New discoveries of objects in the Kuiper Belt have also presented challenges for the Planet Nine theory. The latest is known ...

A new study suggests the existence of Planet Y. This hidden planet may be affecting the Kuiper Belt. The gravity of Planet Y could be causing a tilt in the orbits of some icy objects. Researchers ...

Planet Nine's composition is probably "most like Neptune," due to its distance from the sun, Brown said. "That would put its diameter at something like two times the width of Earth," he added.

If their calculations serve them correctly, Planet Nine would have a mass that is about 1.5 to 3 times that of Earth, at 500 times the distance between our home and the sun. Caltech researchers in ...

Planet Nine should be detectable by that telescope. But it would require an adjustment in the planned observing protocol to extend the telescope’s survey farther north than planned, Brown says ...

If Planet 9 is real, this observatory has around a 70 to 80 percent chance of finding it, he estimates, adding that it's not a sure thing because there are so many uncertainties.

Yet actually finding Planet Nine, sometimes called Planet X, has eluded scientists for nearly a decade. But the hunt for the solar system's potential ninth planet may soon be coming to a close.

And no, we're not talking about Pluto, which was demoted from full planetary status to "dwarf planet" in 2006. Instead, scientists believe Planet Nine is a gas or ice giant billions of miles ...

For years, astronomers have searched for evidence of a hidden giant planet at the edge of our solar system. New data suggests ...

Scientists have found evidence of a true ninth planet in our solar system. Nicknamed "Planet Nine," the real-life Planet X appears to have the mass of 10 Earths and is 20 times farther from the ...