What do you call a mixture of gases and particles that surround a planet, held by gravity?

The mixture of gases and particles that surrounds a planet, held by gravity, is called an atmosphere. The atmosphere consists of various gases, including nitrogen, oxygen, carbon dioxide, and trace amounts of other gases, as well as water vapor and particulates. It plays a crucial role in supporting life by providing essential gases for respiration, protecting the planet from harmful solar radiation, and regulating temperature through the greenhouse effect. Each planet in our solar system has its own unique atmosphere, varying in composition and thickness. For example, Earth's atmosphere is quite different from that of Mars or Venus.