Further Reading

Kusky, Timothy M., and Dwight C. Bradley. "Kinematics of Mélange Fabrics: Examples and Applications from the McHugh Complex, Kenai Peninsula, Alaska." Journal of Structural Geology 21, no. 12 (1999): 1,773-1,796.

Raymond, Loren, ed. Mélanges: Their Nature, Origin, and Significance. Boulder, Colo.: Geological Society of America Special Paper 198, 1984.

Mercury The closest planet to the Sun, Mercury, is an astronomical midget. This planet has a mass of only 5.5 percent of the Earth's, a diameter of 3,031 miles (4,878 km), and an average density of 5.4 grams per cubic centimeter. Mercury rotates once on its axis every 59 Earth days and orbits the Sun once every 88 days at a distance of 36 million miles (58 million km). Because it is so close to the Sun, one cannot see it with only the naked eye unless the sun is blotted out, such as just before dawn, after sunset, or during total solar eclipses.

Mercury has such a weak gravitational field that it lacks an atmosphere, although bombardment by the solar wind releases some sodium and potassium atoms from surface rocks, and these may rest temporarily near the planet's surface. The magnetic field is very weak, approximately 1/100th as strong as Earth's. The surface of Mercury is heavily cratered and looks much like the Earth's Moon, showing no evidence for ever having sustained water, dust

Image mosaic of Mercury. After passing on the dark side of the planet, Mariner 10 photographed the other, somewhat more illuminated hemisphere of Mercury. Note the rays of ejecta coming from some of the impact craters in the image. The Mariner 10 spacecraft was launched in 1974. The spacecraft took images of Venus in February 1974 on the way to three encounters with Mercury in March and September 1974 and March 1975. The spacecraft took more than 7,000 images of Mercury, Venus, the Earth, and the Moon during its mission. The Mariner 10 mission was managed by the Jet Propulsion Laboratory for NASA's Office of Space Science in Washington, D.C. (Image Note: Davies, M. E., S. E. Dwornik, D. E. Gault, and R. G. Strom, Atlas of Mercury, NASA SP-423, 1978; courtesy of NASA)

storms, ice, plate tectonics, or life. The surface of Mercury is less densely cratered than the Moon's, however, and some planetary geologists suggest that the oldest craters may be filled in by volcanic deposits. Some surface scarps, estimated to be more than 4 billion years old, are thought to represent contraction of the surface associated with the core formation and shrinking of the planet in the first half-billion years of its history.

The density of Mercury and the presence of a weak magnetic field suggest that the planet has a differentiated iron-rich core with a radius of approximately 1,118 miles (1,800 km), but it is not known whether this is solid or liquid. A mantle probably exists between the crust and core, extending to 311 to 373 miles (500-600 km) depth. The small size of Mercury means it did not have enough internal energy to sustain plate tectonics or volcanism for long in its history, so the planet has been essentially dead for the past 4 billion years.

See also Earth; Jupiter; Mars; Neptune; Saturn; solar system; Uranus; Venus.

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How To Survive The End Of The World

How To Survive The End Of The World

Preparing for Armageddon, Natural Disasters, Nuclear Strikes, the Zombie Apocalypse, and Every Other Threat to Human Life on Earth. Most of us have thought about how we would handle various types of scenarios that could signal the end of the world. There are plenty of movies on the subject, psychological papers, and even survivalists that are part of reality TV shows. Perhaps you have had dreams about being one of the few left and what you would do in order to survive.

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