What is the best definition of an atmosphere as used in the article "New NASA Rover Lands on Mars with a Helicopter"? An atmosphere is the general tone or mood of a place, situation, or work of art. An atmosphere is the general tone or mood of a place, situation, or work of art. Our atmosphere has the right combination of nitrogen and oxygen gases needed for humans to breathe. Our atmosphere has the right combination of nitrogen and oxygen gases needed for humans to breathe. An atmosphere is the layer of gases that surrounds a planet. An atmosphere is the layer of gases that surrounds a planet. Without the atmosphere there could be no life on Earth. Without the atmosphere there could be no life on Earth.