NASA sent its probe New Horizons on a flyby in 2015. It confirmed the tiny planet harbored an ocean beneath its thick, icy shell. Pluto was always in a tough spot when it came to being a planet.

The surprising discovery of entities smaller than viruses raises profound questions about what life is and how it got started ...

On the 95th anniversary of its discovery, Pluto remains one of the most beloved and enigmatic worlds in our solar system, ...

The planet, if it is indeed a planet, is one of the most massive ever detected around a small star ... The planet is the fourth world to be spotted in data from the European Space Agency's ...