The number of planets that orbit the sun depends on what you mean by “planet,” and that’s not so easy to define ...

There may be an undiscovered planet in the outer solar system whose presence is revealed by the strange orbit of objects beyond the eighth planet Neptune. The tantalizing prospect of a ninth ...

No one was able to observe the planet directly ... James Unwin: If we do do our searches and it turns out that there is a planet in the outer solar system, this would be an absolutely incredible ...

This is a montage of Hubble Space Telescope views of our solar system's four giant outer planets: Jupiter, Saturn, Uranus, and Neptune, each shown in enhanced color. The images were taken over ...

Brown is still busy investigating the outer solar system ... you admit the possibility of a Planet 9, and you think about how Planet 9 got there, there’s no reason to not start asking the ...