In the study, Siraj and colleagues examine the possibility of an unseen planet in the far reaches of the Solar System, often called "Planet X." They explore whether unusual clustering patterns in the orbits of distant objects called trans-Neptunian objects (TNOs) could indicate the presence of such a planet. To investigate this, the authors focus on how TNOs with stable orbits (orbits unaffected by gravitational pulls from other planets) align in specific ways that could suggest they are influenced by a hidden planet.

The Search for Planet X

Interest in an additional planet beyond Neptune dates back over a century, with recent studies focusing on how TNOs orbit. Previous research has found that some TNOs’ orbits appear to cluster, which might suggest gravitational influence from an unseen body. However, debates about whether these clusters are real or are simply due to observation limitations have persisted. By using a larger dataset of 51 TNOs, including newly discovered ones, Siraj et al. aim to more definitively test for clustering in the angles of TNO orbits.

Testing Clustering in TNO Orbits

The authors perform tests to see if TNOs with stable orbits tend to cluster at a specific angle, known as the longitude of perihelion. They find evidence of clustering at a distance of about 170 AU (astronomical units) from the Sun, which suggests an unseen planet might be influencing these objects. For this analysis, they use advanced simulations, known as n-body simulations, to create models of TNO behavior under the influence of the known planets plus an additional hypothetical planet.

Simulating the Orbit of Planet X

Through 300 simulations, the study tests various possibilities for the mass, distance, and orbital shape of a hypothetical Planet X. The results suggest a planet around 4.4 times the mass of Earth, located approximately 290 AU from the Sun, with a somewhat elongated (or eccentric) orbit and a small inclination relative to the Solar System’s plane. This new model for Planet X contrasts with a previous model by Brown and Batygin, who suggested a slightly larger, more distant, and more inclined planet.

Ruling Out Other Explanations

The authors also consider whether observational biases might explain the clustering they observe. Since surveys are limited by factors like telescope visibility and TNO brightness, they conduct additional statistical tests to ensure that the clustering seen isn’t due to survey limitations. Results indicate that clustering in the longitude of perihelion is statistically significant and unlikely to be a result of observation alone.

Implications and Future Discoveries

If this unseen planet exists, it could potentially be detected by upcoming surveys, like the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST), which is expected to map much of the outer Solar System. LSST might even provide the first images of Planet X, as it will be capable of spotting distant objects down to the predicted brightness levels of this hypothetical planet.

Source: Siraj