New research suggests the moons of Jupiter and Uranus may hint that our planetary neighborhood once had a third ice giant.

The history of Earth is written on the great tablets of tectonic plates. The motions of plates shaped land masses, formed oceans, and created the varied climates and habitats that set the stage for ...

If you were to imagine all of Earth's history as just one day, as in Carl Sagan's cosmic calendar, humans wouldn't arrive until the last few seconds before midnight. A few hundred thousand years of ...

For centuries our solar system was the only planetary system known to humans. We had no proof other worlds existed beyond those in our own cosmic backyard, and we imagined that if other planetary ...

As J.R.R. Tolkien wrote in The Fellowship of the Ring, “Not all those who wander are lost.” But in the case of planets, it’s possible that most of them are. Rogue planets—planets that are adrift in ...