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Does Mercury have an atmosphere?
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Mercury
Mercury as seen by the Messenger probe, January 14, 2008. This image shows half of the hemisphere missed by Mariner 10 in 1974–75 and was snapped by Messenger's Wide Angle Camera when it was about 27,000 km (17,000 miles) from the planet.
Mercury does not possess a significant atmosphere. Because the planet is small and experiences extreme heat, it lacks the gravity required to retain a substantial gaseous layer; its surface pressure is less than one-trillionth that of Earth.1
Instead of a traditional atmosphere, Mercury has a highly tenuous exosphere consisting of trace amounts of elements such as hydrogen, helium, oxygen, sodium, potassium, calcium, magnesium, and sulfur. These atoms are primarily derived from the solar wind or are ejected from the planet's surface soils by meteoroid impacts and solar bombardment. Due to the extreme thinness of this environment, Mercury lacks an ionosphere comparable to Earth's.12