We already know that the solar system is more complicated than we thought, especially with the revelation of Planet Nine potentially out there. And if that weren’t enough, it turns out a planet the size of Mars might be lurking much closer to Earth.
Researchers at the University of Arizona have been studying the Kuiper Belt, basically a giant ring of space trash circling the very edge of the solar system, and they’ve noticed something odd. See, all the stuff circling a solar system tends to settle to a certain angle, what’s called “the invariable plane.” Basically the solar system asserts just enough gravity to keep this stuff (space rocks) under control, provided nobody in the nearby neighborhood has a stronger gravity.
But, at the far edge of the belt, the rocks aren’t doing that. Instead, they’re about eight degrees off. And the most logical explanation, although the team is careful to offer a few others — a star buzzing our solar system millennia before — is that there’s a “planetary mass object,” somewhere between the size of Earth and Mars sitting out there. And it’s much closer than Planet Nine.
We haven’t seen it yet, of course, and that might be tricky. Technically, we’re 63 degrees off from the overall plane of the galaxy, so for us all the junk in the universe sits on the same shelf, making it hard to spot stuff at a distance. Also, it’s technically not a planet because it hasn’t driven away all the space junk, so astronomers haven’t been looking for it. But the conclusions are compelling, and the hunt for this object, planet or not, is on.