Mercury (Planet) - Basic Properties, Mercury's Rotation Rate, Surface Features, Polar Ice, Internal Structure
solar system
Mercury is the closest planet to the Sun. It is a small world only slightly larger than Earth's Moon. Next to the planet Pluto, Mercury is one of the least explored planets within our solar system. Visited only once in all the years of solar system exploration (three brief fly-bys of Mariner 10 during 1974–75), only about 45% of Mercury's surface has been imaged from nearby. All that may change rather soon when NASA's Messenger and the European Space Agency's Beppi Columbo missions launch in 2004 and 2009, respectively.
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Mercury orbits the Sun at a mean distance of 0.387 astronomical units (AU). The high eccentricity of the planet's orbit (e = 0.206), however, dictates that it can be as far as 0.467 AU away from the Sun, and as close as 0.307 AU. The high eccentricity attributed to Mercury's orbit is the second largest in the solar system, only the planet Pluto has a more eccentric orbit. (Eccentrici…
When, in the mid-1880s, the Italian astronomer Giovanni Schiaparelli (1835-1910) attempted to construct a map of Mercurian features, he found that the shape and
Figure 2. A comparison of the internal structures of Mercury and Earth. Illustration by Hans & Cassidy. Courtesy of Gale Group.
relative position of the fuzzy surface features that his telescope could reveal did not change gr…
Mercury is a small planet that is quite hot (approximately 800°F [427°C] during a Mercurian day) when the Sun shines on its surface. It has a very thin atmosphere of oxygen, potassium, and sodium vapors. The surface pressure of atmosphere is too low to have wind. Without wind, running water, and flowing ice, the range of surface processes is limited to physical weathering effects of …
Perhaps one of the most unexpected Mercurian features to be discovered in recent times was that of water—ice at the planet's poles. The discovery of water ice on Mercury was made in 1991 by bouncing powerful radar signals off the planet's surface. The discovery of water ice on Mercury was surprising, since it was believed that the high daytime temperatures caused by the proxim…
Mercury's relatively large nickel-iron core and thin crustal mantle suggests that the planet may have undergone a catastrophic collision during its final stages of formation. A glancing blow from a large planetesimal may have caused most of the planet's initial mantle to be ejected into space, leaving behind a planet with a relatively large core. Instruments carried on-board Mariner …
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 atmos…
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