A new study may finally explain how planets can end up orbiting their stars at extremely large distances—sometimes hundreds or even thousands of times farther than Earth is from the Sun.
These distant worlds, known as “wide-orbit” planets, have long puzzled astronomers.
But now, scientists from Rice University and the Planetary Science Institute think they’ve found a natural explanation—and it might even support the idea that a mysterious Planet Nine could be hiding in our solar system.
Published in Nature Astronomy, the study used thousands of computer simulations to recreate the early days of planetary systems.
According to the researchers, when stars are newly formed, they often sit in crowded clusters surrounded by other young stars.
At the same time, planets are still forming and moving around in chaotic ways. Giant planets often push each other around through strong gravitational interactions—some even get flung far away from their stars.
But if the timing is right and nearby stars are in just the right positions, these scattered planets don’t get thrown into space. Instead, they settle into very wide orbits.
Lead author André Izidoro explained it like watching a game of cosmic pinball. Planets bounce around in the early solar system, and sometimes, one gets knocked out to the edge—but doesn’t go flying away entirely. These wide-orbit planets then stay quietly circling their star at a great distance.
The team found that wide-orbit planets, defined as orbiting between 100 and 10,000 times farther than Earth from the Sun, are more common than we might think.
Their simulations showed that in solar systems similar to ours, about 5–10% of scattered planets can end up in these wide orbits. That’s enough to expect one such planet for every thousand stars.
This idea could also explain the long-debated Planet Nine—a theoretical planet believed to exist far beyond Neptune.
While no one has seen it directly, the strange orbits of some icy objects in the outer solar system suggest something large is tugging on them.
According to the study, if the early solar system experienced two periods of instability—when Uranus and Neptune were forming and later when the giant planets scattered—there could be up to a 40% chance that a Planet Nine-like object was trapped far out.
The study also helps explain why some planets get completely ejected and end up floating through space alone. These “rogue planets” are likely the unlucky ones that didn’t get caught in orbit.
Looking ahead, astronomers are excited about the upcoming Vera C. Rubin Observatory, which will scan the sky in greater detail than ever. It could be the key to finally spotting Planet Nine—or confirming that it doesn’t exist at all.
