An exoplanet is any planet beyond our solar system. Most orbit other stars, but some free-floating exoplanets, called rogue planets, drift through the galaxy untethered to any star. We've confirmed more than 6,000 exoplanets out of the billions we believe exist.

Most discovered exoplanets are in a relatively small region of our galaxy, the Milky Way. Even the closest known exoplanet, Proxima Centauri b, is still about 4 light-years away. Scientists now know there are more planets than stars in the galaxy.

By measuring exoplanets' sizes and masses, we can determine compositions ranging from rocky (like Earth) to gas-rich (like Jupiter). We've identified lava worlds covered in molten seas, puffy planets with the density of Styrofoam, and super-Earths that might harbor conditions suitable for life.