For years, astronomers have toyed with the idea that the Sun hides an extra planet so distant and dim that even the best ...

If the object really is Planet Nine, it would be larger than Neptune and exist 700 times further from the sun than Earth.

Astronomers have long speculated about an unseen planet lurking in the solar system's outer edge. This hypothetical world, ...

For over a century, astronomers have wondered if there's an extra planet in our Solar System that we haven't been able to see ...

including the dwarf planet Sedna, can be conveniently explained by the existence of a stealthy world pulling their gravitational strings. If there is a planet lurking out there, it should reflect ...

Several of those objects, including the dwarf planet Sedna, follow orbits that cluster in one sector of space instead of being spread evenly around the Sun. Computer simulations in 2016 showed ...