Officially, the Solar System now has eight planets. Astronomers do not rule out, however, that large undiscovered bodies still remain in its distant reaches. The best-known candidate is the hypothetical Planet Nine, according to Evgeny Burmistrov, an expert in astronomy at Perm Polytechnic University.

Why Scientists Are Talking About New Planets at All

As more and more objects began to be found beyond Neptune's orbit, it became clear that the outer Solar System is far more complex than previously assumed. The discovery of the dwarf planet Eris and other large bodies in the early 2000s ultimately led to a revision of the very definition of a planet and to Pluto's demotion from "major" planet status in 2006.

In an interview with RIA Novosti, Burmistrov noted that new planets could well be added to the catalogue—we simply do not know about them yet. This refers to the detection of already existing objects, not the birth of new ones.

What Is Planet Nine

The most serious candidate for the status of an additional full-fledged planet remains the hypothetical Planet Nine. Its existence has not yet been confirmed by direct observation, but its presence is suggested by the orbital characteristics of certain very distant Kuiper Belt objects.

These bodies move along strange, distinctly clustered trajectories. Astronomers consider the gravitational influence of a large, as-yet-invisible object to be one possible explanation for this behaviour.

If Planet Nine does exist, its mass is estimated to be roughly five to ten times that of Earth. Such a body would take between 10,000 and 20,000 years to complete a single orbit around the Sun—meaning it lies extraordinarily far from us.

Why Has It Not Been Found Yet

Even a large planet at such a distance is extremely difficult to detect. It would be very dim, and its position in the sky can only be calculated approximately. Searches are continuing with the most powerful ground-based and space telescopes, but direct evidence remains elusive.

Nevertheless, the Planet Nine hypothesis remains one of the most debated topics in modern planetary astronomy. If the object is found, it will significantly change our understanding of the structure of the Solar System's outer regions.

In Brief

Astronomer Evgeny Burmistrov notes that new planets could theoretically be discovered in the Solar System. The leading candidate remains the hypothetical Planet Nine, with a mass of 5–10 Earth masses and an orbital period of 10,000–20,000 years. Its possible existence is indicated by the unusual clustering of orbits among distant Kuiper Belt objects. Direct proof is still lacking, but the search continues.