A star that passed close to our solar system several billion years ago may have perturbed outer solar system objects, according to a new study based on computer simulations led by Susanne Pfalzner of the Max Planck Institute for Radio Astronomy in Bonn, Germany.
Many dwarf planets and smaller Trans-Neptunian Objects (TNOs) beyond the orbit of Pluto have extremely inclined, eccentric orbits, which scientists are hard pressed to explain. For example, dwarf planet Sedna takes 11,400 years to complete a single orbit around the Sun.
Additionally, the outer solar system is emptier than researchers think it should be.
Although Neptune orbits further from the Sun than Uranus, it is more massive, posing yet another puzzle.
These anomalies led researchers to propose a rogue star passed close to the solar system in its early days, in the process scattering thousands of distant, icy worlds into unusual positions and orbits.
“You could well have a hybrid scenario, where the movement of the planets is responsible for the things we find in the inner solar system, like the low mass of Mars, and a flyby [is responsible] for the properties of the outer solar system,” Pfalzner said.
Using data on the behavior of young stars, the researchers conducted a computer simulation of a stellar flyby to determine whether the passage of a rogue star could have caused the current arrangement of the outer solar system.
According to the simulation, the chances of a star having done this over a period of one billion years are approximately one in four, meaning this likely occurred at some point in the solar system’s early years.
Specifically, the simulation determined that a star with a mass similar to that of our Sun could have created the dynamics seen in the outer solar system if it passed within 80 to 100 astronomical units (AU, with one AU equal to the average Earth-Sun distance or 93 million miles) while the system was still forming.
During its passage, the star could have flung thousands of tiny, icy worlds beyond Pluto into interstellar space, leaving the outer solar system with the empty regions it has today.
The researchers plan to further test their theory by adding more detail to their computer simulations.