Student Interest

The Hypothetical Planet Nine


In 2014, researchers first suggested the existence of a new planet in our solar system. The planet is commonly referred to as Planet Nine or Planet X—not to be confused with Pluto, a dwarf planet previously classified as the ninth planet. Planet Nine was theoretically proposed with the idea that its gravitational effects could explain the unusual clustering of orbits for a group of trans-Neptunian objects (TNO), objects like dwarf planets that orbit the sun at a greater average distance than Neptune (more than 250 times that of Earth). The alignments of a cluster of these TNOs may provide mathematical evidence to propose that a hidden planet may be guiding the orbits of these objects. It’s been suggested that the unseen planet would have a predicted mass of at least ten times the mass of Earth and an orbit 500 to 600 times as far from the Sun as Earth’s.


However, many astronomers have questioned the concept of the hypothetical planet, claiming that the clustering of the TNOs orbits is due to biases. Until this day, no observation of Planet Nine had been recorded. Recently, a new study published in the Planetary Science Journal suggests that this might all just be an illusion. The study analyzed 14 of the remote bodies and TNOs, showing no evidence of such clustering (Grossman, 2021). This discredits the most significant theory of Planet Nine’s existence. 


Gary Bernstein, an astronomer at the University of Pennsylvania, claims that the earlier studies that suggested the concept of Planet Nine “all relied on just a handful of objects that may not have represented everything that’s out there…The objects might have seemed to show up in certain parts of the sky only because that’s where astronomers happened to look” (Grossman, 2021). 


Astronomer Samantha Lawler of the University of Regina in Canada asserts that “the entire reason for it [Planet Nine’s theory] was the clustering of these orbits. If that clustering is not real, then there’s no reason to believe there is a giant planet in the distant solar system that we haven’t discovered yet” (Grossman, 2021). 


Although this new study seems to contradict the original theory, it does not entirely disregard it. Some remain optimistic about Planet Nine, claiming that the new study might be “strongly contaminated” by unstable objects. As of now, there’s no general consensus about the hypothetical planet. In order to prove its existence (or nonexistence), astronomers would need to discover and study more TNOs. 



Grossman, L. (2021, February 22). Signs of a hidden Planet Nine in the solar system may not hold up. Science News. 

NASA. (2019, December 19). Hypothetical Planet X. NASA Solar System Exploration.

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