Scientists for years have sought a planet beyond the orbit of Neptune colloquially known as Planet 9 or Planet X
THE MESSENGER
The number of planets orbiting the Sun could soon again be nine. In a recent paper, researchers in Japan add to the evidence that there is another celestial body in the furthest corners of the solar system, a theoretical planet known colloquially as Planet 9 or Planet X.
For years, scientists have sought a planet beyond the orbit of Neptune, the furthest known planet from the Sun. (Pluto was downgraded to a dwarf planet in 2006.) The suspicion stems in part from observations and a lack of knowledge about the Kuiper Belt, a circle of icy celestial bodies beyond Neptune that is relatively unexplored and hard to observe from Earth.
The Kuiper Belt is known to be home to at least five dwarf planets, including Pluto, but in the new paper, the researchers use a mathematical model to predict whether a larger body might be in the Belt.
The models used data from several Kuiper Belt objects with orbits that don’t fit expected patterns, even after variables like the gravitational pull of Neptune or even other star systems are accounted for. A planet in the region, the researchers posit, could account for the weird orbits.
They then tested their theory for different-sized planets, finding that an Earth-like planet was the most likely culprit. Importantly, such a planet would be about the same size and mass as Earth — between 1.5 times and 3 times the size — but it is so far from the Sun that it would be ice.
The findings jibe with past research into Planet 9 and how it explains the ways in Kuiper Belt objects behave, but these findings typically theorize Planet 9 to be a super-Earth, a class of planets that are larger than ours but smaller than ice giants like Neptune and Uranus.
The new evidence is tantalizing, but the researchers acknowledge that further study of the Kuiper Belt is needed before it can be predicted where, exactly, Planet Nine may be relative to Earth. If researchers can glean this information, it may be possible to observe or even send a mission to find and study the planet, should it exist.
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