A new study suggests that a planet-sized object may have altered the orbits of the four outer planets in our solar system, potentially explaining the unusual paths they follow today.
These planets — Jupiter, Saturn, Uranus, and Neptune — do not have perfectly circular orbits, and their paths do not lie precisely on the same plane, which has puzzled scientists for decades.
Planetary Scientist Offers New Explanation for the Odd Orbits of Outer Planets
Astronomers have long been trying to figure out how the planets in our solar system came to have these peculiar orbits. While most theories agree on the general pattern of how planets should orbit — nearly circular and in the same plane — no planet fits this exact model.
The orbits of the outer planets, in particular, show slight deviations, which have been difficult to explain. The discrepancy in these orbits has raised questions about how they were shaped over time.
A team of researchers, led by planetary scientist Renu Malhotra at the University of Arizona, proposed a new theory that could explain these oddities.
Instead of focusing on interactions between the planets themselves, they suggested that a star-sized object, which passed through the solar system around 4 billion years ago, may have been the cause. This mysterious "visitor" could have nudged the giant planets into their current orbits.
The team used computer simulations to test this theory. They ran 50,000 simulations over 20 million years, altering variables such as the size, speed, and proximity of the visiting object.
They expanded their search to include not only objects the size of stars but also smaller objects, as small as Jupiter itself.
The team also focused on situations where the object passed very close to the sun, within 20 astronomical units (AU), a distance roughly equal to 20 times the distance from Earth to the sun, Independent reported.
The simulations showed that in about 1% of cases, the interstellar object's passage caused the orbits of the outer planets to shift into the patterns we see today. In the closest matches, the object, which could have been as much as 50 times the mass of Jupiter, passed very close to the outer planets, even grazing the orbit of Mercury.
Massive Brown Dwarf May Have Altered Outer Planet Orbits
According to LiveScience, one of the simulations that closely matched the current solar system featured an object about eight times the mass of Jupiter, which came as close as 1.69 AU to the sun, just slightly farther than Mars' orbit.
The object's close pass was enough to alter the orbits of the outer planets, shifting them into their current positions.
The research suggests that such encounters may not be as rare as once thought. Because objects like brown dwarfs, which are too small to be stars but too massive to be planets, are relatively common in the universe, close encounters with these objects could be a regular occurrence.
While the study is still under review, it provides a compelling explanation for the unusual orbits of the outer planets and opens up new possibilities for understanding the formation and evolution of our solar system.
The researchers are now calling for further exploration of how such flybys could have affected not only the gas giants but also the rocky planets like Earth and Mars.
