The solar system has another planet, but where is it hiding?

20 September 2023

Astronomers are convinced the solar system hosts another planet, often dubbed Planet Nine, or Planet X, but are unable to agree on its size and mass, nor its location.

A few years ago speculation was rife a Neptune size body was orbiting the Sun well beyond Pluto, taking between ten to twenty thousand years to make a circuit. While mathematical evidence suggested the existence of the planet, observations turned up nothing.

Now astronomers think a planet similar in size to Earth may be lurking in the far reaches of the solar system, though nowhere as far out as the supposed Neptune size body:

According to planetary scientists Patryk Sofia Lykawka of Kindai University in Japan and Takashi Ito of the National Astronomical Observatory of Japan, this world, frozen and dark so far from the Sun, would be no greater than 3 times the mass of Earth, and no farther than 500 astronomical units from the Sun.