Planet x

In January 2016, California Institute of Technology (Caltech) astronomers Konstantin Batygin and Mike Brown announced research that provided evidence for a planet about 1.5 times the size of Earth in the outer solar system. The existence of this distant world remains theoretical at this point. Batygin and Brown did not actually observe a planet. This hypothetical Neptune-sized planet would circle our Sun on a highly elongated path, far beyond Pluto. It could have a mass about 5 to 10 times that of Earth and orbit about 20 to 30 times farther from the Sun on average than Neptune. It would take between 10,000 and 20,000 Earth years to make one full orbit around the Sun. If it exists, this planet could help explain the unique orbits of some smaller objects in the distant Kuiper Belt, a region of icy debris that extends far beyond the orbit of Neptune. The existence of this far-off world rests on gravitational patterns in the outer solar system, and again — the planet remains theoretical at this point. Batygin and Brown nicknamed the hypothetical object “Planet Nine.” However, the notion of an undiscovered large planet in the realm beyond Neptune has been investigated multiple times in the past century, based on distinct lines of evidence. Sometimes it’s also referred to as “Planet X.” NASA does not take a position on the name used. The information on this page includes both names in the interest of helping the public to find it via online search. When was Planet X (Planet Nine) discovered? To be clear, Planet X (Planet Nine) has not yet been discovered, and there is debate in the scientific community about whether it exists.