The Internet is full of conspiracy theories about how undiscovered planets are just waiting to crash into Earth. The evidence suggesting the existence of a new planet, dubbed Planet Nine, has fueled these “truthers” that Nibiru or Planet X or Nemesis is real and it’s coming for us.

In reality, if Planet Nine exists it is far beyond the orbit of Neptune and not really affecting us. But, according to a new study, Planet Nine will eventually cause a lot of disarray in the Solar System, though only when the Sun is at the end of its life.

Dr Dimiti Veras from the University of Warwick has simulated the evolution of the Solar System in the distant future. The Sun will start to die in about 7 billion years, and towards the end of its life, it will turn into a red giant, becoming so large it could even reach, and possibly consume, Earth.

The outer layers of such a large star are not tightly bound by gravity, so the gas is slowly blown out in a mass ejection, turning the Sun into a white dwarf. The mass ejection will also push the system’s gas giants Jupiter, Saturn, Uranus, and Neptune outwards, reaching a safe orbital distance. It's almost a fairy tale ending for them.

But in every good fairy tale you need a dangerous uninvited guest, and in Veras’ research, the “villain” is Planet Nine. The simulation indicates that when the orbits of the gas giants stretch out, the influence of Planet Nine becomes important, and it could lead to a cosmic billiard ball match. Depending on the mass of Planet Nine and where the gas giants end up, the gravitational influence of the mysterious new planet could rip Uranus and Neptune away or push them towards the Sun. 

“The existence of a distant massive planet could fundamentally change the fate of the Solar System. Uranus and Neptune, in particular, may no longer be safe from the death throes of the Sun,” said Veras in a statement.

“The fate of the Solar System would depend on the mass and orbital properties of Planet Nine, if it exists.”

In a paper, published in the Monthly Notices of the Royal Astronomical Society, Veras links this potential scenario with white dwarfs across the Milky Way. White dwarfs are often observed surrounded by rocky debris clouds, so maybe those systems had a Planet Nine of their own.