The study ‘Is There an Earth-like Planet in the Distant Kuiper Belt?‘ suggests that a thus far undetected Earth-like planet hovering in the Kuiper Belt region could be deviating orbits of Sedna and a handful of similar trans-Neptunian objects (TNOs), which are the countless icy bodies orbiting the sun at gigantic distances.

Many TNOs have oddly inclined and egg-shaped orbits, possibly due to being tugged at by a hidden planet, astronomers say. Two Japanese researchers used computer simulations to analyze the effects of such an undiscovered planet on the TNOs. Those simulations, which included evolutions of numerous real and model TNOs in the furthest reaches of an icy region, known as the Kuiper Belt, produced the extreme orbits observed for Sedna and other TNOs. Such a planet would be between 1.5 to three times Earth’s size and would reside somewhere between 37 billion km to 74 billion km from the sun.

Searching for planets lurking in the frigid edges of our solar system is not a new concept. The so-called Planet Nine, a world 10 times more massive than Earth, is thought to be responsible for at least five strange features in the solar system including the oddly inclined orbits of a few Kuiper Belt objects. This theoretical orb has captured the attention of many, but remains undetected. But research suggests if Planet Nine exists out there, it could be residing somewhere between 59 billion km to 119 billion km from the sun.

Although the possibility of Planet Nine gained significant traction from research groups worldwide, the theory has also been controversial. Some astronomers argue that the highly eccentric orbits of TNOs, for which Planet Nine’s presence was considered necessary, could occur without the hidden planet’s presence. In 2021, an independent study in fact claimed data used by the team behind the discovery paper first theorizing Planet Nine was biased, and concluded that there’s a very low chance of such a planet existing. In comparison to Planet Nine, the newly hypothesized planet — dubbed “Kuiper Belt Planet (KBP)” — would be much closer and more influential on the orbits of Kuiper Belt’s objects, especially those beyond 7 billion km, according to the study.