If Planet Nine exists, it’s taunting astronomers. Several studies of the orbits of small bodies far from the Sun hint at the presence of a massive planet in the outer solar system. Yet the possible world has remained hidden.

Planet Nine was suggested in 2014, based on the orbits of some big chunks of rock and ice beyond the orbit of Neptune, the Sun’s most-distant major planet. The orbits appear to be influenced by the gravity of a body many times as massive as Earth.

The most recent evidence of Planet Nine comes from a study that modeled the orbits of 29 objects beyond Neptune. All of the orbits are tilted and stretched out. At their closest, these objects pass just inside the orbit of Neptune, which is 30 times farther from the Sun than Earth is. But they average more than a hundred times the Earth-Sun distance, so it takes many centuries for them to orbit the Sun.

Astronomers calculated the likelihood of so many objects following similar paths under two scenarios. In one, they modeled the gravitational effects of the Sun’s known planets, plus the pull of the rest of the galaxy’s stars and gas clouds. In the other, they added the effects of a possible Planet Nine. The model with Planet Nine produced a far better match to the orbits.

So far, a search of observations made along the planet’s possible path has come up empty. So if Planet Nine exists, it’s playing a game of hide-and-seek far from the Sun.

Script by Damond Benningfield