The third planet from the Sun and the largest of the four inner, or terrestrial, planets. The Sun is an average-sized, middle-aged star situated toward the outer edge of one of the spiral arms of the Milky Way Galaxy. So far as is known, Earth is unique in the solar system in having life. Whether life exists in the universe beyond the solar system is unknown. However, recent discoveries have proven that there are planets in orbit around many nearby stars, so there are possibly billions of Earth-like planets in the universe where life may yet be discovered.