Jul 22, 2018 I Paul Seaburn

Planet X May Actually Be a Rogue Star

Planet X or Nine or 9 is:
a) a giant planet
b) a cluster of asteroids
c) a myth
d) none of the above
e) all of the above

If you said “none of the above,” Germany’s Max Planck Institute of Radio Astronomy thanks you for your support. This week it issued a paper supporting the idea that a violent restructuring of our solar system some time soon after its formation may have been caused by something completely different.

“The study presented shows that a close fly-by of a neighbouring star can simultaneously lead to the observed lower mass density outside [the solar system] and excite trans Neptune objects onto eccentric, inclined orbits.”

New Scientist announced the study with an interview of Max Planck astronomer Susanne Pfalzner. She led a team investigating the strange orbits of trans-Neptunian objects, particularly the dwarf planet Sedna, one of the most distant object to orbit our Sun, completing the huge oblong loop once every 11,400 Earth years. Sedna is the largest of at least 20 trans-Neptunian objects with these long, misshapen orbits that have puzzled astronomers since their discovery. Adding to the confusion is the Kuiper Belt, a region also beyond Neptune made of tiny, icy comets, asteroids and other small bodies.

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Artist's conception of Sedna

With no visible cause of this trans-Neptunian chaos, astronomers turn to models to speculate on possible causes. That – not the warnings of Planet X or Nibiru doomsday predictors – is how the idea of a large ten-times-the-mass-of-Earth Planet 9 developed in 2015. Besides the fact that it doesn’t explain everything, including how a planet that big could travel so far away from the Sun that we can’t find it, prompted Pfalzner’s team to try modeling a close encounter with a rogue star.

The simulations showed a one-in-four chance of a rogue star passing close by during a billion year period early in the life of the solar system. And by “close, they mean really close – 80 to 100 astronomical units (80 to 100 times the distance between Earth and the Sun). Sedna, the result of this possible brush-by, is 86 AU away from the Sun at its closest point. A star that close to the Sun would “excite” any and all things nearby, pulling tiny objects into the Kuiper Belt and knocking larger ones like Sedna into strange orbits.

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Orbits of Sedna, other objects and a possible orbit of Planet X

Then there’s Planet 9. Pfalzner’s models do not refute the existence of Planet 9 but they change its size. The simulations worked best when Planet 9 was the size of the Earth. That would allow it to be in a long oblong orbit and keep it small enough that it’s still a needle in the galactic haystack to detect.

So, does the probability of a rogue star stirring up the solar system also answer the question of what is Planet X? Of course not. It doesn’t even answer the question of what to call it. Instead, it keeps the mystery planet in play, albeit a fraction of its former size.

Should we now call it Planet 1/X?

Paul Seaburn

Paul Seaburn is the editor at Mysterious Universe and its most prolific writer. He’s written for TV shows such as "The Tonight Show", "Politically Incorrect" and an award-winning children’s program. He's been published in “The New York Times" and "Huffington Post” and has co-authored numerous collections of trivia, puzzles and humor. His “What in the World!” podcast is a fun look at the latest weird and paranormal news, strange sports stories and odd trivia. Paul likes to add a bit of humor to each MU post he crafts. After all, the mysterious doesn't always have to be serious.

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