Halley’s Comet, one of the most famous comets, has a very thin atmosphere. When the comet approaches the Sun, it heats up and releases gas and dust, creating a bright coma and a tail. This atmosphere, or coma, primarily consists of water vapor, carbon dioxide, carbon monoxide, and other hydrocarbons.
The gases escape from the surface of the nucleus of the comet as it sublimates due to the Sun’s heat. However, this atmosphere is not like the air we breathe on Earth; it is incredibly sparse and does not support life. The pressure in Halley’s Comet’s atmosphere is less than one millionth of Earth’s atmospheric pressure.
In summary, while Halley’s Comet does have an atmosphere created when it approaches the Sun, it is extremely thin and composed mostly of gases released from the comet’s surface, vastly different from Earth’s breathable atmosphere.