An unidentified interstellar object may have altered the orbits of planets in our Solar System.

The orbits of the planets in the Solar System do not lie flat in the same plane. As a reference point, astronomers use the plane of Earth's orbit, known as the ecliptic plane. No other planet's orbital plane coincides with it; all are slightly tilted at different angles: for instance, Mercury's tilt is seven degrees, Mars's is less than two, Jupiter's is just over one, and Saturn's is two and a half. Additionally, the orbits are somewhat elongated.

These are clear signs of gravitational disturbances experienced by the system, as emphasized by astrophysicists from the University of Toronto (Canada) and the University of Arizona (USA) in their recent paper (available on the Cornell University preprint server). They explained that during the initial formation of worlds in the protoplanetary disk, they originate on perfectly circular orbits, rotating precisely in the plane of the solar equator. In our system, this would have remained the case to this day if nothing had interfered.

Generally, the dynamics of the planets are explained by internal processes, meaning the interactions of celestial bodies within the system. The most widely accepted model currently is the so-called Nice model (developed at the observatory located there). It posits that initially, a dense and fairly massive belt of small celestial bodies was located at the outskirts of the Solar System, which gradually shifted and displaced the gas giants.

Nevertheless, the authors of the new study stated that no theory proposed so far fully explains the current state of the Solar System. The scientists attempted to find a new answer to this question: they suggested that the planets arrived at their present situation under external influence.

Previously, there were suspicions that another star might have passed close to us and disturbed the system with its gravity. Now, researchers decided to explore another possibility: the influence of a planet or a brown dwarf instead of a star. It should be noted that brown dwarfs are considered to be bodies with a mass of at least 13 times that of Jupiter. These are so-called substellar objects where weak thermonuclear reactions can occur.

Astronomers modeled numerous scenarios for the appearance of such an object from interstellar space and concluded that it is quite possible for a body with a mass ranging from two to 50 Jupiters to have passed on a hyperbolic trajectory, at a distance of about 20 astronomical units from the Sun, which is a maximum of 20 times farther from our star than Earth. Currently, Uranus is located 19 astronomical units from the Sun.

The most likely scenario among all considered is the visitation of the Solar System by a planet with a mass of eight Jupiters, which ended up at 1.69 astronomical units from the Sun — slightly farther than Mars's current position.

This scenario appears increasingly realistic thanks to new discoveries in recent years. Firstly, there is the asteroid 'Oumuamua and the comet Borisov — the first known celestial bodies from interstellar space; and secondly, the so-called free-floating planets — worlds not belonging to any stars.