escape, but will never reach a consistent, stable orbit. It asymptotically approaches the capture set without colliding with the star.
It is not disputed that interstellar planets probably exist in large numbers. Stars form in groups that eventually spread out over a larger area. Since stars host planets, some of these planets will be scattered by gravitational interactions before their companion stars acquire some distance from each other.
"The final architecture of any solar system will be shaped by the scattering of planets in addition to the stellar flybys of neighboring forming star systems, as close encounters can pull planets and small bodies out of the system, creating so-called interstellar planets," the authors explain.
"Taken together, the ejection of planets as a result of the early scattering of planets and stellar encounters, and in the subsequent evolution of a multi-planet solar system, should be a common occurrence and supports the evidence for a very large number of free-floating planets in interstellar space, perhaps exceeding the number of stars," the authors write, noting that this claim is controversial.
The researchers developed a cross-section to capture the solar system's phase space, then calculated how many interstellar planets are in the vicinity of our solar system.
There are 131 stars and brown dwarfs in the Solar System's neighbourhood, which extends to a radius of 6 parsecs around the Sun. Astronomers know that at least a few of them host planets, and it's very likely that all of them host planets we haven't yet discovered.
Every million years, about 2 of our stellar neighbors come within a few light-years of Earth. "However, six stars are expected to move closer together in the next 50,000 years," the authors write.
The outer boundary of the Oort Cloud is about 1.5 light-years away, so some of these stellar encounters could easily dislodge objects from the cloud and send them toward the inner solar system. This has happened many times before, as the cloud is likely the source of long-period comets.
The researchers identified openings in the solar system's phase space that could allow some of these objects, or ISOs, to reach a persistent faint capture.
These are apertures in the Sun's Hill-sphere, a region where the Sun's gravity is the dominant gravitational force for capturing satellites. These openings are located 3.81 light-years from the Sun in the direction of the galactic center or opposite to it.
"Persistent faint trapping of interstellar objects in the solar system is possible through these holes. They would move chaotically in the Hill sphere to permanent capture around the Sun, which takes an arbitrarily long time with infinitely many cycles," the authors state.
These objects would never collide with the Sun and could be captured permanently.
"An interstellar planet could disrupt the orbits of planets, which would be detectable," they conclude.
We're still at the beginning of understanding ISO. We know they are there, but we don't know how many there are or where they are. The Vera Rubin Observatory could open our eyes to this population of objects. It can even show how they cluster in some regions and avoid others.
If they happen to be near one of the openings of the Sun's hill-sphere, we may have a visitor who decides to stay. | BGNES
