Solution to a cosmic mystery: the eccentric orbits of trans-Neptunian objects

New evidence suggests that billions of years ago, a star passed very close to our solar system. As a result, thousands of small celestial bodies located outside the solar system, outside the orbit of Neptune, were deflected into highly inclined paths around the sun. It is possible that some of them were captured by the planets Jupiter and Saturn as moons.

These results come from a team of astrophysicists from Forschungszentrum Jülich and Leiden University in the Netherlands. They were published in two studies in the journals Astronomy of nature And Letters from the Astrophysical Journal.

When we think of our solar system, we usually think of it as ending at the most distant known planet, Neptune. “However, we know that several thousand celestial bodies move beyond Neptune’s orbit,” says Susanne Pfalzner, an astrophysicist at the Jülich Research Center.

It is even suspected that there are tens of thousands of objects with a diameter greater than 100 kilometers. “Surprisingly, many of these so-called trans-Neptunian objects move in eccentric orbits, inclined relative to the common orbital plane of the planets of the solar system.”

Together with her Juliers colleague Amith Govind and Simon Portegies Zwart from Leiden University, Susanne Pfalzner used more than 3,000 computer simulations to investigate a possible cause of the unusual orbits: Could another star have caused the strange orbits of the trans-Neptunian objects?

The three astrophysicists discovered that a particular close flyby of another star can explain the inclined and eccentric orbits of known trans-Neptunian celestial bodies. “We can even deduce the orbits of very distant objects, such as that of the dwarf planet Sedna, discovered in 2003 at the edge of the solar system.”

“And also objects that move in orbits almost perpendicular to those of the planets,” explains Susanne Pfalzner. Such a flyby could even explain the orbits of 2008 KV42 and 2011 KT19, the two celestial bodies that move in the opposite direction to that of the planets.

“The best match to the current outer solar system that we found through our simulations is a star that is slightly lighter than our Sun, about 0.8 solar masses,” says Pfalzner’s colleague Amith Govind. “This star passed our Sun at a distance of about 16.5 billion kilometers. That’s about 110 times the distance between Earth and the Sun, or just under four times the distance to the outermost planet, Neptune.”

But what surprised scientists most was that the flyby of an alien star billions of years ago could also provide a natural explanation for phenomena closer to home. Susanne Pfalzner and her colleagues discovered that in their simulations, some trans-Neptunian objects were thrown into our solar system, in the region of the outer giant planets Jupiter, Saturn, Uranus and Neptune.

“Some of these objects could have been captured by the giant planets as moons,” says Simon Portegies Zwart of Leiden University. “This would explain why the outer planets of our solar system have two different types of moons.”

Unlike regular moons, which orbit the planet in circular orbits, irregular moons orbit the planet at a greater distance in inclined and elongated orbits. Until now, there was no explanation for this phenomenon.

“The beauty of this model is its simplicity,” Pfalzner says. “It answers several open questions about our solar system with a single cause.”