Our planet is EARTH, a 5-letter word. EARTH is the third planet from the Sun and the only known planet to have life. It is the fifth largest planet in the Solar System and is composed of land, water, and air. EARTH's atmosphere is made up of nitrogen, oxygen, and other gases, which help to regulate the temperature and climate. The planet is home to millions of species of plants and animals, and its diverse ecosystems provide resources for humans.