Add Yahoo as a preferred source to see more of our stories on Google. When you buy through links on our articles, Future and its syndication partners may earn a commission. An illustration of ...

This video explains how the number of planets in our solar system depends on how we define a “planet.” The International Astronomical Union established three criteria, including clearing an orbit, ...

An exoplanet is what we call planets that exist outside of our own solar system. The first one was discovered in 1992, but as we get more powerful and precise telescopes and instruments, scientists ...