I.

Introduction

Extrasolar Planets, also exoplanets, planets orbiting stars other than the Sun. Astronomers have found more than 200 such planets. Billions of planets likely exist in our galaxy. Finding and studying extrasolar planets helps astronomers learn more about the formation of our solar system. It also contributes to the study of possible life in the universe, because life is more likely to develop on planets than in the extremes found on other bodies in space. See also Astronomy; Planetary Science; Star; Exobiology.