You’ve probably heard astronomers and members of the public argue about how many planets there are in our solar system. Ever since Pluto was downgraded from planetary status in 2006 and downgraded to “dwarf planet” status, people have argued that it should be reinstated. However, there is another debate about the number of planets in the solar system that is not so well known, namely whether there is a mysterious yet unobserved planet called Planet Nine.
Image: Caltech/R. Injured (IPAC)
The idea began with Caltech professors Mike Brown and Konstantin Batygin, who looked far into the solar system beyond the orbit of Pluto. This region, called the Kuiper Belt, is a disk of ice and debris that extends from Neptune’s orbit and is home to a number of dwarf planets.
The researchers found that the orbits of some of the bodies in this remote region, called Trans-Neptunian Objects (TNOs), seemed to cluster together in strange ways. They hypothesized that this grouping could be due to the presence of a giant planet too distant for us to observe it directly. They called their hypothetical object Planet Nine.
Since then, the idea of Planet Nine, also known as Planet X, has captured the imagination of many. There have been all sorts of theories about the object, including the idea that it could be even bigger and closer than previously thought (via Caltech) or that it could be a miniature black hole ( through arXiv).
These ideas are fun and engaging, though most astronomers treat the idea of Planet Nine with healthy skepticism. After all, we have never directly detected such a planet, and we only have circumstantial evidence to suggest that it exists.
However, even NASA is open to the possibility that Planet Nine could exist. The agency has a page on “hypothetical Planet X” stating that it could be 10 times the mass of Earth and could orbit so far apart that a year would be between 10,000 and 20,000 Earth years. But the experts he cites are careful to point out that the planet is just a theory at this point.
“The possibility of a new planet is certainly exciting to me as a planetary scientist and to all of us,” said Jim Green, director of NASA’s Planetary Science Division (via NASA). “This is not, however, the detection or discovery of a new planet. It is too early to say for sure that there is a so-called Planet X. What we are seeing is an early prediction based on modeling at from limited observations. This is the beginning of a process that could lead to an exciting result.
The originators of the theory, Brown and Batygin, continue their work to search for more clues about the real existence of another planet. “I would love to find it,” Brown said. “But I’d also be perfectly happy if someone else found it.” That’s why we publish this article. We hope other people will be inspired and start looking.