The hunt for Planet Nine—a mysterious, unseen world lurking at the farthest reaches of our Solar System—has fascinated astronomers for years.
But while the discovery of such a planet would be groundbreaking, it might not be all good news.
In fact, new research suggests that in the distant future, Planet Nine could be responsible for catastrophic consequences, possibly ejecting one or more of our planetary neighbors from the Solar System entirely.
A Hidden Giant at the Edge of the Solar System
Earlier this year, astronomers detected evidence of a massive planetary body beyond Neptune, inferred from the erratic movements of Kuiper Belt Objects—icy bodies that orbit the Sun in the far reaches of the Solar System.
Their unusual motion strongly suggests the gravitational pull of an unseen giant planet, potentially ten times the mass of Earth and four times its size.
Though still hypothetical, the case for Planet Nine is growing stronger with every new piece of evidence.
In recent months, scientists have identified even more Kuiper Belt Objects with orbits that align with the presence of a distant, hidden planet.
If confirmed, it would reshape our understanding of the Solar System’s structure.
But not all scientists are celebrating.
Astrophysicist Dimitri Veras from the University of Warwick has looked beyond its discovery and into the long-term consequences of its existence.
His findings suggest that, billions of years from now, Planet Nine could spell disaster for the remaining planets of our system.
The Death of the Sun—and the Chaos That Follows
Fast forward about 7 billion years into the future. Our Sun, having exhausted its hydrogen fuel, will swell into a red giant, engulfing Mercury, Venus, and likely Earth.
After this dramatic expansion, it will then shed its outer layers and shrink into a small, dense white dwarf—a fate that awaits all sun-like stars.
As this transformation occurs, the gravitational forces holding the Solar System together will shift.
The outer planets—Jupiter, Saturn, Uranus, and Neptune—are expected to drift farther away from the Sun as its mass decreases.
However, Veras’ research suggests that Planet Nine, due to its vast distance and elongated orbit, may not move outward in the same way.
Instead, it could interact chaotically with the displaced planets, triggering gravitational disturbances that send one or more of them hurtling into deep space.
“The existence of a distant massive planet could fundamentally change the fate of the Solar System,” Veras explains.
“Uranus and Neptune, in particular, may no longer be safe from the death throes of the Sun.”
Is Planet Nine an Intruder?
This revelation turns a common assumption on its head: that the outer planets will simply drift into stable orbits as the Sun dies.
Instead, if Planet Nine exists, it could destabilize the entire post-Sun Solar System, sending some planets spiraling into interstellar space.
The irony? This scenario may have happened before—but in reverse. Some researchers believe Planet Nine itself might not have originated in our Solar System at all.
One prevailing theory suggests that it was an exoplanet that once orbited another star, only to be captured by our Sun’s gravity during a close encounter with another stellar system 4.5 billion years ago.
If true, this means Planet Nine was once an interstellar wanderer—potentially destined to send another planet into that same lonely fate.
The Fate of the Solar System—A Billion-Year Mystery
While this scenario remains theoretical, it adds a compelling twist to the ongoing search for Planet Nine.
If it exists, it could hold the key to understanding not just our Solar System’s present, but also its distant future.
The findings, which will be published in the Monthly Notices of the Royal Astronomical Society, suggest that the ultimate fate of our planetary system could depend on the properties of a world we have yet to even see.
For now, astronomers are racing to confirm the existence of Planet Nine.
If they succeed, we may finally have answers to some of the biggest mysteries of our cosmic neighborhood—but we may also have to come to terms with an unsettling truth: Planet Nine might not be the guardian of the outer Solar System, but rather, its executioner.
