Back in January, a study pointed to evidence of Planet Nine, a hypothetical planet located past Pluto. A month later, another research team narrowed down the area where they believed the planet was located, bringing scientists closer to being able to confirm or deny its existence. Although no conclusive evidence has surfaced thus far, various teams have been conducted their own studies into the possible ninth planet.
One of these recent studies, conducted by scientists at the University of Arizona, found that the high eccentricity of distant Kuiper Belt Objects (KBOs) could mean that they crossed paths with a massive planet years ago.
Back when the initial proposition of Planet Nine was announced, the team revealed that KBOs were highly clustered with respect to their perihelion positions and orbital planes, also indicating that their calculations revealed that these findings were not likely chance. This lead the team to theorize that a distant eccentric planet - over ten times as massive as the Earth - was responsible for maintaining these orbits.
A recent paper proposed an alternative explanation: if Planet Nine was crossing paths with high-eccentricity KBOs, it's likely that its orbit was in resonance with them.
"The extreme Kuiper belt objects we investigate in our paper are distinct from the others because they all have very distant, very elliptical orbits, but their closest approach to the Sun isn't really close enough for them to meaningfully interact with Neptune," the researchers said. "So we have these six observed objects whose orbits are currently fairly unaffected by the known planets in our Solar System. But if there's another, as yet unobserved planet located a few hundred AU from the Sun, these six objects would be affected by that planet."
In their analysis of the KBOs, the team reveals that the resonances observed are simply not likely without the presence of a larger planet in our solar system, leading some to believe that this could be Planet Nine.
"For a resonance to be dynamically meaningful in the outer Solar System, you need one of the objects to have enough mass to have a reasonably strong gravitational effect on the other," the team added. "The extreme Kuiper belt objects aren't really massive enough to be in resonances with each other, but the fact that their orbital periods fall along simple ratios might mean that they each are in resonance with a massive, unseen object."
Further observations and calculations will need to be conducted before confirming the Planet Nine explanation.
