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Mercury (Planet)

Mercury's Atmosphere

The mid-day surface temperature on Mercury rises to about 700K (803°F; 428°C), while the mid-nighttime temperature falls to 100K (-279.4°F; -173°C). This temperature variation, the largest experienced by any planet in the solar system, is due to the fact that Mercury has essentially no insulating atmosphere.

The main reason that Mercury does not have a distinctive atmosphere is that it is small and because it is close to the Sun. Mercury's small radius indicates that it has a low escape velocity, just 2.5 mi (4.2 km)/sec. Mariner 10 did detect a very thin atmosphere of hydrogen and helium on Mercury. It is believed, however, that Mercury's wispy atmosphere is composed of atoms that have been temporarily captured from the solar wind. Ground-based observations have found that a sodium and potassium atmosphere exists on the daylight side of Mercury. These atoms are probably released through the interaction of ultraviolet radiation with surface rocks.

Resources

Books

Beatty, J. Kelly, Carolyn Collins Petersen, and Andrew L. Chaikin. The New Solar System. Cambridge: Cambridge Univ. Press, 1999.

de Pater, Imke, and Jack J. Lissauer. Planetary Sciences Cambridge, UK: Cambridge University Press, 2001.

Morrison, D., and Tobias Owen. The Planetary System. 3rd ed. Addison-Wesley Publishing, 2002.

Taylor, F.W. The Cambridge Photographic Guide to the Planets. Cambridge University Press, 2002.

Periodicals

Strom, Robert. Mercury: The Elusive Planet. Washington, DC: Smithsonian Institution Press, 1987.

Strom, Robert. "Mercury: The Forgotten Planet." Sky & Telescope (September 1990): 256-60.

Other

Arnett, B. SEDS, University of Arizona. "The Nine Planets, a Multimedia Tour of the Solar System." November 6, 2002 [cited February 8, 2003]. <http://seds.lpl.arizona.edu/nineplanets/nineplanets/nineplanets.html>.

Martin Beech David T. King, Jr.

KEY TERMS

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Astronomical unit: —The average distance between the Sun and Earth. One astronomical unit, symbol AU, is equivalent to 92.9 million mi (149.6 million km).
Doppler effect: —The apparent change in the wavelength of a signal due to the relative motion between the source and observer.
Dynamo effect: —A model for the generation of planetary magnetic fields: The circulation of hot, conducting fluids within a planet's liquid core leads to the generation of a magnetic field.
Escape velocity: —The speed that an object must have in order to escape the gravitational pull of another body.
Lobate scarp: —A long, near vertical wall of rock running across a flat plain.
Mantle: —The outer layers of a planets interiorcore, usually composed of silicate rock.
Planetesimals: —Asteroid-sized bodies that accumulated to form protoplanets.
Solar wind: —A stream of charged and neutral particles that emanates from the Sun and moves into the solar system.
Synchronous rotation: —Any object that spins on its axis at the same rate that it moves along in its orbit is said to be in synchronous rotation. Also called to 1-to-1 spin-orbit coupling.

Additional topics

Science EncyclopediaScience & Philosophy: Mathematics to Methanal trimerMercury (Planet) - Basic Properties, Mercury's Rotation Rate, Surface Features, Polar Ice, Internal Structure