Imagine a giant planet drifting far beyond the known edges of a solar system, hundreds of times farther from its star than Earth is from the Sun.
Astronomers have spotted such distant giants around other stars, and some believe our own Sun might be hiding one too. The elusive Planet Nine, a mysterious world that could be tugging on the orbits of icy objects way out past Neptune.
But how do these far-flung giants end up in such lonely orbits?
Scientists at Rice University and the Planetary Science Institute ran thousands of simulations and discovered something wild. These wide-orbit planets might be cosmic leftovers from the chaotic early days of star systems.
Back then, stars were born in crowded clusters, and planets were like pinballs are bumping, bouncing, and sometimes getting flung to the outer edges. If the timing was just right, some of these planets didn’t escape entirely; instead, they got trapped in distant orbits.
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Even cooler? Systems like ours are especially good at catching these planetary wanderers. So the idea of a hidden ninth planet in our backyard isn’t just sci-fi, it’s becoming more scientifically plausible.
To understand how giant planets end up on super-distant orbits, scientists ran thousands of simulations of different planetary systems: some like ours, others with wild setups like twin suns. They placed these systems inside realistic star clusters, where stars are born close together.
They found that in the early chaos of a young system, planets often get shoved outward by gravitational tugs from their neighbors. If a nearby star gives the planet a gentle nudge at just the right time, it can lock the planet into a distant orbit, far from the inner planets.
These planets end up “frozen” in place once the star cluster breaks apart. These wide-orbit planets sit between 100 and 10,000 AU from their star, way beyond where most planets form.
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Scientists may be closer to solving the mystery of Planet Nine, a hidden world thought to orbit far beyond Neptune, between 250 and 1,000 times farther from the Sun than Earth. Though we haven’t seen it directly, the strange paths of distant icy objects suggest something massive is tugging on them.
New simulations show there’s up to a 40% chance that a Planet Nine-like object could have been captured during the early chaos of our solar system’s formation.
The study also connects these distant giants to rogue planets, lonely worlds that got kicked out of their home systems and now drift through space.
As researcher Nathan Kaib put it, “Not every scattered planet is lucky enough to get trapped. Most are flung into the galaxy, but some stick around in wide, frozen orbits, giving us a link between the planets we see on the edge and the ones we find wandering in the dark.”
Scientists are exploring how some planets get flung far from their stars, but don’t escape entirely. This idea, called “trapping efficiency,” measures how likely a scattered planet is to stay in a wide orbit instead of drifting off into space.
They found that solar systems like ours are pretty good at trapping these distant planets, with a 5–10% success rate. Other systems, like those with only ice giants or two suns, aren’t as efficient.
On average, there may be one wide-orbit planet for every thousand stars. That might sound rare, but across billions of stars, it adds up fast.
The study also gives exoplanet hunters a new roadmap: Wide-orbit planets are most likely to be found around metal-rich stars that already have gas giants. These systems are perfect targets for future deep-space imaging. And there’s more if Planet Nine exists, the upcoming Vera C. Rubin Observatory might be the one to spot it.
Journal Reference
- Izidoro, A., Raymond, S.N., Kaib, N.A., et al. Very-wide-orbit planets from dynamical instabilities during the stellar birth cluster phase. Nat Astron (2025). DOI: 10.1038/s41550-025-02556-0
