01 January 2026, 07:03

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Dr. Stamatellos – What does he say about the possible fall of the unknown planet

Dr. Stamatellos – What does he say about the possible fall of the unknown planet

Planet X isn't "dead" yet, but the evidence for its existence is weakening, Dr. Dimitris Stamatellos, Associate Professor at the University of Lancashire, United Kingdom, regarding the question of whether there is another planet in our solar system, the unknown planet 'X'.

Which planets do we already know?

As is well known, since ancient times the world knew of the existence of the five planets visible to the naked eye — Mercury, Venus, Mars, Jupiter and Saturn. Two more, Uranus and Neptune, were added to the list of planets about 200 years ago thanks to the use of telescopes.

But the question remains: Are there other planets in our solar system?

The recent discovery casts doubt on the hypothesis of the existence of Planet 'X'. The farther a planet is from the Sun, the harder it is to observe, even with the most powerful telescopes. Distant planets receive little sunlight, making them dim and difficult to detect.

Is Pluto the ninth planet?

Pluto was once considered the ninth planet, but lost that status because it is not large enough to clear its orbit of the debris-remnants of the material that gave birth to the planets.

What are these little phenomena?

Such solar system bodies are now referred to as dwarf planets. An increasing number of them have been discovered in orbits further from Neptune's orbit, and are known as Post-Neptune Objects,

The Post-Neptunian Objects and Planet 'X'?

Interestingly, several of the Post-Neptunian Objects seem to cluster in a particular region of the sky. This unusual pattern has led some scientists to hypothesize the existence of an unknown planet, sometimes larger than Earth, nicknamed Planet X, whose gravity may explain this concentration. This idea, proposed in 2016, has reignited excitement in the planetary scientific community and attracted much attention in both academia and the media.

Since then, he said, astronomers have been searching for Planet X, but without success.

It's a difficult undertaking: the region of sky to be surveyed is vast, and such a planet would be extremely faint. If it exists, Planet X is hundreds of times farther from the Sun than Earth is. In addition, its orbit may be inclined or elliptical, hiding it in regions of the sky that have not yet been fully explored. So far, observational research has not yielded any results.

What is the most recent discovery and what are the doubts about the Planet X case?

The recent discovery of a new Post-Neptunian Object, 2017 OF201, has cast doubt on the Planet X hypothesis. This object is located approximately in the region where Planet X is predicted to exist. If such a large planet existed, it would destabilize the orbit of 2017 OF201, perhaps even displacing it from the Solar System. Its presence therefore indicates that the observed concentration of Post-Nepsidonian Objects may not require the existence of an unknown planet.

What scientists how should they work?

Caution is required. The orbit of 2017 OF201 is currently only roughly known, and more observations are needed to confirm its characteristics. In addition, other Post-Neptunian Objects need to be discovered to explain the observed concentration.

Astronomers can't see accurately?

Orbital uncertainties are large for such distant objects, since astronomers can only observe a small fraction of their orbits, which span thousands of years. More observations over time will help to better understand their properties.

Does this new finding mean that it does not completely rule out the existence of Planet X?

It is possible that the observed concentration of PNOs has been misinterpreted, as a result of the small number of bodies observed. Statistical biases in the analysis of observations can sometimes create apparent patterns that do not prove true when more observations are made. As we continue to discover more Post-Neptunian Objects through new surveys, such as the one being conducted by the upcoming Vera Rubin Observatory in Chile, we will get a clearer picture.

What can we expect from the Vera Rubin Observatory's "Legacy Survey of Space and Time" (LSST)?

It is expected to revolutionize our understanding of the outer regions of the solar system by detecting thousands of new Post-Neptunian Objects. If a few more bodies similar to 2017 OF201 are discovered, then the Planet X theory will receive a major blow. But if new bodies are found that support the initial clustering, then interest in Planet X may be rekindled."

For Mr. Stamatello, "Planet 'X' is not yet "dead", but the evidence for its existence is weakening. As in many areas of science, the answer may not come from a single discovery, but from the gradual accumulation of data and their careful interpretation. Until then, the search continues.

"A few years ago I predicted that if Planet X existed, it would have been discovered within two years. The recent negative discovery confirms my prediction. I don't really want to close the door on a new planet, but maybe it's time to forget about it."

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