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Mercury's thin atmosphere contains hydrogen, helium, and oxygen. It also has smaller amounts of sodium, potassium, calcium, and magnesium. This picture shows sodium near Mercury. Red and green areas have the most sodium.
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Image courtesy of NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.

Atmosphere of Mercury

Mercury has almost no atmosphere. The planet's small size means that its gravity is too weak to hold down a normal atmosphere. There is a very thin atmosphere around the planet. Mercury's thin atmosphere is constantly being "blown away" into space by the pressure of sunlight and by the solar wind. Gases are constantly being added to Mercury's atmosphere, too. That's why it still has any atmosphere at all - even though that atmosphere is really, really thin.

Mercury's atmosphere contains small amounts of hydrogen, helium, oxygen, sodium, potassium, calcium, and magnesium. Some of the gas particles come from the solar wind. Others are made by radioactive decay or when micrometeorites smash into the surface. All of these gases are soon carried away from Mercury by the solar wind and by Mercury's magnetic field. Atmospheric pressure at the planet's surface is less than one trillionth of Earth's (around one nanopascal or 10-14 bar).

Temperatures at the surface range between 100 and 700 kelvins (-280° F to 800° F or -173° C to 427° C). Lead melts at 600 kelvins! This large range in surface temperature is possible because Mercury is so close to the Sun (a year is only 88 Earth days long) and does not have enough atmosphere present to moderate the range in surface temperature.

Last modified August 11, 2010 by Randy Russell.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA