Could an 'Earth-like' planet be hiding in our outer solar system?

Among the many mysteries that make the furthest reaches of our solar system, well, mysterious, is the exceptionally egg-shaped path of a dwarf planet called 90377 Sedna.

Its 11,400-year orbit, one of the longest of any resident of the solar system, ushers the dwarf planet to seven billion miles from the sun, then escorts it out of the solar system and way past the Kuiper Belt to 87 billion miles, and finally takes it within a loose shell of icy objects known as the Oort cloud.

Since Sedna's discovery in 2003, astronomers have struggled to explain how such a world could have formed in a seemingly empty region of space, where it is too far to be influenced by giant planets of the solar system and even the Milky Way galaxy itself.

Now, a new study suggests that a thus far undetected Earth-like planet hovering in that region could be deviating orbits of Sedna and a handful of similar trans-Neptunian objects, which are the countless icy bodies orbiting the sun at gigantic distances.

Two Japanese researchers used computer simulations to analyze the effects of such an undiscovered planet on the TNOs.

Such a planet would be between 1.5 to three times Earth's size and would reside somewhere between 23 billion miles to 46 billion miles from the sun, astronomers say.

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.

Research suggests if Planet Nine exists out there, it could be residing somewhere between 37 billion miles to 74 billion miles from the sun.

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" – would be much closer and more influential on the orbits of Kuiper Belt's objects, especially those beyond 4 billion miles, according to the new study.