For years, astronomers have speculated about a mysterious ninth planet lurking in our Solar System. Unlike Pluto, this hypothetical “Planet Nine” is far beyond Neptune, remains unconfirmed, and might not even be a traditional planet. Some theories suggest it could be a small black hole or composed of dark matter. Its existence is inferred from anomalies in the orbits of Trans-Neptunian Objects (TNOs)—Pluto-sized bodies in the Kuiper Belt.

Now, a new preprint proposes a fresh way to find Planet Nine by searching for moons it may have captured. These moons, formed by smaller TNOs trapped in Planet Nine’s gravitational pull, could provide indirect evidence of the planet’s presence. Despite their small size and distance, these moons might emit detectable heat due to a phenomenon called tidal heating.

Tidal heating occurs when the gravitational interaction between a planet and its moon creates friction inside the moon. This happens because the gravitational pull is stronger on the closer side of the moon, distorting it into a slightly elongated shape. As the moon orbits, this deformation shifts, causing internal friction that generates heat.

While Planet Nine itself might not emit detectable signals like light or heat, its moons could produce faint heat from tidal forces. This heat, though minimal, could theoretically be detected by telescopes, offering a way to locate the elusive planet. The method resembles how astronomers study black holes by observing the light and heat produced by matter around them.

The theory remains speculative, but it offers a promising lead. If Planet Nine exists, it could be five to ten times the mass of Earth and explain the peculiar behavior of distant Kuiper Belt objects. Alternatively, if it is a black hole or a dark matter object, detecting its moons might still be feasible using this approach.

The search for Planet Nine continues to push the boundaries of astronomical research, blending innovative ideas with established techniques. Whether through tidal heating or other methods, finding this mysterious object would provide profound insights into the dynamics and composition of our Solar System.