A planetary atmosphere is a layer of gases surrounding a planet, held in place by the planet's gravity. These gases can include nitrogen, oxygen, carbon dioxide, and other elements, depending on the planet. The atmosphere plays a crucial role in regulating temperature, protecting the surface from harmful radiation, and supporting weather patterns. Different planets have varying atmospheres. For example, Earth has a breathable atmosphere rich in oxygen, while Mars has a thin atmosphere mostly composed of carbon dioxide. Venus has a thick atmosphere that creates a strong greenhouse effect, leading to extremely high surface temperatures.