LYCOS RETRIEVER 
Mercury (Planet): Spacecraft
built 655 days ago
The first up-close study of Mercury came with NASA’s Mariner 10 spacecraft, which passed Mercury twice in 1974 and once in 1975. It sent back pictures of a moonlike, crater-pocked surface. The spacecraft ... detected a magnetic field and provided data about the planet’s density and some of its surface chemistry. However, Mariner 10 could not orbit the planet and was only able to photograph about 45 percent of its surface, often in sunlight conditions that did not bring out features in maximum detail.
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Mercury is the closest planet to the Sun. This is the second-smallest planet within Earth's solar system. Upon the celestial sphere, Mercury ranges from -0.4 to 5.5, in apparent magnitude; Mercury is sufficiently "close" to the Sun that telescopes rarely examine it. Mercury has no natural satellites. The only spacecraft to approach Mercury was Mariner 10 (1974-75); only 40-45% of the planet has been mapped. The astronomical symbol for Mercury is a circle on top of a short vertical line with a cross below and a semicircle above the circle.
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Mercury is the closest planet to the Sun. It is smaller than the moons Ganymede and Titan but larger than the planet Pluto. It is heavily cratered, showing impact scars from countless bombardments by meteoroids. Old lava flows and quake faults ... mark its crust. Mercury has no atmosphere, but surprisingly, scientists have found evidence for a polar ice cap on this hot little globe. Mercury was explored in three flybys by the Mariner 10 spacecraft in 1974 and 1975.
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MESSENGER's Wide Angle Camera (WAC), part of the Mercury Dual Imaging System (MDIS), is equipped with 11 narrow-band color filters. As the spacecraft receded from Mercury after making its closest approach on January 14, 2008, the WAC recorded a 3x3 mosaic covering part of the planet not previously seen by spacecraft. The color image shown here was generated by combining the mosaics taken through the WAC filters that transmit light at wavelengths of 1000 nanometers (infrared), 700 nanometers (far red), and 430 nanometers (violet). These three images were placed in the red, green, and blue channels, respectively, to create the visualization presented here. The human eye is sensitive only across the wavelength range from about 400 to 700 nanometers. Creating a false-color image in this way accentuates color differences on Mercury's surface that cannot be seen in black-and-white (single-color) images.
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The only spacecraft to approach Mercury so far has been NASA's Mariner 10 (1974–75). The spacecraft used the gravity of Venus to adjust its orbital velocity so that it could approach Mercury—the first spacecraft to use this gravitational "slingshot" effect. Mariner 10 provided the first close-up images of Mercury's surface, which immediately showed its heavily cratered nature, and ... revealed many other types of geological features, such as the giant scarps which were later ascribed to the effect of the planet shrinking slightly early in its geological history. Unfortunately, the same face of the planet was lit at each of Mariner 10's close approaches, resulting in less than 45% of the planet's surface being mapped.
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As MESSENGER sped by Mercury on January 14, 2008, the Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS) captured this shot looking toward Mercury's north pole. The surface shown in this image is from the side of Mercury not previously seen by spacecraft. The top right of this image shows the limb of the planet, which transitions into the terminator (the line between the sunlit, day side and the dark, night side) on the top left of the image. Near the terminator, the Sun illuminates surface features at a low angle, casting long shadows and causing height differences of the surface to appear more prominent in this region.
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