Planet Nine

Epic card · No. 12930

Planet Nine is a hypothetical ninth planet in the outer region of the Solar System. Its gravitational effects could explain the peculiar clustering of orbits for a group of extreme trans-Neptunian objects (ETNOs)—bodies beyond Neptune that orbit the Sun at distances averaging more than 250 astronomical units (AU). These ETNOs tend to make their closest approaches to the Sun in one sector, and their orbits are similarly tilted. These alignments suggest that an undiscovered planet may be shepherding the orbits of the most distant known Solar System objects. Nonetheless, some astronomers question this conclusion and instead assert that the clustering of the ETNOs' orbits is due to observational biases stemming from the difficulty of discovering and tracking these objects during much of the year. Based on earlier considerations, this hypothetical super-Earth-to-mini-Neptune sized planet would have had a predicted mass of five to ten times that of the Earth, and an elongated orbit 400–800 AU...

Read on Wikipedia · Image nagualdesign; Tom Ruen, background taken from File:ESO - Milky Way.jpg, CC BY-SA 4.0