Where Is Planet Nine? Scientists Close in on the Mystery World's Probable Location in the Outer Solar System

Searching for planets around distant stars is comparatively straightforward, unlike the elusive Planet Nine, also called Planet X. The transit method, observing a star's light dip as a planet passes, has led to the discovery of thousands of exoplanets.

Scientists, in a decade-long quest, have now narrowed down Planet Nine's potential location, expressing confidence in finding it in the coming years after eliminating most of its theoretical orbital path.

Caltech's Pioneering Research on the Hypothetical Planet X

In January 2016, Caltech astronomers Konstantin Batygin and Mike Brown presented groundbreaking research suggesting a massive planet in the outer solar system. Based on complex mathematical models and simulations, it explained the unique paths of at least five smaller Kuiper Belt objects.

Jim Green, director of NASA's Planetary Science Division, expressed enthusiasm for the potential discovery while cautioning that it was premature to definitively label it as the elusive "Planet X." He emphasized that the announcement marked the inception of a scientific process driven by early predictions derived from limited observations.

The theorized Planet X, with a mass around ten times that of Earth, akin in size to Uranus or Neptune, was expected to orbit 20 times farther on average than Neptune, implying an orbital period of 10,000-20,000 years.

Further findings proposed by Brown, Batygin, and collaborators indicated its potential mass at seven times that of Earth, making it the solar system's fifth-largest planet, positioned 500-600 astronomical units from the sun.

Despite these advancements, uncertainties persist regarding its elliptical orbit, estimated to take between 5,000 and 10,000 years to complete, along with its likely slight tilt compared to known planetary orbits, leading to continued challenges in pinpointing its location in the ongoing quest for Planet Nine.

Seeking the Elusive Planet Nine

In a recent study, titled "A Pan-STARRS1 Search for Planet Nine" posted on the preprint database arXiv, researchers utilized data from the Pan-STARRS observatory in Hawaii to scrutinize 78% of Planet Nine's suspected orbital path. Covering 78% of the anticipated region, the analysis didn't reveal the elusive planet, with the remaining area beyond Pan-STARRS' current visibility.

Despite the absence of Planet Nine, these findings await peer review. Brown emphasized that ruling out most potential locations now requires a more challenging exploration of the farther regions. The team employed Pan-STARRS data, systematically examining Planet Nine's orbital route at monthly intervals, aiming to identify objects with monthly positional shifts.

This process, likened to a computationally intensive game of connecting the dots, faced challenges due to other celestial bodies, like asteroids and comets, exhibiting similar monthly changes.

To ensure accuracy, over 50,000 simulated Planet Nines were added to the data, with a high detection rate. The team estimates that Planet Nine likely occupies the most distant 22% of its proposed orbital pathway.

The researchers plan to advance the survey using data from the Subaru Telescope in Hawaii, covering inaccessible regions. If unsuccessful, the Vera C. Rubin Observatory, operational in 2025, may provide additional assistance in locating Planet Nine.