Planet 9: New evidence for the existence of an unknown large body in the Solar System

New study based on mathematical models offers the “strongest statistical evidence to date” for the existence of a large, unknown planet beyond the orbit of Neptune.

The idea of ​​a hypothetical “Planet 9” has been circulating since 2015, when a team at the California Institute of Technology (Caltech) spotted a number of bodies moving as a group beyond the orbit of Pluto, near the edge of the Solar System.

They then hypothesized that the objects clustered together due to the gravitational pull of an unknown planet.

The new study, co-authored by Caltech researchers themselves, now appears to reinforce suspicions.

Discovering planets

But how is it that an entire planet is hiding in our cosmic neighborhood, while astronomers are discovering thousands of planets orbiting distant stars?

Planets outside the Solar System, known as exoplanets, are generally easier to spot, either because they block some of their star’s light as they pass in front of it, or because they cause wobbles in the star’s motion due to their gravitational pull.

Two techniques are used to discover bodies in the Solar System: either their direct observation in the sky, or the detection of disturbances in the motion of other bodies due to gravitational interaction.

Seven of the eight planets in the Solar System were discovered using the first method. The only exception is Neptune, which was discovered thanks to the French mathematician Urbain Leverier, who noticed that the orbit of the planet Uranus was different from what Newtonian physics predicted. He then assumed that the discrepancy was due to the presence of an unknown planet and predicted their position.

Simulations

In the new study, the researchers looked at distant objects that cross Neptune’s orbit and do not approach the Sun within 15-30 astronomical units (AU), where one AU equals the Earth-Sun distance, about 150 million kilometers.

The available data were fed into computer models with which a series of simulations were carried out. The analysis took into account the gravitational influence of stars passing in front of the Sun, and even the so-called “galactic tide”, as the gravitational influence of bodies beyond the Solar System is known.

The simulations that best explain the behavior of the objects in question are those that include a distant but large planet, the team reports in a study accepted for publication in the Astrophysical Journal Letters and available as a pre-publication in the ArXiv repository.

However, the analysis does not indicate where such a body might be hiding. The researchers also clarify that there are alternative explanations that cannot yet be ruled out.

They point out, however, that Planet 9, if it exists, could be detected by the Vera Rubin Observatory being built in Chile and expected to be operational in 2015.