A mysterious planet — called Planet 9 or Planet X — may be hiding at the edge of our solar system. Will we ever find this world?
Planet nine may be orbiting far from the Sun, at the edge of our solar system. Astronomers, seeing odd irregularities in the orbits of the outer planets suspect another, unknown, planet may orbit beyond the eight we know of today.
The number of known planets in our solar system has risen and fallen over time. From the six worlds known to ancient people (including Earth), astronomers have found the planets Uranus and Neptune.
Uranus was first seen in 1781, and seventy years later, astronomer Giuseppe Piazzi announced his discovery of an “eighth planet,” orbiting between Mars and Jupiter. This object, Ceres, was found to the largest member of the main asteroid belt, and was classified as such in 1851. At that point, the solar system was said to contain 13 planets (including Neptune, first seen in 1846), and the number of recognized planets was reduced to just eight members.
[Read: The oceans of Jupiter’s moon Europa may be habitable, according to NASA]
In 1930, Clyde Tombaugh found Pluto, known for decades as the 9th planet. This distinction lasted until 2006, when Pluto was “demoted” to the class of dwarf planets. However, Ceres was also named to this group, recognizing its unique characteristics.
Despite its classification of Pluto as a dwarf planet, it is now recognized as the first Trans-Neptunian Object (TNO), and the first member of the Kuiper Belt, ever found. Today, we know of many minor bodies beyond Neptune — 316 were recently discovered in just a single study.