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The hidden Ninth Planet: A fact or an illusion?

Unraveling the universe’s countless mysteries while venturing into the realm of the unknown has always been a fascination of great minds. Moreover, understanding our solar system, as well as its planets, helps in our advancement. Thus, for a while, scientists believed in some evidence backing up the existence of a ninth planet on the edge of our solar system. However, new studies are now shedding the light on the uncertainty surrounding the ninth planet.

“We can’t rule it out,” says Kevin Napier, a physicist at the University of Michigan in Ann Arbor. “But there’s not necessarily a reason to rule it in.”

History of the ninth planet

In 2015, Caltech astronomers Konstantin Batygin and Mike Brown used mathematical modeling and computer simulations to provide evidence for the ninth planet’s existence, often known as “Planet X”. Though the prediction wasn’t based on direct observation, scientists theorized that the ninth planet was going through a unique, elongated orbit in the outer solar system. Furthermore, the planet’s existence would also serve as an explanation for the unusual orbits found in the distant Kuiper Belt.

Though the stimulation provided some convincing grounds for the planet’s existence, scientists still weren’t able to confirm the discovery. “The possibility of a new planet is certainly an exciting one for me as a planetary scientist and all of us,” said Jim Green, director of NASA’s Planetary Science Division. “This is not, however, the detection or discovery of a new planet. It’s too early to say with certainty there’s a so-called Planet X. What we’re seeing is an early prediction based on modeling from limited observations. It’s the start of a process that could lead to an exciting result.”

The planet’s description

Based on the calculated evidence, scientists think that planet X’s mass is almost 10 times that of Earth. Thus, its size is supposed to be similar to both Uranus or Neptune. Moreover, based on the theorized orbit, the ninth planet is about 20 times farther from our Sun. Thus, it would almost take between 10,000 and 20,000 years for the planet to finish one full orbit around the Sun.

Evidence against the planet’s existence

In the past, scientists observed the unusual movements of far-out objects. Said objects appear to be clustering as if an unseen giant planet is directing their movement. However, after analyzing 14 of the far-out objects, scientists didn’t find any form of clustering. Thus, the new study is shaking the basis of planet X’s theory. “It’s important to know what you couldn’t see, in addition to what you did see,” says Gary Bernstein, an astronomer at the University of Pennsylvania.

To further eliminate any uncertainty, Napier, Bernstein, and colleagues used the results of the Dark Energy Survey, the Outer Solar System Origins Survey, and the original survey run by Sheppard and Trujillo. Then, they conducted some computer simulations of almost 10 billion fake trans-Neptunian objects to determine whether the obtained positions would match the surveys’ predictions. Thus, the outcome was the same.

“It really looks like we just find things where we look,” Napier says. “Once you see where the lampposts really are, it becomes more clear that there is some serious selection bias going on with the discovery of these objects”. Thus, the chances of the objects being distributed randomly across the sky are the same as them being clumped up.

Hope remains for the planet X

Though the evidence is now less convincing, planet nine might still exist. “People have been very into saying that this kills Planet Nine,” Napier says. “I want to be very careful to mention that this does not kill Planet Nine. But it’s not good for Planet Nine.”

Planet nine can still provide a logical explanation for many of the solar system’s other mysteries. Therefore, Batygin, an astronomer and Associate Professor of Planetary Sciences at Caltech, still believes in the existence of planet nine. “I’m still quite optimistic about Planet Nine,” he says. He then compares the analysis to finding bears east of the forest and assuming the existence of a bear cave. “But Napier is saying the bears are all around us because we haven’t checked everywhere,” Batygin says. “That logical jump is not one you can make.”


Crane, L. (2021). Evidence for a hidden ‘Planet Nine’ beyond Neptune has weakened. New Scientist., Z. (n.d.). If Planet Nine exists, why has no one seen it? BBC Future. Retrieved February 25, 2021, from X. (n.d.). NASA Solar System Exploration. Retrieved February 25, 2021, from, H. (2021, February 22). Signs of a hidden Planet Nine in the solar system may not hold up. Science News.