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The Vera Rubin Observatory, the most powerful telescope ever built, began its mission in Chile in June 2025 and may solve in the coming years the greatest mystery of modern astronomy: the existence of the ninth planet of the Solar System. Proposed in 2016 by astronomers from Caltech, the hypothetical planet would have ten times the mass of Earth and orbit the Sun at a distance 20 times greater than Neptune, taking up to 20,000 years to complete one orbit.
The ninth planet of the Solar System may be just a few years away from being found, and the tool that promises to reveal it is at the top of a mountain in northern Chile. The Vera Rubin Observatory, which began operations in June 2025, sweeps the entire sky of the southern hemisphere every few nights with unprecedented detection capability. Astronomer Sarah Greenstreet, a researcher at the observatory, states directly: “If Planet Nine exists at the hypothesized size and location, the Vera Rubin will find it.”
The hypothesis that there is a massive world hidden in the farthest regions of the Solar System has divided the scientific community since 2016. That year, astronomers Konstantin Batygin and Michael Brown from the California Institute of Technology (Caltech) published a paper arguing that a planet about ten times the mass of Earth orbits the Sun in a highly elliptical and inclined trajectory, far beyond Neptune. The evidence: a group of trans-Neptunian objects with orbits that are unusually elongated, which could only be explained by the gravitational influence of a giant neighbor.
What is Planet Nine and why do scientists believe it exists
According to information released by the portal G1, the hypothetical ninth planet would be larger than Earth but smaller than Neptune, a size that astronomer Malena Rice from Yale University highlights as the most common in other stellar systems. “We see this type of planet in about half of other stars, and we don’t have one within the Solar System”, notes Rice. The absence of a world in this size range in our system is, in itself, an anomaly that intrigues researchers.
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The main evidence for Planet Nine comes from the behavior of six distant trans-Neptunian objects, icy bodies that orbit the Sun beyond Neptune in the Kuiper Belt. Their orbits are unusually inclined and elongated, a pattern that computational models by Batygin and Brown can only reproduce with the presence of a massive celestial body exerting gravitational influence on them. Brown summarizes the situation: “If Planet Nine does not exist, we have no further explanations for many strange events.”
Why has no one been able to see Planet Nine until now
The main obstacle is distance. Caltech astronomers estimate that the ninth planet is, on average, 20 times farther from the Sun than Neptune, which means it could take up to 20,000 Earth years to complete a single orbit. An object so remote reflects very little sunlight, making it incredibly faint and practically invisible to conventional telescopes.
The predicted orbit further complicates the search. While the eight known planets travel around the Sun in nearly circular trajectories and in an approximately flat plane, the ninth planet would follow a highly elliptical and inclined orbit, meaning it may be in a region of the sky where no one has looked closely enough. Rice from Yale suspects that the planet may already be in existing data: “I am not at all convinced that it is not simply already in our data. We just need to look carefully.”
How the Vera Rubin Observatory can solve the mystery
The Vera Rubin represents a technological leap compared to previous telescopes. Installed in northern Chile, equipped with the largest digital camera ever built, the observatory does not focus on specific targets like James Webb, but systematically sweeps the entire southern hemisphere sky every few nights, cataloging billions of cosmic objects throughout its ten-year mission. It is expected to record more than 40,000 new trans-Neptunian objects.
The ability to find faint, distant objects is what sets the Vera Rubin apart from any previous instrument. “Rubin can find a large number of objects in space that are fainter and further away than we’ve ever been able to see before,” explains Greenstreet. Brown, from Caltech, believes the observatory “will either find Planet Nine directly or find virtually irrefutable evidence that it either exists or doesn’t exist” within a year or two.
Existing clues and the candidate found in 2024
In April 2024, a team of scientists from Taiwan, Japan, and Australia analyzed surveys from two infrared space telescopes launched in 1983 and 2006 and found a pair of corresponding faint spots that may represent an unknown planet moving over those 23 years. Lead author, Terry Phan, from National Tsing Hua University in Taiwan, is cautious and calls the finding “the discovery of a potential Planet Nine candidate,” not a confirmation.
The discovery was met with skepticism by the scientific community, but also with interest. If the spots detected in the infrared surveys do indeed correspond to the same object, it would be the first direct observation of the ninth planet, although it still requires independent confirmation. The Vera Rubin, operating continuously from Chile, is the ideal instrument to verify whether the candidate is real or if the spots are artifacts of old data.
Arguments against the existence of Planet Nine
Not all scientists are convinced. In 2023, the discovery of Ammonite, a trans-Neptunian object whose orbit does not align with those of the six TNOs originally analyzed by Batygin and Brown, weakened one of the pillars of the hypothesis. If the orbital pattern of distant objects is not as uniform as previously thought, the need for a massive planet to explain it diminishes.
In 2025, astrophysicists from the German institute Forschungszentrum Jülich presented computational simulations suggesting that the close passage of a massive star, billions of years ago, could have caused the gravitational chaos that altered the orbits of trans-Neptunian objects. Professor Susanne Pfalzner, who led the study, admits that Planet Nine may exist, but considers the probability low. If this theory is correct, Earth and its neighbors would have merely been spectators of a gravitational event that occurred billions of years ago. Greenstreet herself, from the Vera Rubin, acknowledges that “the evidence for this additional planet has diminished in recent years.”
What happens if the Vera Rubin doesn’t find the ninth planet
Even if the observatory’s images do not reveal Planet Nine, the mission is far from a failure. The vast region of the outer Solar System remains largely unexplored, and the data collected from Chile by the Vera Rubin may reveal objects and phenomena that no one even imagined. Brown, the astronomer who stripped Pluto of its planet status and now advocates for the existence of a new one, recognizes the irony of his position and the magnitude of what is at stake.
If the ninth planet is confirmed, it would be the first discovery of a planet in the Solar System in 180 years, since Neptune was formally identified in 1846. “Planet Nine would be the fifth largest in our Solar System and the first discovered in 180 years,” says Brown. If it is not found, the Vera Rubin’s data will still rewrite what we know about the Kuiper Belt and the boundaries of the system that Earth calls home.
Do you believe there’s a ninth planet hidden in the Solar System, or do you think scientists are chasing a mirage? Tell us in the comments what fascinates you more: the possibility of an unknown world orbiting the Sun for billions of years, or the technology of the telescope that might finally find it.
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